#chromosome segregation

[donnakori]

hey since you're in med school do you want to help me learn about obligate intercellular pathogens /j (don't take this seriously I'm just suffering)

Suffering w u babe im one nighting my review paper abt mitochondrial dysfunction causing dna fragmentation in geriatric oocytes leading to chromosomal nondisjunction

[mindblowingscience]

Among the many marvels of life is the cell's ability to divide and thus enable organisms to grow and renew themselves. For this, the cell must duplicate its DNA—its genome—and segregate it equally into two new daughter cells. To prepare the 46 chromosomes of a human cell for transport to the daughter cells during cell division, each chromosome forms a compact X-shaped structure with two rod-like copies. How the cell achieves this feat remains largely unknown. Now, for the first time, EMBL scientists have directly observed this process in high resolution under the microscope using a new chromatin tracing method. The research is published in the journal Cell.

Continue Reading.

[sumplysilly]

I love trans/nb/intersex ppl & I hope we can fucking grow up & move past wanting to segregate the genders. It literally helps no one. Degender clothes & presentation & voice pitch & body parts & chromosomes & hormones. Love all your genderfucked siblings. Reject the bio/gender essentialism that kiIIs us & don't let ppl that preach divine femininity say that they're transfemme & nb friendly now. This system doesn't work, don't let fuckheads try to sell it to you coated in blue pink & white glitter. I'm so fucking tired

[amber-tortoiseshell]

is antpelt's single black ear a realistic somatic mutation?

I have no idea how realistic it is, but i can imagine it happening.

Brown with a black ear... you know how i'd do this? I'd make him a tabby carrying solid (usually make canonically brown cat black tabbies anyway), then make a somatic mutation that results in losing the chromosome part that has the tabby allele. If everything is well and no genes are lost for which it's vitally important to have two copies (no idea how plausible that is), you can have a small solid black patch.

I had a class about a related topic a few weeks ago, so it's still vivid 😸 University is so useful! I can use what i learn to make warriors headcanons

Mosaicism as the result of incorrect chromosome segregation.

[five-thousand-loaves-of-bread]

…something been in draft for while:

idk how say this exactly but often like. use what look like binary clear cut dichotomy that have set definition this is this that is that. because oftentimes call “cake” “cake” instead of “flour milk egg baking powder salt etc etc” that kind language faster simplier and nuance can easily put word count 10k+. and. with language communication disabilities not always able translate all nuance into tangible word on paper/screen/type sometimes have to call something with imperfect blanket word. and then you find out other people not really hold as much nuance as you & still simplify your nuance into something binary this this that that

but reality rarely that binary— say on here that nonverbal mean not mouth speak at all all time & semiverbal is struggle all time but can mouth speak some & verbal but actually more nuanced than that like some severely apraxic people who mouth do say thing but not in their control not what they want say & they still call self nonspeaking because it not intentional meaningful speech; or someone labeled nonverbal who actually do commmunicate with mouth words just not full sentence & not full clear pronounce but still labeled nonverbal anyway as almost like microaggression of not recognize their single or two word mouth word phrase as valid enough communication worth listen to; or someone with echolalia that not mean anything with it (vs someone with echolalia that is use echolalia as communication (think gestalts, etc)); or some research showing even able say 1-2 words more ability than those with 0 word; or research debate about where minimally verbal end is it 20 words 30 words 50 words

when combat “go nonverbal” crowd often say there is clear cut about what nonverbal and what isn’t and yeah there is clear cut but also is there

many not ready for this level muddiness & nuance because some take bring nuance as invite to say like “i nonverbal but can still (intentionally) mouth speak” or gateway to claim nonverbality as if fun new identity collect instead of some complicated complex experience with mixed emotion but often some level of grief at some point that get lot targeted awful ableism & discrimination like denied education refuse accommodation like IEP or put in segregated classroom without even consider accommodation in general ed to isolate away from peers n not actual to help nonverbal person where they best thrive, or secluded or restrained, or denied healthcare, denied communication, which all still happen now btw it still common now it not rare obsolete it majority still

which make me feel like this image

[id: meme. left side is philosophers (school of athens painting) with caption “talking about nonverbal nonspeaking with other nonverbal people”. middle say “vs”. right side image is parent guiding infant to look play at toy and captioned “talking about nonverbal nonspeaking with not nonverbal people. end id]

because sometimes really is that but also even this is binary. thinking about how some motor nonspeaking people without intellectual disability who language okay say their mind intact that they not stupid thus deserve education and not deserve abuse and throw people with ID & language impairment. or how nonverbal nonspeaking from autism so different from (but so similar to) from motor apraxia from cerebral palsy from intellectual disability from genetic or chromosomal disorders from stroke from TBI from aphasia from vocal cord dysfunction from dementia from from from… how talking to someone nonspeaking from primarily motor reasons without cognitive intellectual language disabilities as someone nonverbal because high level autism cognitive language disabilities, we not guarantee understand eachother experience, same with talk someone from acquired things vs mine neurodevelopmental, how what i say about nonverbal here may not apply to someone who not speak not because autism etc

but “if words so meaningless if experiences so boundless let abolish all” not helpful because for all kind way be nonverbal there experiences that 100% not nonverbal there experiences so different from nonverbal “not able meaningfully intentionally speak all the time” for every meaningless there meaningful reason nonverbal people use nonverbal and deserve word “nonverbal” for ourselves and how this difference in experience is intracommunity issue issue within nonverbal nonspeaking community something we have to grapple with and not invitation for people outside to talk about how “if nonverbal so wide, drawing line at going nonverbal & say that isn’t nonverbal is ridiculous and gatekeep” because as much vast different experience there is reason why there community why there this word we all call ourselves and. not one. of the reason is we can slide in and out of not speak and speak daily or weekly or monthly or regularly. there still common theme to what we call nonverbal despite different

wide word isn’t “functionally useless” it just you not know how n when use it

& this conversation not just apply to nonverbal but many other words n other things as well

