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Mendel's Genetics

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I am having trouble with these few sample problems. I really do not understand the concept of Mendel's ideas. Can someone please elaborate? Please see attached file.

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Mendel's genetics basics are explored and explained.

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1. The pattern of coat coloration in dogs is determines by the alleles of a single gene, with S (solid) being dominant over s (spotted). Black coat color is determined by the dominant allele A of a second, independently assorting gene pair, and tan by homozygosity for the recessive allele, a. A female having a solid tan coat is mated with a male having a solid black coat and produces a litter of six pups. The phenotypes of the pups are 2 solid tan, 2 solid black, 1 spotted black. What are the genotypes of the parents?


SS or Ss indicate solid color, whereas ss means spotted. In addition, AA or Aa will produce a black color and aa will produce tan.

Therefore, a solid tan female is S_aa and the solid black male is S_A_. We use an underline to indicate an unknown allele.

Now, since we end up with 2 solid tan pups, we know that the father who we wrote as S_A_ must now be S_Aa. How come? Since some pups are tan, they must be aa. In other go be aa, they must get an "a" from the mother and an "a" from the father.

What else can we learn? One pup was spotted black. Since spotted can only be produced with "ss." we know that each parent must have an "s" allele. Therefore, the mother must now be Ssaa and the father must be SsAa.

2. What is expected probability that is we toss a coin three times, we will get heads all three times? Show work.

Response: The probability of getting one heads in one toss is 0.5. The probability of getting two heads in a row is 0.5 x 0.5. The probability of getting three heads is a row is 0.5 x 0.5 x 0.5. You can do the math.

3. Suppose that gene "d" is sex linked (on the X chromosome), recessive and lethal. A man married a woman who was heterozygous for the gene. If this couple had many normal children, what would be the predicted sex ratio of these children? Show work?

Since the "d" allele is ...

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