Mendelian Genetics Quiz

PLSC 631 - Intermediate Genetics

Mendelian Genetics Quiz

1. Pigeons can be either plain or checkered color. A series of crosses were made, and the following ratios were observed: Cross 1: Plain x Plain = All Plain; Cross 2: Checkered x Checkered = All Checkered; Cross 3: Checkered x Plain = 1 Checkered:1 Plain; Cross 4: Checkered x Checkered = 3 Checkered:1 Plain. 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. In a population of foxes being bred for fur, a new platinum coat color was detected. Because this color proved to be quite popular, the manager of the farm attempted to develop a pure line of platinum foxes. But every time that two platinum-colored foxes were crossed normal coat colored progeny appeared. After repeatedly trying, the manager looked at his data and saw that he had obtained 81 platinum-colored and 39 normal-colored foxes from these crosses. At this point he realized that his efforts to develop a pure line were futile. What did he observe in his results that lead him to his conclusion. Use your own gene symbols in your explanation.

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^ta x A^Ya 2. A^La^t x A^LA^L 3. A^LA^L x A^YA⁺ 4. A⁺a^t x a^ta.

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.)