[kerryweaverlesbian]

My email to my MP about the UK supreme court 'women' ruling

(if you want inspiration for one of your own. I used the Trans Legal Project's template, which was very helpful. I might not get a response, but the emails for/against certain issues are tracked so might add up. Yours does not need to be this long, I just had a lot that I wanted to say):

Dear [MP's name], I hope you are well. I am a constituent of yours, and I have great concerns over the recent Supreme Court interpretation of the meaning of "woman" in the Equality Act, and the reactions of the present government as to what this means (as reported here in the Guardian). I have very close friends in the transgender community, and their right to exist in society is being infringed upon. 

The trans women I know, and I know them well, only want to exist as themselves. My [redacted personal story about how this ruling will specifically hurt someone I care about. I'm not telling it to the internet.].

What crime has she committed to be humiliated in this way?  For our government to try to edge her out of the society we live in, and pay for? She doesn't like to talk to strangers, let alone assault them in a bathroom or changing room or while accessing services. The material harm directly to her will be significant if this decision affects further policy decisions, to appease a fringe hate group. 

Transgender women are already at high risk of being assaulted, and now may be forced to use toilets that do not align with how they present themselves?! This is actively dangerous, it is leaving people I care about in the position to out themselves as transgender by walking into the men's room in a dress or a skirt (just how safe does that sound to you?), break the law, or risk serious ill-health by not using the toilets when required. A lot of the trans friends I have disabilities that would make this risk untenable. 

How, exactly will this be upheld? Is anyone presenting as a woman going into a changing room going to be policed for her upholding of traditional gender stereotypes? Will someone from the staff of a building be inspecting people's genitals...? I certainly don't feel comfortable with anyone being subjected to that! Either the women being humiliated and sexually harassed by it happening, or the person now forced to look at people's genitals all day. That's not the kind of world I want to live in.  Or perhaps it will be a card to show the results of a forced chromosome test (where's that money coming from?) - despite the fact that many cis women might have an xxy chromosome and not know it. I'm a pretty forgetful person - I forget my Gender Card and I can't go to the toilet? It's a ridiculous idea. Gender non conforming cis women will undoubtedly also be targeted and policed in an effort to remove trans women from women's spaces. Cis women with features perceived as masculine - large hands, deep voices, mustaches, prominent hairiness - all perfectly normal things to be on a woman - will be targeted too. A women being barred from using the women's toilets can lead to UTIs, toxic shock from leaving tampons in and other serious health conditions. 

It is already a crime to assault someone in the bathroom, and the gender marker on the door does not stop the people who do that. Trans women would be targeted, potentially by law, on the basis of their identity. Where is the equality in this? Made guilty until proven guilty. Trans women have been using women's toilets since at least the 1970s, as per a statement read in Parliament on the 22nd, and yet women have broadly felt safe to use the bathroom this whole time. This rhetoric of fear is one that has been levied against all marginalised groups to try and eradicate them from society. Black segregation in America, "fears" about gay men.  

And barring trans women from women's sports - literally where else are they supposed to go? After sufficient time on estrogen, she no longer has any of the (supposed) gendered advantages (in sports such as fencing and skateboarding as was recently in the news on this topic....there isn't one...) so, what, she's supposed to be stuck underperforming and harassed on men's teams? And for transgender children too - why discourage children of any gender from playing sports with the team that makes them feel happiest to play in? Why empower children and teenagers with discrimination on a legal level to continue to bully and harm their peers, which can and has escalated to murder and manslaughter? Trans women have been in women's sports globally for years now  - the (frankly, sexist) fears of some that they will obviously dominate "the weaker sex" has NOT come to pass. Cis and trans women deserve a better consideration and respect from the government that claims to represent us. 

Aren't there more pressing women's matters for government than stopping women from playing sports and using the toilets? The gender pay gap spurred by zero hour contracts, for example, or creating regulations to ensure that medical tests are performed on cis female test subjects, cells and animals to ensure they work as intended on women throughout the menstrual cycle. The violence against women disproportionately conducted by cis men. 

It is shocking to me that the Supreme Court heard out multiple anti-trans groups, but did not hear from a single trans activism group, on a matter that very obviously predominantly targets trans women. It has made me afraid that the Equality and Human Rights Commission will do the same when it comes to the Equality Act Statutory Guidance. Whose voices count the most? Those who have enough money to fund a campaign to stigmatize an already marginalised group? 

I hope you will fiercely advocate for the wants of your constituency on debates and votes around this issue. I would very much like to meet to talk about this further, I feel extremely strongly on this issue. I can be reached through this address.

Sincerely,

[My name and home address, to prove I'm in this MP's catchment, important!!]

