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Question about sexes and gene

Genetics as it applies to evolution, molecular biology, and medical aspects.

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Question about sexes and gene

Postby f24u7 » Tue Feb 16, 2010 9:23 pm

Is there a different gene controlling the fitness of human body in different sexes? that is to say if i select a short ugly men and reproduce with a tall beautiful women, will i end up with equal amount of short ugly women and tall beautiful women, because the determined gene of human fitness between sexes are the same, or will i end up with tall beautiful women and short ugly men because the determined gene for different sexes is different,

and if the first scenario is true, will the situation change if i continue the selection of short ugly men and tall beautiful women for several generations?
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Postby JackBean » Wed Feb 17, 2010 8:50 am

You should maybe first refer to Southern Elephant Seal. Seal´s males can grow up to 4 tons, whereas females are only up to 900 kg. That is because the males have several females and have to fight for them.
You can find something similar at gorillas. The males are bigger again, because they have to figth for females.
On the other hand, I think, bonobo has no sexual differences, because they do not fight for females.

And back to human. We are something between. The difference is not so big like at gorilla or even the seal, but there are some slight differences, because historically most of our societies did tolerate or prefer, when man had more women.
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Postby biohazard » Wed Feb 17, 2010 10:23 am

I think you may have missed the point a bit Jack (unless I managed to do it myself!)

I think the original poster was interested more about what is the outcome of this kind of "breeding program", not why men are bigger :)

Anyways, in humans the genes for height are inherited from both parents (so it is not sex linked), so a tall woman and a short man would have mostly average sized offspring and some taller and some shorter than average, pretty much in a Gaussian way as far as I know. Other (sex-related) genes then make men to grow taller than women, on average, which would be the case also in this hypothetical example. In other words, a tall man and a short woman would have approximately similar children than a tall woman and a short man. Also, if both of the parents were mid-height, the situation would still be largely the same. It would be considerably different only if both of the parents were tall or short - then the likeliness of tall and short offspring would be greater. Height is not controlled by a single gene, though, so the above example was a simplification, but the general idea remains the same.

What comes to ugliness. Well, that would be bit more difficult to measure due to even more variables it includes, but again, the general idea is quite the same: a beautiful woman and an ugly man would be likely to have "average" children, and among them maybe one beautifyl and one ugly.

If you kept breeding your humans (e.g. tall handsome offspring would have children with other tall handsome people and short ugly ones would mate with short ugly ones), you'd eventually end up having a tall handsome breed and an ugly short breed of humans.

And finally, things like health and nutrition affect the final height of a person, so my examples are valid if the nutrition and health of the people are about the same. Even a person with "tall genes" can remain average if he for example is constantly malnourished as a kiddo.
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Re:

Postby f24u7 » Wed Feb 17, 2010 8:36 pm

biohazard wrote:I think you may have missed the point a bit Jack (unless I managed to do it myself!)

I think the original poster was interested more about what is the outcome of this kind of "breeding program", not why men are bigger :)

Anyways, in humans the genes for height are inherited from both parents (so it is not sex linked), so a tall woman and a short man would have mostly average sized offspring and some taller and some shorter than average, pretty much in a Gaussian way as far as I know. Other (sex-related) genes then make men to grow taller than women, on average, which would be the case also in this hypothetical example. In other words, a tall man and a short woman would have approximately similar children than a tall woman and a short man. Also, if both of the parents were mid-height, the situation would still be largely the same. It would be considerably different only if both of the parents were tall or short - then the likeliness of tall and short offspring would be greater. Height is not controlled by a single gene, though, so the above example was a simplification, but the general idea remains the same.

What comes to ugliness. Well, that would be bit more difficult to measure due to even more variables it includes, but again, the general idea is quite the same: a beautiful woman and an ugly man would be likely to have "average" children, and among them maybe one beautifyl and one ugly.

If you kept breeding your humans (e.g. tall handsome offspring would have children with other tall handsome people and short ugly ones would mate with short ugly ones), you'd eventually end up having a tall handsome breed and an ugly short breed of humans.

And finally, things like health and nutrition affect the final height of a person, so my examples are valid if the nutrition and health of the people are about the same. Even a person with "tall genes" can remain average if he for example is constantly malnourished as a kiddo.
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Postby JackBean » Thu Feb 18, 2010 7:46 am

biohazard: I don't think so. If there is preference for higher men and smaller women, the genes don't have to be located on sex-chromosomes, but still are related to either of sexes.
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Re:

Postby biohazard » Thu Feb 18, 2010 10:06 am

JackBean wrote:biohazard: I don't think so. If there is preference for higher men and smaller women, the genes don't have to be located on sex-chromosomes, but still are related to either of sexes.


