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Postby TotallyClueless » Mon Mar 30, 2009 5:40 am

I have a homework assignment. One of the questions is:

"Bob and his father both have polydactyly (an excess number of fingers and toes). The polydactyly trait is controlled by the dominant allele P on one gene. Bob's sister Sue does not have polydactyly. What is Bob's genotype? What is the genotype of Bob's sister? What is Bob's father's genotype?"

I don't get it, and I could use some help. :roll:
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Postby canalon » Mon Mar 30, 2009 4:10 pm

P is the allele for polydactyly and is dominant
p is the wild type allele and is recessive
Now let us consider the phenotype for all possible combination of genes in an individual:
PP would be... (I let you think about it, read the pertinent definitions and fill the blanks)
Pp or pP would be...
pp would be ...
So Bob and his father can have such and such genotype. Assuming Bob's and Sue's Sister are the same and that she is wild type for polydactyly (ie has the traditional number of fingers) her genotype must be ...
Now let us consider the possible outcomes of the marriage of Bob and Sue's parents. I suggest making the Punnet square for both genotype possible for Bob's father. and analyse the phenotype of the possible descent. Only 1 genotype is possible, and it will give you the answer with respect to the 2 kid's genotypes. Good luck.

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