Mendelian Genetics Quiz

PLSC 631 - Intermediate Genetics

Mendelian Genetics Quiz

1. Guinea pigs have either white or black coats. A series of crosses were made, and the following ratios were observed: Cross 1: Black x Black = All Black; Cross 2: White x Black = 1 White:1 Black; Cross 3: Black x Black = 3 Black:1 White; Cross 4: White x White = All White. 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. Chickens have been bred for some of their unusual phenotypes. One such phenotype is Creeper in which the bird has shortened legs and appears to "creep" along the ground. Attempts were made to develop pure bred Creepers by intermating among birds with this unique phenotype. Yet each time the cross was made, chickens with normal leg length would appeared. Data was collected from a series of Creeper x Creeper matings, and the segregation ratio was 44 Creeper: 14 Normal. At this point breeders realized it was futile to try to develop pure bred Creeper chickens. What observations lead them to that conclusion. Use your own gene symbols in your explanation.

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

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.)