[coochiequeens]

Someone should ask Colleen Martin and other members of the Lucia Mar Unified School District (LMUSD) board if they would have like changing in front of members of the opposite sex while they were students

By Jackson Thompson April 18, 2025

A school board meeting in California featured emotional debate over transgender athletes being allowed to share locker rooms with high-school girls. One girl who cried during a speech was told to "wrap it up" by the board president. 

During the Lucia Mar Unified School District (LMUSD) board meeting on Wednesday, a high-school junior girls' track athlete at Arroyo Grande High School named Celeste Diest took the podium to recount her experience of having to change in front of a biologically male trans athlete before practice, while that athlete allegedly watched her undress. 

"I went into the women's locker room to change for track practice where I saw, at the end of my row, a biological male watching not only myself, but the other young women undress. This experience was beyond traumatizing," Diest said, as she began to choke up and cry. 

Diest then fought through her tears to argue that the trans athlete's XY chromosomes define the person as a male, adding, "That is basic biology."

But Diest was then interrupted by LMUSD board president Colleen Martin. 

"Okay, please wrap it up," Martin said, gesturing to Diest to finish her point. 

The teen then sniffled and continued speaking. 

"I just want to ask ‘what about us?’ We can not sit around and allow our rights to be given up to cater to an individual that is a man, who watches women undress and is stripping away female opportunity that once was fought for us. Sadly we have to try and regain our rights back. I hope you put effort into the restoration of our school safety." 

Diest then walked away from the podium to a roaring applause from the audience before Martin tried to silence the cheers. 

"No!" Martin yelled when the cheers got louder. 

Then, Martin just sat there silently as the applause continued for several more seconds, before it finally tempered, and the next speaker gave another speech opposing trans inclusion. 

Prior to Diest's speech, one of the other speakers, a woman named Shannon Kessler, who was scheduled to go after the teen, asked Martin whether she could give her speaking time to Diest. But Martin denied that request. 

"We're not doing that," Martin said. 

Several other parents gave speeches in opposition of trans athletes in attendance, while other community members spoke in support of trans inclusion. 

California has been one of the many blue states in the nation to defy President Donald Trump's "Keeping Men Out of Women's Sports" executive order, and has allowed trans athletes to compete with girls for over a decade. 

A law called AB 1266 has been in effect since 2014, and gives California students at scholastic and collegiate levels the right to "participate in sex-segregated school programs and activities, including athletic teams and competitions, and use facilities consistent with his or her gender identity, irrespective of the gender listed on the pupil’s records."

California Code of Regulations section 4910(k) defines gender as: "A person’s actual sex or perceived sex and includes a person’s perceived identity, appearance or behavior, whether or not that identity, appearance, or behavior is different from that traditionally associated with a person’s sex at birth." CIF Bylaw 300.D. mirrors the Education Code, stating, "All students should have the opportunity to participate in CIF activities in a manner that is consistent with their gender identity, irrespective of the gender listed on a student’s records."

These laws and the subsequent enabling of trans athletes to compete with girls and women in the state has resulted in multiple controversies over the issue over the last year alone. 

The California Interscholastic Federation (CIF) said it will continue to follow the state's law that allows athletes to participate as whichever gender they identify as, a spokesperson told Fox News Digital. 

"The CIF provides students with the opportunity to belong, connect, and compete in education-based experiences in compliance with California law [Education Code section 221.5. (f)] which permits students to participate in school programs and activities, including athletic teams and competitions, consistent with the student’s gender identity, irrespective of the gender listed on the student’s records," a CIF statement said. 

The California state legislature's Democrat majority rejected two bills that would have changed state law to ban trans athletes from girls' sports on April 1. 

[omegaversetheory]

Assuming that the A/B/O labels are based in genetics, I Wonder if you have any headcannons for genetic disorders?

In my AU, I like to imagine that some people usually believe that persons who have an "extra alpha chromosome" or an "extra omega chromosome" are blessed because they would be like "super alphas" or "super omegas" due their increased capacities when it comes to strenght, size, fertilitie...when in reality they are only partially true.

Sure, those "super alphas and omegas" are more "powerful" when it comes to these característics, but overall, they arent sacred individuals nor super heroes or nothing like that, they are chronically ill people that usually present a lot of health complications that in most cases overcomplicates their daily lives or even can shorten their lifespans (for example, said "super omegas" would be way smaller than the average omega, which usualy leads to frequent bone pains due the incorrect development and consequent malformation of their bones) I also imagine said "super alphas and omegas" being very prone to suffer mental illnesses since the massive amount of hormones they segregate would make them turn into very problematic individuals in general (for example making omegas to be extremely volatile and emotionally irrational individuals, or alphas to have a weird mix between a higly stoic nature and maximized protection instincts, causing them to either become toxic/ manipulative or directly psychopats)

Hi!

What an interesting idea. In my au, well I've never thought about it, but I'd also say that they would be ill, if not extremely chronically ill, people. Depending which age you're writing in, I'd venture to guess there just may not be many of these people around - they would've died very young without the proper medication and constant treatment. That also leads into a larger scientific question about how many chromosomes people in omegaverse have and how exactly their genetics operate. A conversation I'd need a much better grasp of biology and genetics to answer! So I leave it "behind the curtain" in my au, and in fact it's never come up. But if it does, I'll be sure to post.

