Discussion:
Introductory Genetics Problem Set
1. Two black guinea pigs were mated repeatedly over several years. They produced 29 black progeny and 9 white progeny. Explain these results, giving the genotypes of parents and progeny.
2. In horses, black is dependent on a dominant gene (B) and chestnut upon its recessive allele (b). The trotting gait is due to a dominant gene (T) and the pacing gait due to its recessive allele (t). A homozygous black pacer is mated to a homozygous chestnut
trotter.
A. What is the genotype of the F1 generation?
B. What is the phenotype of the F1 generation?
C. If two F1 individuals were mated, use the fork line method to determine the kinds of offspring (phenotypes) would they have and in what proportions?
D. If an F1 male were mated to a homozygous female black pacer, use the fork line method to determine the genotypes and genotypic ratio of offspring that would be produced?
3. In the cross AaBb X Aabb:
A. How many different genotypes can occur in the gametes of each parent?
B. Give the gametic genotypes and gametic ratios for each parent.
4. Porcupines have a diploid chromosome number (2n) of 34. Considering only independent assortment (the random alignment of maternally and paternally derived chromosomes), how many genetically different offspring are possible when two porcupines mate?
5. A porpoise has a diploid chromosome number (2n) of 44. How many different chromosomal configurations can occur following meiosis?
6. The amount of DNA in a G1 nucleus of the lemur (Lemur catta) is 6.22 picograms (pg). The diploid number of chromosomes in the lemur is 56. What would be the number of chromosomes and the DNA content of a nucleus in each of the following:
Cell Type Number of Chromosomes Amount of DNA (pg)
Lung cell in G2 ________ ________
Mitotic metaphase ________ ________
Second polar body ________ ________
Sperm ________ ________
A secondary oocyte ________ ________
Primary spermatocyte ________ ________
7. A somatic cell in a garden pea (2n = 14) undergoes mitosis.
A. How many chromosomes does each progeny cell have?
B. If a cell in the same plant undergoes meiosis, how many chromosomes does each cell have after the first division?
C. How many chromosomes after the second meiotic division?