Inheritance and sex


What are phenotype ratios in F1 generation of fruit flies when a red-eyed female is crossed with a white-eyed male and on other side, a white-eyed female is crossed with a red-eyed male?


    In cats, dominant allele of gene Y (in homozygote form in females and hemizygote form in males) determines black color of fur. Recessive allele determines yellow color and heterozygote females have tortoise-colored fur.
  1. What type of inheritance is it? On which chromosome is gene for fur color located?
  2. Black female has one tortoise-colored and four black offspring. What genotype and color of fur does their father have? What sex and color does the black offspring have?
  3. Tortoise-colored female was mated with yellow male. What is probability that they will have yellow male and female offspring?


Daltonism (color blindness) is disease with recessive X-linked inheritance. A couple has daughter with daltonism, but her mother is able to distinguish colors.

What genotypes do parents and their daughter have?


Haemophilia is disease with a recessive gonosomal inheritance linked to chromosome X. A man with haemophilia has daughter with healthy woman with homozygote genotype.

What genotype does their daughter have?


    The color of Ayrshire cattle is determined by gene M. Cattle and bull with genotype MM are mahogany, cattle with recessive homozygote genotype is red spotted. The bull with genotype Mm is mahogany, while the cattle is red spotted.
  1. What type of inheritance is it?
  2. The red spotted cattle (her father was mahogany) was mated with the red spotted bull. What are genotypes and phenotypes of parents and their offspring?
  3. What is the phenotype ratio in F2 generation?
  4. The mahogany cattle gave birth to red spotted offspring. What is the sex of offspring?


    In humans, there is gene P for baldness (hairlessness). Men with genotype PP and Pp are bald, while women are bald only with genotype PP. Gene B determines color of eyes; brown one is dominant over blue one.
  1. What type of inheritance does hairlessness show?
  2. The hairless man with brown eyes (his father has hair and blue eyes) married a blond woman with blue eyes (her father and brothers were bald). What color of eyes can they expect in their children? Will they have hair or will they be bald?


    In Siamese fighting fish (Betta splendens), dominant allele of gene Z induces enlargement of fins, if there are male sex hormones presents.
  1. What type of inheritance is it?
  2. What type of fins can we expect in offspring resulted from crossing: Zz x Zz.
  3. How can you identify genotype of male with enlarged fins and genotype of female, if you have recessive homozygotes for crossing?