My notion that having extra chromosomes may result in chronic illness is based on the idea that they probably have more chromosomal pairs or some other genetic system - one that would make the extra material very unlike the human world. Here we see trisomy - which leads to conditions like Down Syndrome. People with DS can now live very fulfilling and rich lives, but it wasn't always that way and it still isn't smooth sailing for many.

I don't use the "super powered" "ultra alpha/omega" headcanons in my au but let's see what we can whip up for you.

It gives the bearer a stronger scent and a better ability to interpret other people's scents.

Decreases fertility and ability to reproduce

Longer heats/ruts that are more intense emotionally/mentally and may cause pain like cramping, migraines, and nose bleeds.

May cause allergic reactions to foods, natural products, etc... This is a common sign (besides infertility) of the condition. Common allergies include - dairy, wheat, some meat products, and nightshades. Some bearers may also have allergic reactions to biological fluids and substances that are not their own including saliva and other natural lubricants.

Have a slightly higher endurance.

[bpod-bpod]

Cracking an Egg

Cell division involves chromosomes being segregated on a protein spindle so each daughter cell receives them equally. In egg cells the spindle forms without chromosome involvement – this study in the C. elegans worm reveals the vital role of an enzyme called ZYG-8 in stabilising such spindles

Read the published research article here

Image by Emily Czajkowski and Sadie Wignall, from work by Emily R. Czajkowski and colleagues

Department of Molecular Biosciences, Northwestern University, Evanston, IL, USA

Image originally published with a Creative Commons Attribution 4.0 International (CC BY 4.0)

Published in and on the cover of PLOS Genetics, September 2024

You can also follow BPoD on Instagram, Twitter and Facebook

[tunnaa-unnaa]

im kind of uniformed about trans issues but saw your reblog about valentine. im genuinely not trying to argue i just want to understand, isnt sex segregation in sports in order to achieve fairness and give female people a chance to succeed? why should valentine be allowed? if im understanding correctly she is amab? sorry if im wording this question incorrectly, im genuinely just not informed and am only finding extremely opinionated people who mis-pronoun when i google her, genuinely just want to understand why people are in favor of her racing with female people

First of all, thanks for reaching out and being curious! I'm probably not the best at answering this since it's not my post and I'm just a random reblogger, but I'll try my best to give some links to better sources.

Sex segregation isn't actually necessary in sports. You might be familiar with how in wrestling or other combat sports, participants are divided into classes depending on body weight. More body mass, more muscle. Wouldn't be fair putting a 80kg guy against a 130kg guy, makes sense. Which brings us to the question: Why aren't sports segregated by categories like that - categories that provably, measurably make a difference in the sport at hand? Why do we segregate them by sex, somehow implying that a 130kg woman wrestler would be at a disadvantage against that 80kg man from earlier? Or a 130kg man for that matter?

Here is an article going deeper into this topic: The Problem with Sex Segregated Sport Here's another: Separating Sports by Sex Doesn’t Make Sense

It's easy to think women are inherently weaker than men, because that's what we keep getting told over and over, but both chromosomal sex and the biology around it are far more complex than that. It's a lot more nurture than nature the more research gets done.

Which brings us to trans people. If neither sex is inherently stronger, why gatekeep trans athletes from competing against people of the same gender?

Here's a systematic review examining how the restrictions placed on trans people in sports lack evidence to back them up, as we do not have any proof that being trans gives any kind of advantage: Sport and Transgender People: A Systematic Review of the Literature Relating to Sport Participation and Competitive Sport Policies

Another issue with gatekeeping trans people from sports is that it adds onto and reinforces other cultural biases and exclusion of transgender people. It's more important to let people with all kinds of bodies participate, than to exclude some entirely in the name of fairness. Sports are all about measuring biological advantages between individuals. So it highlights a very specific kind of bigotry when the imagined advantage trans people supposedly have is seen as a problem even when there's no evidence of such.

Here's another post I've reblogged that points out how this obsession with biological essentialism - thinking that women inherently perform differently in sports than men - is also hurting intersex people. People whose bodies do not fall into either binary category should also be allowed to compete without intrusive examinations. We should categorize sports based on performance and ability, not sex.

That's the basic gist of things. Thanks again for being interested in the topic! Others are free to add to this post or correct me.

(terfs DNI)

[i-should-have-studied]

Zoology Sem 4 End - Mod 3

Law of Segregation

Mendel’s Law of Segregation explains how the alleles responsible for a specific trait separate during the formation of gametes and how they are passed onto the offspring.

Each individual possesses two alleles for a particular trait, one inherited from each parent. During gamete formation, the alleles separate from each other, so that each gamete carries only one allele for each trait.

Since each gamete carries only one allele for a trait, they are considered pure for that particular characteristic.

This law is significant as it introduced the concept of hereditary factors that remain as separate entities even when present together with other similar entities.

The law was used to disprove the blending traits theory encoded by recessive alleles in the F1 generation.

This law enables the use of Punnett squares for the estimation of resulting genotypes from a cross as it is based on the equal segregation of alleles.

- pic

This law is based on the first phase of the meiosis, where the homologous chromosomes with two copies of the same gene are segregated into individual daughter nuclei.

The division of homologous chromosomes during meiosis can account for the segregation of the alleles at the gene locus to form different gametes.

