Mendelian Genetics Quiz

PLSC 631 - Intermediate Genetics

Mendelian Genetics Quiz

1. Corn seeds can be either yellow or purple. A series of crosses were made, and the following ratios were observed: Cross 1: yellow x yellow = All yellow; Cross 2: purple x purple = All purple; Cross 3: purple x yellow = 1 purple:1 yellow; Cross 4: purple x purple = 3 purple:1 yellow. 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. Curly wing is a mutant of Drosophila. To study the genetics of this trait crosses were made among Curly flies. The following ratio was observed:1022 Curly: 498 normal wing. Will the Drosophila geneticists successfully create purebred Curly? Why or why not? Create your own gene symbols to use in your discussion.

3. Some plants can have colorless, red or purple flowers. This is the result of a biochemcial pathway in which the red color is produced from a colorless pigment and the purple pigment arises from the red pigment. Two purple plants were crossed and the F₂ contained 181 purple plants 59 red plants and 83 colorless plants. From these results, what can you conclude about the genetics of color in these plants? Include in your discussion, a list of the genotypes from each generation.

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 two mice heterozygous at all three of the 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.)