Mendelian Genetics Quiz

PLSC 631 - Intermediate Genetics

Mendelian Genetics Quiz

1. Bean leaves can be either pubescent or glabrous. A series of crosses were made, and the following ratios were observed: Cross 1: pubescent x pubescent = All pubescent; Cross 2: glabrous x glabrous = All glabrous; Cross 3: pubescent x glabrous = 1 pubescent:1 glabrous; Cross 4: pubescent x pubescent = 3 pubescent:1 glabrous. Which phenotype is dominant? Create your own gene symbol and give the genotypes of the parents (as close as you can determne) for each cross.

2. Manx is a popular bred of cats because of its unique feature of no tail. As Mendel's laws were becoming understood among cat breeders, they realized they needed to develop pure line Manx cats. But every time they crossed two Manx cats the liters contained tailless and tailed cats. Because they were very good students of Mendel, they counted the progeny of several liters and found that 52 cats had tails and 98 cats lacked tails. At that point they realized it was a futile attempt to try to develop pure bred Manx cats any further. What lead them to this conclusion. Create a set of gene symbols to use when discussing the genotypes of tailed and tailless cats.

3. Phenotypic variation for seed capsule shape in the Shepherd's Plant includes triangular and ovoid shapes. Pure bred parents expressing one or the other shape were crossed and the F₂ generation grown. The ratio was 15 triangule: 1 ovoid. Explain genetically how this result might have occurred. Create gene symbols to use in your explanation when you discuss the phenotypes of the different generations.

4. In mice, a series of five alleles is responsible for fur pattern. The dominance relationship between different alleles is as follows: A^Y (homozygous lethal; yellow fur > A^L (light belly agouti) > A⁺ (agouti) > a^t (black and tan) a (black). The ">" symbol means the allele is dominant to all alleles listed after it. The phenotypes associated with each allele is given in parenthesis. What is the phenotypic ratio from the following crosses. 1. A^YA^L x A^YA⁺ 2. A^Ya x A^La^t 3. a^ta x A^Ya 4. A^La^t x A^LA^L.

5. Coat color in mice requires the action of dominant alleles at three genes, B, T, and A. The B gene converts a tan pigment to black. The tan pigment is generated by the action of the T gene upon a precursor white pigment that is generated by the A gene. Finally, the precursor to that white pigment is a chemically different white pigment. A cross is made between a white mouse homozygous dominant at the A gene and a mouse heterozygous at all three genes. What is the phenotypic ratio of the offspring with regards to coat color? (Hints: 1) Draw out the pathway to better understand the relationship between the genes. 2) Use a Punnett square to help you find your answer.)