-

Example of Mendel's Law of Segregation

Monohybrid cross between tall and drawf pea plants.

Assume the tall homozygous pea plant parent has the alleles TT and the short plant parent has tt genotype.

The parent with TT genotype produces gametes with a single T allele while the parent with tt genotype produces singular t gametes.

As a gamete can only have a single chromosome of a homologous pair, each gamete carries one allele.

During the cross, the gametes fuse together to form a heterozygous plant with Tt genotype with both dominant and recessive alleles.

As a result of dominance, the dom T allele expresses itself in the hybrid of the first gen while the rec t allele remains unexpressed.

In heterozygous individuals, both the alleles remain together but do not interfere or affect each other.

diagram ig

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Inborn Errors of Metablolism

Inborn errors of metabolism are genetic diseases which effect the metabolic pathways.

Also called inherited metabolic disorders.

They involve the failure of break-down or storage of carbohydrates, fatty acids, and proteins due to an enzyme defect.

These diseases are rare, occur in 1/2500 births.

The cause of the majority of these are due to defects in single genes which code for enzymes that facilitate conversion of various substrates into products.

Due to decreased enzyme activity, these disorders cause specific compounds to accumulate in the body to toxic levels.

These metabolic disturbances, if untreated, may result in cognitive impairment, organ failure and ultimately death.

They can being to present at any age.

Awareness of these diseases, their presentations, and their evaluation is critical for their management.

Many IEM’s are screened for at birth via the Heel Prick Test, newborn screening allows early identification and initiation of treatment, improving patient outcomes

-

One Gene-One Enzyme Hypothesis:

Originally hypothesized by Beadle and Tatum

Principle: - All biochemical processes in all organisms are under genetic control. -The overall biochemical process are resolved into a series of individual step-wise reactions. - Each single reaction is controlled by a single gene. In every case a 1:1 correspondence of gene and biochemical reaction exists - Mutation of a single gene results only in an alternation in the ability of the cell to carry out a single primary chemical reaction. - The underlying hypothesis is that each gene controls the reproduction, function, and specificity of a particular enzyme:

ex: Albinism

It is a rare autosomal recessive genetic condition caused due to mutation in the tyrosinase gene (TYR)

TYR is on chromosome 11q14 There is a complete lack of tyrosine activity characterized by hypopigmentation at birth

Melanin controls skin, eyes, and hair pigmentation.

People with albinism have extremely pale skin, hair and also affects the vision.

The TYR gene product, tyrosinase, normally hydroxylates tyrosine to DOPA and oxidizes DOPA to melanin. Loss of this function leads to an inability to synthesize melanin.

People with albinism should avoid prolonged UV light exposure.

Corneal lenses should have UV protection. Bifocals and low vision aids may be considered in older children and adults.

---

Monohybrid and Dihybrid Cross

Monohybrid Cross

A monohybrid cross is a type of genetic cross between two individuals who differ in only one trait.

It is the study of inheritance patterns for a singular trait, with a focus on a single gene with two opposing alleles.

Two heterozygous individuals for a specific trait are crossed. One allele is inherited from each parent, the progeny are observed to determine the inheritance and expression of that specific trait.

In monohybrid crosses, the dominant allele is expressed in the phenotype while the recessive allele is only expressed in the absence of the dominant allele. This allows us to identify which allele is dom over the other.

Monohybrid crosses follow the principles of Mendelian inheritance, established by Gregor Mendel.

Monohybrid crosses are often illustrated using a Punnett square, an illustration which helps to predict the ratio of phenotypes and genotypes in offspring.

-

Ex of Monohybrid Cross: Mendel's Peas Experiment

George Mendel used the monohybrid cross to determine the dominant and recessive traits in the case of peas.

An example of one of the experiments is the height of the plant. Some plants were taller while the others are shorter.

The homozygous genotype for the tall pea plant is TT, and the homozygous genotype for the dwarf pea plant is tt.

A monohybrid cross between the two plants resulted in the production of heterozygous genotype Tt in the F1 generation.

The phenotype of the F1 generation plants was tall, indicating that the tall allele is dominant over the short allele.

Then, the F1 gen plants were self crossed to produce F2 generation where a consistent ratio of tall:dwarf plants was observed.

Around 75% of the plants displayed the tall phenotype, while the remaining 25% exhibited the short phenotype.

Phenotypic Ratio: 3:1

Genotypic Ratio: 1:2:1

cross

-

Dihybrid Cross

A dihybrid cross is a type of genetic cross between two individuals who differ in two traits simultaneously.

More complex than monohybrid crosses, involves two genetic traits where the parents can be either homozygous or heterozygous.

The number of gametes and offspring formed during a dihybrid cross is more than those during a monohybrid cross. These have more phenotypic variation than the ones obtained from monohybrid crosses.

Dihybrid crosses follow the principles of Mendelian inheritance, established by Gregor Mendel, specifically it is a good example of the law of independent assortment.

But it only works in the case of genes that are not linked and are present on different chromosomes.

Dihybrid crosses are often illustrated with a Punnett square with four rows and four columns. It helps to predict the genotypes and phenotypes of the offspring

draw

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Ex of Dihybrid Cross: Mandel's Pea Experiments again

Cross between homozygous pea plant with round yellow seeds and homo plant with wrinkled green seeds.

