Malaysia Veterinary Forum (Archive)

Mytaninn · Joined: 16 Dec 2005 Posts: 28

Dear Dr,

I have some question in my mind about the egg development, but not sure where to start looking for the answer.

The question that I would like to searh for the answer is the eggs development and how it relate to the sex of avian species.

I believed that avian sex (eggs) is not related to the temperature of the incubation process but is 'decided' before it is laying. (Please correct me if I am wrong). If this is the case, at which stage the sex of the offsping will be 'decided' and what will play the role (that will effect it)?

Thank you and best regards...

p/s: If there is any book that mention about this, please let me know the title and where to get it. Thanks.

Dr Chong · Joined: 12 Dec 2005 Posts: 666 Location: KL

I'm not expert in birds. But I think the sex of the bird is determined at the time fertilization is occurred, meaning that at the time when the sperm fertilized the ovum. It's analogous to human. In human, when a sperm (spermatozoon) carrying an X sex chromosome fertilizes an ovum (that always carries X sex chromosome) the resulted XX pair will give you a baby girl. Let's say a spermatozoon that carrying an Y sex chromosome fertilized an ovum, the XY pair will give you a baby boy.

In birds, it's somehow the other way round, where males are homogametic (ZZ) and females are heterogametic (ZW). However, it's not clear whether it is the presence of the W sex chromosome that triggers female development, or the dose of the Z sex chromosome that confers male development in birds, or both could be important in gender determination.

Although common in reptiles, incubation temperature has not been considered to be a factor in determining gender in birds.

Mytaninn · Joined: 16 Dec 2005 Posts: 28

Thank you Dr,

The reason that I ask is because of Robert Black's Articles which tell about the effect of ultraviolet lighting toward the sex of the offspring.

Based on the article, the breeding pair that has been exposed to ultraviolet light will have more male (which is about 50% of the offspring) compared to breeding pair that didn't exposed to ultraviolet light. I understand that he do the experiment on indoor facilities.

Co-incidently, a friend of mine who bring up this topic admit that comparatively he get more male this season(50% of the offspring) because the weather in his place is good and got lots of sun light compared to last year weather which is not so good (not many sunlight and always rain) which he get only about 30% male.

Based on your explaination about ZZ and ZW chomosome. Do you think that there is any possibilities that when the breeding pair is exposed to ultraviolet light or more sunlight, the body of the female or male bird will trigger the Z chromosome to be more active and therefore the pair will produce more male offspring?

p/s: sorry to ask a lots of question, I found that this is very interesting and I am very keen to know more about this 'secret' of the nature. It make aviculturist more interesting :D

Dr Chong · Joined: 12 Dec 2005 Posts: 666 Location: KL

I've also found articles saying that some other factors (dietary, environmental, etc.) can influence or change the gender ratio in birds. Personally, I do think it's possible by manipulating those factors but it's a bit different from that in the reptiles. I think it's more on influencing the parents in producing their sex cells. With the cells carrying the Z or W chromosomes predominate, you'll get a tilted ratio of genders produced. So, back to the same question, the sex of the bird is still determined at time of fertilization.