need help with some home work

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

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need help with some home work

Post by scoe » Thu Jan 15, 2015 6:55 pm

1. can a man and a woman that are both homozygous for a recessive allele produce a heterozygote baby? I said yes here

2.Can A man and a woman that are both homozygous for a dominant allele produce a heterozygote baby? I said yes here

3. Can A dominant homozygous man and a heterozygous woman produce a recessive baby? I said no here

Can anyone tell me if I am right and Why?

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Post by Athira » Fri Jan 16, 2015 7:33 am

Well,I am sorry to say this-But your first two answers are wrong!

1)See,recessive alleles can be expressed only and only in the homozygous condition.So you need not say specifically 'homozygous' for a recessive allele THAT HAS BEEN EXPRESSED.
For example: Lets say that there is a gene T which codes for the tallness character.So depending on the alleles which have been expressed-the person can turn out to be tall if he has-Tt(heterozygous) or TT(homozygous).-Here T is the dominant trait over t.
whereas the person will become dwarf only if both the alleles for the gene is tt. (I hope this explanation of mine made some sense! ;-))

Hence as answer of your question-there is no question of the baby being heterozygote! The baby WILL HAVE a recessive trait ONLY!
2) If you understood what I said above-then I think you will have answer to the second question as well now! The baby will definitely be homozygous dominant!(because both mom and dad are homozygous dominant for the particular trait)
Notice why I am writing HOMOZYGOUS dominant because the baby can also be HETEROZYGOUS dominant (if it has Tt pair of allele for tall character),but for recessive allele its not the case-it HAS TO BE tt!

3)You are absolutely right!! :-) Tip-You can always make a cross to check if these kind of questions confuse you!
I hope this helps and please feel free to ask me any kind of doubts in this!

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Re: need help with some home work

Post by Youngji » Sun Feb 01, 2015 1:14 pm

I agree with Athira here. Your first two answers are wrong.
You can visualize a cross.
aa x aa will never give Aa genotype for a baby.
AA X AA will never give a Aa baby.
oN THE FACE of it, if you have a parent Aa cross with AA, you should get a baby with either AA or Aa right? However, it is possible to get a baby with recessive phenotype. The answer is yes for the third question too!

This is how it works. uNDER special circumstances, a gene might be influenced by modifications of the histone code and thus the level of expression will be affected. This is called epigenetics, you can read up on it. What happens is that only the gene from the mother or the father is expressed. Here if only the gene from the mother is expressed, then the phenotype of the baby will be just a. Although the baby might be Aa, it does not express the A gene from the father and thus is phenotypically recessive as it only expresses the a gene! It is possible and defects in this system of inheritance can result in disorders such as the Angelman syndrome or Prader–Willi syndrome.

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