The round yellow seeds are represented by RRYY genotype, the wrinkled green seeds are represented by rryy.

The gametes formed from these alleles are RY and ry respectively.

On crossing, F1 forms with yellow round seeds and RrYy genotype.

The four alleles can combine into four different combinations: RY, Ry, rY, and ry.

The four alleles are assorted randomly to produce four types of gametes.

The gametes unit at random during fertilization to produce sixteen types of individuals in the F2 generation, the ratio being 9 round yellow, 3 round green, 3 wrinkled yellow, and 1 wrinkled green.

Phenotypic Ratio: 9:3:3:1

Genotypic Ratio: 1:2:1:2:4:2:1:2:1

cross

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Linkage and Crossing Over

Linkage is the phenomenon of genes staying together throughout inheritance through several generations without any change or separation due to their presence on same chromosomes.

It refers to genes that are located on the same chromosome.

Linked genes do not show independent assortment.

Unlinked genes show independent assortment

Linkage involves at least 2 genes which are found on the same chromosomes in a linear fashion.

It reduces variability.

It usually involves those genes which are located close to each other.

The strength of linkage depends on the distance between the linked gene, lesser the distance greater the strength of linkage.

The types of linkage can be classified on the bases of: - Crossing over - Chromosome involved - Gene involved.

On the Basis of Crossing Over:

Complete Linkage - If at least two traits are inherited together and consistently appear in two or more generations in their original or parental combinations - These genes do not produce non-parental combinations. Genes showing complete linkage are closely located on the same chromosome. - It is rare but has been reported in Drosophila male.

Incomplete Linkage - Exhibited by those genes which produce some percentage of non-parental combinations. - Such genes are located distantly on the chromosome. - It is due to accidental or occasional breakage of chromosomal segments during crossing over. - Incomplete linkage has been observed in peas.

On the Basis of Chromosomes Involved:

Autosomal linkage - Linkage of genes on autosomes

Allosomal linkage - Linkage of genes on sex chromosomes

On the Basis of Genes Involved:

Depending on whether all dominant or some dominant and recessive alleles are linked together

Coupling Phase - when genes come from the same parent, they enter the same gamete and inherited together. - Dominant alleles and recessive alleles present on the same chromosomes shows coupling phase

Repulsion Phase - when genes are inherited separately they come from different parents and enter different gametes. - Dominant alleles of same genes are linked with recessive alleles of other genes on same chromosomes shows repulsion phase

-

Crossing over is the exchange of genetic material, leading to genetic recombination

It occurs between non-sister chromatids. One chromatid from each of the two homologues chromosomes is involved in crossing over.

Leads to re-combinations or new combinations between linked genes.

Crossing over of two genes generally yields two recombinant types or crossover types and two parental types or non-crossover types.

Generally leads to exchange of equal segments or genes and recombination is always reciprocal.

It begins at pachytene stage of prophase-I of meiosis

There are 2 ways to classify crossing over: - Based on Cell Type - Based on Number of Chiasmata

Based on Cell Type:

Somatic or Mitotic Crossing over - Occurs in the chromosomes of somatic cells during mitosis. - Relatively rare, does not have significant genetic implications.

Germinal or Meiotic Crossing over - occurs in germinal cells during meiosis, specifically during the formation of gametes - Universal, plays a crucial role in genetic diversity. - Involves the exchange of genetic material between homologous chromosomes - Essential for proper chromosome segregation and genetic variation.

Based on Number of Chiasmata:

These are all types of equal crossing over in germinal cells

Single Cross Over - Formation of a single chiasma - genetic material is exchanged between two chromatids out of the four present in a tetrad. - Relatively straightforward genetic recombination

Double Cross Over - Formation of two chiasmata - Can involve two, three, or all four chromatids. - Results in a more complex recombination of genetic material - Leads to a higher variability in the resultant chromatids

Multiple Cross Over - Formation of more than two chiasmata - Relatively rare, occurs less frequently than single and double cross overs. - Multiple cross overs can involve extensive genetic recombination.

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Mendel's Laws of Inheritance

There are 3 laws of inheritance: -Law of Dominance -Law of Segregation -Law of Independent Assortment

1) Law of Dominance

When there are 2 alternate forms or alleles of a particular trait present in an organism, one allele will be dominant and the other recessive.

In heterozygous genotypes, only the dominant allele is expressed, while the recessive allele remains masked away.

This law explains how the traits of the parents are expressed in the offspring during a monohybrid cross.

ex: When crossing a homozygous tall pea plant (TT) with a short pea plant (tt), a heterozygous tall pea plant is observed (Tt). Despite the presence of a t allele, only the tall trait is shown.

cross

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2) Law of Segregation

Also called the law of purity of gametes.

This law explains how the alleles responsible for a specific trait separates during the formation of gametes and how they are passed onto the offspring.

Each individual possess two alleles for a particular trait, one inherited from each parent. During gamete formation, the alleles separate from each other, so that each gamete carries only one allele for each trait.

Since each gamete carries only one allele for a trait, they are considered pure for that particular characteristic.

ex: During the same monohybrid cross between tall and dwarf pea plants, the gametes T and t are retained throughout the crosses

cross

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3) Law of Independent Assortment

Alleles for different traits separate and are inherited independently during the formation of gametes.

