Thursday, November 26, 2009

How does genetics work?

People say brown eyes are dominant but my brother has 4 kids with an asian girl and 2 of them have blue eyes and brownish hair.



How does genetics work?

It is likely that the Asian mother is not 100% Asian. She probably has had a Caucasian ancestor as some point and carries a recessive eye color allele for blue eyes.



How does genetics work?

You get genes from both parents. What dominant means is that it over powers the other gene. The mother of the two blue eyed children got the brown eye gene from of one her parents and the blue eye gene from the other. Since brown is dominant, she has brown eyes. Now all her kids will get either the brown eye gene or the blue eye gene from her and another gene from the father. If the kid gets 2 blue eye genes, then they have blue eyes. It is possible for two brown eyed parents to have blue eyed kids if they carry the blue eye gene because brown is dominant. It is NOT possible for two blue eyed parents to have a brown eyed kids because they do not carry the brown eye gene.



Of course, this is a bit simplified because people have different shades of eye color like green, hazel, etc. Not just blue and brown, but you get the idea.



How does genetics work?

You don't say anything about the hair color or eye color of both parents.



for eye color if your brother and the kids mom both have brown eyes then they each carry one gene for brown and one gene for blue which I will write as Bb (B for brown and b for blue). the kids could get the following combinations of genes...



BB



Bb



bB



bb



Brown eyes are dominant over blue so BB, Bb and bB would be brown and bb would be blue. That's a 1/4 chance of blue eyes and 3/4 chance of brown eyes. If they had a very large number of kids, then you would see that ratio show up.



I don't know the details of hair color, but it's probably pretty similar.



How does genetics work?

Do a search on 'Mendelian inheritance'. Just because a dominant trait is in one or both parents doesn't necessarily mean that that trait will express itself in their offspring. In junior high and high school biology, you figure how traits are passed on through what is known as a 'Punnet square' (although, when I was in school we still called them Mendel Squares).



Recessive traits (such as the blue eyes in your example) may be less likely to be expressed, but it doesn't mean that the genes for those traits are eliminated. It simply means that more of the offspring are likely to have the dominant trait as opposed to the recessive one. Your brother's children having blue eyes is just a statistical fluctuation from what you would expect from four children, which would be three brown-eyed kids and one blue-eyed. It's also possible that the mother has genes for blue eyes in her genetic makeup, even though they are not expressed in her.



Genetic inheritance is a very complex field of study. There is a public misconception that there is one gene for each trait (a gene for eye color, another for height, etc.), when in reality, the genes work with each other in complex interactions to determine the makeup of the offspring.



How does genetics work?

genetics doesn't WORK-----genetics is the study of the genes of animals or people(or plants).You aquire 1/2 of your genes from your mother and 1/2 from your father.Genes are made up of pairs of chromosomes,in different sequenses,which in turn determine the outward apperance of the final product.There are always dominant and recessive genes.you can work the outcome with a ''chi'' square.

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