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amayabrianna
amayabrianna
Student
Community / Jr. College

Any help please!!! I can not figure this out. made Punnett squares for all and only one that I can get is Tt, Tt. Not an option in my book though!!!

A recessive allele t is responsible for a condition called distornia.  A man who has this condition marries a woman who doesn't.  One of their 4 children has the condition.  What are the possible genotypes of the man and the woman? (to help answer this question, create a Punnet square for each possibility)

The father is Tt; the mother is TT

The father is tt; the mother is TT

Both parents are TT

The father is tt; the mother is Tt

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Posted by amayabrianna on Tuesday November 10, 2009 at 11:53 AM and tagged with biology, genetics, punnett square, science.

Answers:


  1. pohnpei397 Teacher
    Community / Jr. College

    eNotes Editor

    Your answer of Tt, Tt can't be right because the man has to have the condition.  If he has it, he must be tt.

    The correct answer here is that the father is tt and the mother is Tt.  Here's why:

    We know he has to be tt so that he can have the condition.  But if she is TT, no children can possibly have the condidion.  So therefore, she must be Tt.

    I asssume you didn't like that answer because your Punnett squares tell you that two of their kids should be tt if the are tt,Tt.  But the thing is that two of them don't HAVE to have it.  Punnet squares are just a probability thing, not a for sure thing.  Each of their kids had a 50% chance of getting the condition, but only 25% of the kids did get it.

    So, the other three options are impossible, but the fourth is at least possible so it must be the right answer.

    Sources:
    http://anthro.palomar.edu/mendel/mendel_2.htm

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    Posted by pohnpei397 on Tuesday November 10, 2009 at 12:41 PM