The alleles for one trait is not linked or influenced by the alleles for other traits.

ex: Mendel's dihybrid cross (round yellow + wrinkly green)

cross

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Chromosomal Mutations

Chromosomal mutation refers to change in the structure or number of chromosomes within a cell, impacting genetic information and potentially leading to various genetic disorders.

Chromosomal mutations often arise from mistakes during cell division, crossing over, mutagen exposure, and even simply inherited from previous generations.

They can be detected by microscopic examinations or genetic analysis.

Chromosomal mutations may be categorized as Chromosomal Mutations I and II.

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Chromosomal Mutations I:

Structural mutations which arise as a result of alterations in the structure of the chromosomes.

Structural mutations are further divided into 4 different types - Inversion - Deletion - Duplication - Translocation

Inversion: - occurs when a chromosome segment breaks off, rotates 180 degrees, and reattaches. - This reverses the order of the genes within that segment. - There is no net loss or gain of genes, simply a rearrangement of the sequence. - This structural rearrangement can disrupt gene function and may lead to genetic disorders or affect the chromosome’s ability to pair properly during meiosis. - ex: Inversion of chromosome 12 created the tallest teenager in the world at 7ft 9in.

Deletion - involves the loss of a chromosome segment due to breakage. - results in the absence of certain genes. - can lead to a deficiency in genetic material, which may cause developmental abnormalities or genetic diseases if crucial genes are missing. - chromosomes that have undergone deletion cannot revert back to normal and, if transmitted to the next generation, can be hereditary. - ex: Deletion of the short arm of chromosome 5 in humans results in ‘cri du chat’ syndrome where babies cry like cats.

Duplication/Amplification - occurs when a chromosome segment is copied and inserted into the genome - results in multiple copies of that segment - An increase in gene dosage can disrupt normal cellular function, may contribute to cancer or other genetic disorders - ex: duplication of a segment of the X-chromosome, called section 16A, in Drosophila. Codes for bar traits like narrower, oblong, bar-shaped eye with a few facets.

Translocation - involves the exchange of chromosome segments between nonhomologous chromosomes. - No net gain or loss of chromosomes or genes during translocation but a rearrangement - The rearrangement can create novel gene combinations and may result in genetic disorders or increased susceptibility to cancer due to disrupted gene function.

The exchange of chromosome sections generates new linkages with possible new phenotypes.

ex: translocation of chromosome 21 onto the 14th chromosome causes down syndrome.

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Chromosomal Mutations II:

Includes mutations that are caused by alterations in the number of chromosomes in a cell.

Change in the no of whole chromosomes is called heteroploidy.

It produces phenotypic changes, modifications of phenotypic ratios, and alteration of linkage groups.

Heteroploidy can be further classified into: - Aneuploidy - Polyploidy

Aneuploidy - characterized by an abnormal number of chromosomes in a cell, either through an excess or deficit of chromosomes. - Aneuploidy resulting from the loss of chromosomes is called hypoploidy - Resulting from the addition of chromosomes is called hyperploidy. - Hypoploidy occurs due to the loss of a single chromosome (monosomy) or a pair of chromosomes (nullisomy). - Hyperploidy, might involve the addition of a single chromosome (trisomy) or the addition of a pair of chromosomes (tetrasomy). - Aneuploids are caused by a result of nondisjunction during mitosis or meiosis. - Aneuploidy in animals causes some genetic imbalance leading to higher mortality or reduced fertility. - ex: Down's syndrome, trisomic condition of chromosome no 21.

Polyploidy - The presence of more than two complete sets of chromosomes in a cell. - Polyploidy includes different combinations like triploid (3n), tetraploid (4n), pentaploid (5n), hexaploid (6n), and octoploid (8n).  - Polyploidy higher than tetraploid is not common in natural environments, but can be observed in some plants - Polyploidy can be further divided into autopolyploids and allopolyploids. - Autopolyploids have the same basic set of chromosomes but multiplied to form multiple sets. - Allopolyploids result from the doubling of chromosome number in a hybrid from two different species. - ex: Doob grass, triploid and sterile, propagates vegetatively.

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5M: Sex-Linked Inheritance

The inheritance of a trait that is determined by a gene located on one of the sex chromosomes.

The genes which occur exclusively on the X chromosome are called X-linked genes.

The genes which exclusively occur in Y chromosome are called Y-linked or holandric genes.

Genes occurring only in the X chromosomes are represented twice in female, because females have XX genotyping and only once in male because of the XY genotyping.

In males, the differential region of each chromosome has genes with no counterparts on the other kind of sex chromosome. These genes, whether dominant or recessive, show their effects in the male phenotype. Such genes in the differential regions are called hemizygous in males.

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Inheritance of X-Linked Recessive Genes

In X-linked recessive inheritance, the genetic trait is linked to the X chromosome and recessive.

Since males have only one X chromosome inherited from their mother, any recessive gene present on it will be expressed, since there is no second X chromosome to mask the effect.

Since females have two X chromosomes, they must carry the affected allele on both their chromosomes in order to express the recessive trait.

Women can carry a defective gene without showing symptoms if the other X chromosome has a normal copy of the gene. This makes these women carriers of X-linked recessive traits.

Therefore, X-linked recessive disorders are more frequently observed in men than in women.

An example of an X-linked recessive disorder is red-green color blindness.

