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Genetics problems

3. The urine of some people has a distinctive odor after eating asparagus. This appears to be a recessive trait. If a person with aromatic urine marries a person heterozygous for this trait, what phenotypic and genotypic ratios will their children theoretically exhibit?

4. Cat's tail has 42 chromosomes in each somatic cell.
A. How many tetrads will be present at metaphase I of meiosis?

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3. The urine of some people has a distinctive odor after eating asparagus. This appears to be a recessive trait. If a person with aromatic urine marries a person heterozygous for this trait, what phenotypic and genotypic ratios will their children theoretically exhibit?

Response:

"Aromatic" means having a strong odor. Therefore, the person with aromatic urine must be "aa" because the trait is recessive. In order for him to express the trait, he must have both recessive alleles. Clearly, the person he marries is heterozygous, "Aa." So, we do the cross:

aa x Aa

First, we must figure out what gametes each parent will produce:

aa can make only 1 gamete type: a
Aa can make 2 gamete types: A and a

Therefore, here's the Punnett Square:

A a
a Aa aa

This shows us that the expected genotypic ratio of children is 1 Aa: 1 aa. Another way to say this is that 50% will be Aa and 50% will be aa.

What does this mean phenotypically? It means that 50% will be normal (Aa) and 50% will have aromatic urine (aa).

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4. Cat's tail has 42 chromosomes in each somatic cell.

A. How many tetrads will be present at metaphase I of meiosis?

Response: What do we mean when we say "42 chromosomes in each somatic ...

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