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Brady Yoon
2005-Feb-23, 04:36 AM
I have a question about meiosis.

Ok, let's say there is a female and her egg cells are dividing through
meiosis. Independent assortment occurs and the homologous chromosomes
are split and each half enters one of the two cells that form as a
result of the first division. Homologous chromosomes are made up of a
male component and a female component (I think), so let's say that all
of the female components of the homologous pair go into one of the
divided cells. Wouldn't it have to find a male sperm with exclusively
male components in order to be fertilized?

So my question is that do the female and male number of chromosomes in
haploid cells have to match between gametes in order for reproduction
to occur? For example, there's an egg with 23 chromosomes, and 18 of
them are female and 5 of them are male, and there's a sperm also with
23, with 16 of them male and 7 female. Am I right in saying that the
sperm couldn't fertilize the egg and the egg would need a sperm that
had 18 male and 5 female to complete the homolgous chromosomes in the
zygote so the male=female?

This is the only thing I'm not getting.. Help would be appreciated.

W.F. Tomba
2005-Feb-23, 04:50 AM
When you say male and female, are you talking about some kind of "hardware" configuration? I don't think chromosomes have a biological sex. One member of each homologous pair is inherited from a male and the other is inherited from a female, but I don't think that implies a fundamental difference in the chromosomes (except of course in the case of the X and Y chromosomes in species that have their sex determined that way).

Brady Yoon
2005-Feb-23, 04:59 AM
When you say male and female, are you talking about some kind of "hardware" configuration? I don't think chromosomes have a biological sex. One member of each homologous pair is inherited from a male and the other is inherited from a female, but I don't think that implies a fundamental difference in the chromosomes (except of course in the case of the X and Y chromosomes in species that have their sex determined that way).

Yeah, that's want I know is right, but my way of thinking is weird. I have to go through every single detail until everything logically makes sense. I get stuck sometimes, obviously. :)

What you're trying to say is that the chromosomes in each human that are labeled as the "female portion" and the "male portion" only came from a female or male, and that the actual chromosome is not fundamentally different? I think I'm getting it now.

Brady Yoon
2005-Feb-23, 05:05 AM
Ahh, I see! The independent assortment merely promotes genetic variability, and the male and female labels are only there to say which parent it got it from.

Thanks, W.F. Tomba. :)

(at least I think I get it...)

W.F. Tomba
2005-Feb-23, 05:15 AM
Yeah, that's want I know is right, but my way of thinking is weird. I have to go through every single detail until everything logically makes sense. I get stuck sometimes, obviously. :)
Yeah, I think that way too. It takes a while, but the advantage is once you know something, you really know it.


What you're trying to say is that the chromosomes in each human that are labeled as the "female portion" and the "male portion" only came from a female or male, and that the actual chromosome is not fundamentally different? I think I'm getting it now.
Well, presumably they're somewhat genetically different, but I don't think they differ in any way that depends on the sex of of the parent they came from. (Keep in mind that I'm not an expert and it's been a while since I studied this, so I can't guarantee I'm not forgetting something.)

The X and Y chromosomes are a good example, actually. The female inherits an X from each parent, so the egg's X could have come from either a male or a female parent. But the sperm has either an X from the female parent or a Y from the male parent. If a sperm with a Y could only fertilize an egg with a "female" X, then it would be impossible for sex-linked traits to be passed down from male to female to male, and I know that's possible.

So yeah, I'm fairly certain that which parent a chromosome came from has no bearing on the reproductive process at all.

Disinfo Agent
2005-Feb-23, 01:25 PM
I have a question about meiosis.

Ok, let's say there is a female and her egg cells are dividing through
meiosis. Independent assortment occurs and the homologous chromosomes
are split and each half enters one of the two cells that form as a
result of the first division. Homologous chromosomes are made up of a
male component and a female component (I think), so let's say that all
of the female components of the homologous pair go into one of the
divided cells. Wouldn't it have to find a male sperm with exclusively
male components in order to be fertilized?
I think you're making some sort of confusion, here.

1) IIRC, meiosis produces 4, not 2 cells (the chromosomes divide twice).

2) Meiosis occurs in the reproductive organs of male and female organisms, when the gametes are being formed. It does not occur during fertilisation.

3) Individual chromosomes do not have a sex, although they do determine sex collectively (44 autosomes + two X chromosomes -> female; 44 autosomes + one X chromosome + one Y chromosome -> male).

Edited to make additions and corrections.

N C More
2005-Feb-23, 10:29 PM
Disinfo Agent is correct. Generally confusion exists between meiosis and mitosis. Meiosis differs from mitosis primarily because there are two cell divisions in meiosis, resulting in cells with a haploid number of chromosomes. It's strictly involved in gamete formation. Fertilization is a whole other process.

W.F. Tomba
2005-Feb-23, 11:21 PM
Disinfo Agent is correct. Generally confusion exists between meiosis and mitosis. Meiosis differs from mitosis primarily because there are two cell divisions in meiosis, resulting in cells with a haploid number of chromosomes. It's strictly involved in gamete formation. Fertilization is a whole other process.
But if you start with the assumption that chromosomes have a sex (which they don't), and that every diploid individual has one male and one female chromosome in each pair (which is a misunderstanding of a true statement about the origins of an individual's chromosomes), then you come to the conclusion that the way chromosomes are sorted during meiosis severely constrains the conditions under which fertilization is possible.

The conclusion is wrong, but the reasoning was correct and he wasn't confusing meiosis with mitosis or with fertilization. He was just starting with some incorrect assumptions.