MONOHYBRID and DIHYBRID GENETIC QUESTIONS

Monohybrid Crosses:

1. An allele for brown eyes B is dominant over that for blue eyes b. A couple of whom one is brown-eyed and the other blue-eyed have eight children, all brown eyed. What would be the genetic make up of each parent in this regard? For each parent state whether they are homozygous or heterozygous.


2. A blue-eyed man, both of whose parents were brown-eyed, marries a woman. They have one child who is blue-eyed. What are the genotypes of all the individuals mentioned?


3. A brown-eyed man whose father was brown-eyed and whose mother was blue-eyed married a blue-eyed woman whose father and mother were both brown-eyed. The couple has a blue-eyed son. For which of the individuals mentioned can you be sure of the genotype? What are the genotypes? What genotypes are possible for the others?


4. A hybrid pink snapdragon was crossed with a pure white one. Red flower colour is incompletely dominant. Make a diagram to show:

* the gene constitution of the parents
* genotypic and phenotypic ratios of the F1 generation]




Dihybrid Crosses:



1. In the garden pea, Mendel found that yellow seed colour was dominant to green and round seed shape was dominant to shrunken. Determine the phenotypic and genotypic ratios for the F1 generation and the phenotypic ratio for the F2 if a plant with homozygous rounded yellow seeds is crossed with a plant with shrunken green seeds.


2. Tall tomato plants are produced by the action of a dominant allele T and dwarf plants by its recessive allele t. Hairy stems are produced by a dominant gene H and hairless stems by its recessive allele h. A dihybrid tall, hairy plant is crossed with a dwarf hairless tomato plant. Determine the phenotypic ratio for the F1 generation.




3. Black coat colour in Cocker Spaniels is dominant, while red coat colour is recessive; solid pattern is dominant, while spotted pattern is recessive. A solid black male is mated to a solid red female and produces a litter of six pups: two solid black, two solid red, one black and white, and one red and white. Determine the genotypes of the parents.