## Mendel crossing with 4 characteristics

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

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tomkoolen
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Posts: 2
Joined: Wed May 22, 2013 9:37 pm

### Mendel crossing with 4 characteristics

Hello everyone,

I am having some trouble with the following question:

2 organisms are crossed with the following genotypes: AaBbCcdd x aaBbCcDd
a) What is the probability for a descendant to be homozygous recessive for all characteristics?
b) What is the probability for a descendant to be homozygous dominant for all characteristics?

I believe that question b can be solved by noticing that the second parent does not have allele A which makes it impossible => P = 0. However for question a, I cannot deduct a similar answer because both parents have at least one recessive allele for each characteristic. Is it really necessary to create a Punnett square for this problem or is there an easier way to solve this?

Tom Koolen

Cat
King Cobra
Posts: 635
Joined: Thu Feb 14, 2008 7:40 pm

### Re: Mendel crossing with 4 characteristics

tomkoolen wrote:Is it really necessary to create a Punnett square for this problem ...?

YES.

phanhuyen
Garter
Posts: 1
Joined: Wed Jul 24, 2013 12:52 pm
salute you. according to me is the b you are right to do so.
questions a)
the genotype of the descendants I will give the allele ratio
1/2a: 1/2b: 1/2 c: 1d
published in the 1a: 1/2 b: 1/2 c: 1/2d
Thus genotype probabilities in descendant aabbccdd = (1/2 x 1/2 x 1/2 x 1) x (1 x 1/2 x 1/2 x 1/2) = 1/64