Gender Ratios.

dragon(ele)nerd

dragon(ele)nerd

Well-Known Member
Hey everyone,

Like to get people's thoughts on some animal gender ratios. I know mostly it is 50/50 chance at births. But in particular species it apparently leans towards one gender sometimes. In some cases as much as 30/70! This is according to a biology teacher in my school. Is this true.
I know some species have a shortage of some genders due to humans e.g. there is massive difference between cows and bulls in elephants of both species due to mass poaching. With global warming though in some few years there will be a distinct shortage of females in reptiles. As temperature determines the sex in reptiles for most of the time.

q's and comments please.
 
dragon(ele)nerd said:
With global warming though in some few years there will be a distinct shortage of females in reptiles. As temperature determines the sex in reptiles for most of the time.
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Only some reptiles are temperature-determined-sex. Most of them are not.

:p

Hix
 
I don't think any of the snakes are TSD. But all the crocodiles, turtles and some lizards are.

:p

Hix
 
thought as much, thanks. I doubt birds gender's are determined by temperature. A teacher said this to me.
 
I've heard that the chances of humans coming out as boys or girls has a little to do with temperature (cold for boys, warm for girls), how true this is, I'm not sure.
 
Birds are not temp dependant take for example an incubator full of hen eggs, they are all incubated at the same tempreature but you will still get a healthy mix of hens and roosters. It is an interesting topic sex ratio, some animals in captivity have high birth rates of one sex or another and it is believed it is due to stress hormone levels during the pregnancy. males are more likely to disprese away from the stress factor hence the high birth rate of males. It is interesting to note that there is a much greater chance of pygmy hippo calves to be born female! males are becoming a bit of a rarity now.
 
well apparently most species are programmed to give birth to slightly more females!
the human population stands at 48% male and 52% female.
 
I know the gender ratio for humans at birth differs in nations, but for Czech republic it´s currently 106 boys for each 100 girls. But due to a higher mortality of men during their whole live the population is skewed toward women.

Studies of wild populations of deer, macaque etc. (and human too) showed that stressed and/or malnoultrished females give birth more offen to girls, relaxed females in an excellent condition have higher change to have a boy. The same goes for their status in the hierarchy - those on highest rank have got more sons, those on the bottom have got more daughters.

There are other factors that can change the gender ratio of biths, for example some parasites as Toxoplasma gondii. One study showed that women infected relativelly shortly prior the conception had much more higher possibility to have a boy: around 280 to 100. Or high doses of some hormones can also change the ratio, as progesteron.
 
I not sure about other species but in humans gender is determined by the sperm, with male sperm swimminly extremly fast but die quickly and female sperm slow but have a longer lifespan.
 
dragon(ele)nerd said:
I not sure about other species but in humans gender is determined by the sperm, with male sperm swimminly extremly fast but die quickly and female sperm slow but have a longer lifespan.
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The human species has a higher birth rate of males because of the Y chromosome. This doesn't not have back up copies of the gene and therefore leads to higher deaf rate in males.

It also explains why only male can be colour blind.
 
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