That is true. But the point is that the genes that determine the maximum human height are the same in both sexes and a man can receive tall genes from his mother just as he could from his father. So you could get tall men simply by selecting taller women for mothers even though the fathers were average in height.

The original post is a bit ambiguous though. It asks whether the genes for human fitness are different in each sex, and uses beauty and height as ways to measure this. The genes directly affecting these are not sex-related, but some of the genes that influence the final outcome (e.g. effects on androgen hormon production) are sex-linked. So the answer would be yeas and no, depending on how one interpretes the question :)

I just didn't quite get it how fighting elephant seals answer the question in the original post: in animals there surely are size (or fitness) differences between the sexes, which in some cases are huge - and they are related to physical competition in order to get the ladies. But elephant seals do not answer the question what kind of offspring do tall beautiful women and short ugly men have! :wink:

Anyway, I wasn't going to trash your answer or anything, maybe I'm just viewing this topic from a different angle than you :mrgreen:
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Re: Question about sexes and gene

Postby JackBean » Thu Feb 18, 2010 5:06 pm

f24u7 wrote:Is there a different gene controlling the fitness of human body in different sexes?


Just forget about the rest for a while. What is the answer? I think I have answered that, haven't I?
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Re:

Postby f24u7 » Thu Feb 18, 2010 5:31 pm

biohazard wrote:
If you kept breeding your humans (e.g. tall handsome offspring would have children with other tall handsome people and short ugly ones would mate with short ugly ones), you'd eventually end up having a tall handsome breed and an ugly short breed of humans.

And finally, things like health and nutrition affect the final height of a person, so my examples are valid if the nutrition and health of the people are about the same. Even a person with "tall genes" can remain average if he for example is constantly malnourished as a kiddo.



the system delete my last reply.......


so going back to my question, the gene that control facial beauty and height of human is not sex distinctive right ? So even if i continue to breed ugly short men with tall beautiful women for several generation i'll always get the same number of tall beautiful women, short beautiful women, tall ugly women, short ugly women, tall handsome man, short handsome man, tall ugly man, short ugly man?

And the only way to change this, that is if i want the offspring of ugly short man and tall beautiful woman to be all short ugly man and tall beautiful woman is through mutation?
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Postby JackBean » Thu Feb 18, 2010 6:32 pm

I don't think so. If will you allow to breed only short men and tall women for many generations, you should get population of short men and tall women...
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Re:

Postby biohazard » Tue Feb 23, 2010 9:12 am

JackBean wrote:I don't think so. If will you allow to breed only short men and tall women for many generations, you should get population of short men and tall women...


My point is/was that if you breed tall women and short men you have average heigth offspring, on average. That is, the height genes are not sex-related. Other genes then fine-tune the height to be "male height" or "woman height". But a tall man can get these genes from his mother just as well as from his father.

If you always selected short men and tall women, I think you would probably end up with a breed of humans that have very low testosterone levels - that would reduce the height of men (since testosterone is one of the reasons men become bigger than women), but not much of the height of women because their height depends little on testosterone. So both men and women would eventually have "short growth" testosterone levels, but it would only be visible in men.
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Postby JackBean » Tue Feb 23, 2010 9:48 am

Let's turn to the seal for a moment.

Do you agree, that at seals, the genes for size are sex-related, although probably not on sex chromosomes?
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Postby biohazard » Tue Feb 23, 2010 1:31 pm

I do agree.

And apparently I have not been too clear about my terms: with sex-related I have meant X/Y-linked genes. I belive that the underlying mechanisms controlling the size of both seal and human sizes are quite the same - just way much more extreme in seals.

For simplicity's sake let's imagine humans and seals have SIZE gene that determines how tall they can be. This is not X/Y-linked and is inherited from both parents. So an offspring is either SIZE/SIZE, SIZE/size or size/size depending on their parents and chance. This is not sex-linked. Then humans and seals have genes that dictate certain hormonal etc. functions. Let's call these GROWTH genes. Now, likewise, the offspring (both male and female) get either a GROWTH/GROWTH combination or some other allele pair. But, an individual may also get a gene TESTICLE, which comes in the Y chromosome. And if the individual gets TESTICLE (and thus becomes male), his GROWTH gene gets upregulated much much more than in females, and thus GROWTH allows the individual to fully develop his SIZE potential. And seal males get much more TESTICLE effect than human males because of their habit to fight over the females, thus becoming very large.

Therefore, as far as I know, sex does not affect the inheritance of SIZE and GROWTH genes, thus tall women can produce tall male offspring. But if you keep selecting short men, you may end up having a population with very low TESTICLE levels, which mostly means that the men do not reach their SIZE potential :D

The big picture is of course more complex in humans and seals, but I hope that example made clear what I tried to say 8)
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