Chapter 14 Guide
1. Use the following terms to describe Mendel’s work with his garden peas and his subsequent discoveries regarding inheritance.
True-breeding (purebred), hybrid, segregation, alleles, independent assortment, homozygous, P generation, phenotype, dominant, F1 generation, heterozygous, recessive, trait, genotype, F2 generation.
2. What is the difference between a monohybrid and a dihybrid cross?
Complete the following monohybrid crosses. Give the genotypic and phenotypic ratios. Use Mendel’s pea characteristics (p. 250) to determine dominant & recessive traits.
3. Cross two plants that are heterozygous for green pods.
4. Cross a plant that is heterozygous for axial flowers with a plant that has terminal flowers.
5. Cross a homozygous tall plant with a short plant.
6. Cross a plant that is heterozygous for inflated pods with a plant that has constricted pods.
7. When a tall plant is crossed with a short plant, some of the offspring are short. What are the genotypes of the parents and the offspring? What is the phenotypic ratio in the offspring?
8. Three-fourths (3/4) of the plants produced by a cross between two unknown pea plants have axial flowers and ¼ have terminal flowers. What are the genotypes of the parents?
9. What cross would result in ½ of the offspring having green pods and ½ of the offspring having yellow pods?
10. Summarize ALL possible monohybrid crosses when one trait is dominant and one trait is recessive.
11. What is a testcross? Why are testcrosses useful in genetic study?
12. In fruit flies, longs wings (L) are dominant to short wings (l). In the following experiments, parents of known phenotypes but unknown genotypes produced the listed offspring. Give the most probable genotype for each parents.
Phenotypes
/ Long Wings / Short Wings /Parental Genotypes
Long wings x short wings / 124 / 121Long wings x long wings / 51 / 16
Short wings x short wings / 0 / 82
Long wings x short wings / 34 / 0
13. In humans, normal pigmentation is due to a dominant gene, A. Albinism, lack of pigment, is due to a recessive gene, a. An albino man marries a normally pigmented woman. They have 9 children, all of which are normally pigmented. What are the genotypes of the parents and the children?
14. A normally pigmented man whose father was an albino marries an albino woman, both of whose parents were normally pigmented. They have three children, two normally pigmented and one albino. List the genotypes of the grandparents, parents, and children.
15. A brown rabbit that is crossed with a silver-blue rabbit produces all brown offspring. When these F1 rabbits were crossed among themselves they produced 47 brown animals and 15 silver-blue animals in the F2 generation. Which of these characteristics is dependent on the dominant gene? What is the phenotypic ratio of the offspring in the F2 generation?
16. How many of the brown rabbits in the F2 generation in the previous problem would be expected to be homozygous?
17. In guinea pigs, short hair (F) is dominant to long hair (f). The parents of a long haired pig were both short haired. The long haired pig mates with a short haired pig whose father was short haired and whose mother was long haired. They have one baby pig that is longhaired. What are the most probable genotypes of the pigs mentioned?
18. In dogs, wiry hair is due to a dominant gene and smooth hair is due to a recessive gene. Two wire haired dogs produce a puppy with wiry hair. What kind of female should this wiry puppy be mated to in order to determine if he carries the recessive gene?
Complete the following dihybrid crosses. Give the genotypic and phenotypic ratio.
In mice, the coat color black (B), is dominant to the coat color brown (b). The ability to run, (R, is dominant to the allele for waltzing (r. Waltzing is just going around in circles.
19. Cross a homozygous black, homozygous running mouse with a brown, waltzing mouse.
20. Cross a heterozygous black, homozygous running mouse with a heterozygous black, waltzing mouse.
21. Cross a brown, homozygous running mouse with a heterozygous black, heterozygous running mouse.
22. Cross two brown, waltzing mice.
23. Cross two heterozygous black, heterozygous running mice.
24. If two black, running mice are mated and all of the offspring are black, but half can run and half are waltzing, what are the probable genotypes of the parents?
In horses, black is dependent upon a dominant gene (B), and chestnut color upon its recessive allele (b). The trotting gait is due to a dominant allele (T), the pacing gait to its recessive allele (t).
25. If two black, pacing horses are mated and have 4 offspring, all of which are black and trotting, what does that reveal about the PROBABLE genotypes of the parent horses?
26. What is the chance that two chestnut, pacing horses will have a black offspring?
27. A stud is black and trotting. He is mated to a mare who is also black and trotting. Their colt is black and pacing. The same stud is mated to a second mare who is chestnut and trotting. Their colt is chest and trotting. What is the probable genotype of (A) the stud (B) Mare 1 (C) Colt 1 (D) Mare 2 (E) Colt 2