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Inheritance of X-Linked Dominant Genes

In X-linked dominant inheritance, the genetic trait is linked to the X chromosome and is dominant.

X-linked dominant disorders are less common compared to X-linked recessive disorders.

The presence of just one copy of the dominant gene on the X chromosome is enough to express the trait in both males and females.

However, the phenotypic expression is typically less severe in females compared to males due to the compensatory effects of the second X chromosome

Women can receive the trait from either papa or mother while men can only receive it from mommy

ex: Vitamin D-resistant rickets

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Inheritance of Y-Linked Genes

Also called Holandric Inheritance

Less common since the Y chromosome contains far fewer genes than the X chromosome.

Y-linked genes are passed directly from father to son and are responsible for male-specific traits

The most notable gene on the Y chromosome is the SRY gene, which plays a pivotal role in determining male sex by initiating the development of male reproductive organs.

ex: Excessive development of hair on ear

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Non-Mendelian Laws of Inheritance

[sproutystudies]

Polyploidy

Hello, hello! Since my study species, cultivated strawberry, is a polyploid organism, my first educational post is on polyploidy.

While most animals are diploid, meaning that they have two sets of chromosomes, it is common for plants to have additional sets of chromosomes. When an organism has more than two complete sets of chromosomes, this is known as polyploidy. This can be contrasted to aneuploidy, which is when an organism has a loss or gain in chromosomes that results in one or more set being incomplete.

There are two main types of polyploids. Autopolyploids arise from genome duplication within a single organism or species (Lloyd & Bomblies, 2016). This can either occur from spontaneous whole genome duplication due to endoreduplication (mitotic failure) or from self fertilization following meiotic error. During mitotic failure, the genome is doubled in preparation for cell division but the cell fails to divide (Shu et al, 2018). During meiotic error, chromosome sets fail to segregate, leading to formation of an unreduced gamete (Spoelhof et al, 2017). Autopolyploids have increased vigor due to larger nucleus size and greater protection from recessive deleterious mutations, but they do not gain different genetic information like in allopolyploids.

Allopolyploids arise from hybridization between two closely related species (Lloyd & Bomblies, 2016). There can be variation in the steps to allopolyploid formation. Notably, an allopolyploid arising from genome duplication of a sterile hybrid can be called an amphidiploid, and an allopolyploid arising from two polyploid parents can be called an amphipolyploid. Allopolyploids have increased vigor for the same reasons as autopolyploids but also have the advantage of new alleles being introduced. As alleles on some chromosomes are lost or silenced over time, favorable alleles can be conserved through natural or artificial selection. The various advantages conferred by allopolyploidy are together known as hybrid vigor.

Cultivated strawberry is an allo-octoploid, meaning it has eight sets of chromosomes with variation in their species of origin. These chromosomes diploidize to form four sub-genomes, known as sub-genome A-D. This means that most genes exist in quadruplicate. A gene in one sub-genome is known as a homeologue of its counterparts in other sub-genomes. The term homeologue is derived from the term homologue, which refers to genes with a shared origin.

Cultivated strawberry is also an amphipolyploid, as it arose from hybridization of two octoploid parents (Edger et al, 2019). Each of these parents originated from four diploid progenitors (Edger et al, 2019). These progenitors are believed to be F. iinumae, F. nipponica, F. vesca, and F. viridis (Edger et al, 2019). The genomes of each of these progenitors form the sub-genomes of the octoploids.

Figures in this post are from Hegarty & Hiscock, 2008. The strawb picture is my own.

Important Terms: polyploidy, aneuploidy, autopolyploid, allopolyploid, endoreduplication, unreduced gametes, alleles, homeologues, hybrid vigor

When the Winter quarter starts I plan to make these educational posts a weekly thing, largely to help prepare for my qualifying exam, but hopefully they will be useful to others as well. If there are topics related to my studies that are particularly interesting to anyone, feel free to reach out so I can prioritize them :)

[cynda-queer]

Meiosis is a specialized cell division process that occurs in sexually reproducing organisms to create gametes, or sex cells (sperm and egg).

Mitosis is the process by which a cell replicates its chromosomes and then segregates them, producing two identical nuclei in preparation for cell division.

You can tell I work with bacteria and dead things where binary fission is the method of reproduction.

I'm picturing the logistics of mitotic reproduction of Toothless. What is it? S, G1, G2, PMAT + Cytokinesis?

That's for your, Professor Buckley. I did learn things in your class.

[bpod-bpod]

In a Spindle

Live imaging and electron tomography in cells of the tiny worm Caenorhabditis elegans (C.elegans for short) reveal fine details of the changes in cell structure occurring during female meiosis – specialised cell division for sexual reproduction to produce egg cells with only one pair of chromosomes. The length of the meiotic spindle (a transient assembly of proteins that forms to segregate chromosomes) is correlated with the length of microtubules – tiny flexible pipes formed of a protein called tubulin – which comprise most of the spindle proteins.

Read the published article here

Image from work by Vitaly Zimyanin and Stefanie Redemann

Department of Molecular Physiology and Biological Physics, University of Virginia School of Medicine, Charlottesville, VA, USA

Image originally published with a Creative Commons Attribution – NonCommercial – NoDerivs (CC BY-NC-ND 4.0)

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[digikavi]

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