SBI3U: Dihybrid Cross and Pedigree Worksheet
1. In guinea pigs black hair color is dominant to white and short hair is dominant to long. Cross a homozygous short haired white guinea pig with a homozygous long haired black guinea pig. What are the phenotype and genotype ratios of the F1 and F2 generations? What are the phenotypes of the F2 generation?
2. In horses, black coats and trotting gait are dominant while the recessive alleles are white and pacing gait. If the male is homozygous for both dominant traits, what is the genotype of the male? Cross the homozygous male with the homozygous recessive female. What are the phenotypes and their ratio in the F1 and F2 generations?
3. In snapdragons, the inheritance of flower color and size of leaves are examples of codominance. When red flowered plants are crossed with white, the result is pink. Similarly, when plant with broad leaves are crossed with plants having narrow leaves, the offspring have intermediate leaves. Cross a homozygous red-flowered, broad- leaved plant with a homozygous white-flowered, narrow-leaved plant What kind of offspring are produced in the F1 generation? What are the phenotypes and their ratio in the F2 generation ?
4. If a pure variety of peas showing the dominant characteristics tall, axial flower position and blue flowers is crossed with a variety showing the recessive characters dwarf, terminal flower position and white flowers and the resulting trihybrids are allowed to self-fertilize, what is the expected visible ratio among the offspring of both generations ? What are the phenotypes of both generations ?
5. Within tribble populations coat texture (stiff bristles verses soft short fine hair) and toe type (clawed verses no claws) are autosomal genes. As a geneticist, you are doing the following cross: male parental phenotype is soft, short fine hair and no toe claws; female phenotype is stiff bristles and clawed toes. In looking at the offspring of these matings, you find that all F1 are phenotypically stiff bristled and have clawed toes. Were the parents or homozygous? Which are dominant alleles? If you now mate males to females within the F1 generation, what would you expect the phenotype ratio to be?
6.
I
12
II 1 2 4 5
3 67 8
III
1 2 3 4 5
1. Which members of the family above are afflicted with Huntington’s Disease? ______
2. There are no carriers for Huntington’s Disease- you either have it or you don’t.
With this in mind, is Huntington’s disease caused by a dominant or recessive trait? ______
3. How many children did individuals I-1 and I-2 have? ______
4. How many girls did II-1 and II-2 have? ______How many have Huntington’s Disease? ______
5. How are individuals III-2 and II-4 related? ______I-2 and III-5? ______