Punnett Square Practice

Directions: For problems 1-5 complete a Punnett square and indicate phenotype and genotype ratios of offspring.

  1. In silkworms a single gene determines the color of the cocoon. The yellow cocoon allele is dominant. It is indicated by "C". The white allele is recessive, and indicated by "c". Use a Punnett square to show cross of a homozygous dominant male (CC) and a homozygous recessive female (cc).
  2. The length of fur in guinea pigs is controlled by a single gene. The dominant allele "F" produces short fur. The recessive allele "f" produces long fur. Use a Punnett square to show cross of a heterozygous male (Ff) and a homozygous recessive female (ff).
  3. In mice a single gene determines the color of the eyes. The black eyes allele is dominant. It is indicated by "E". The red allele is recessive, and indicated by "e". Use a Punnett square to show cross of a heterozygous male and a heterozygous female.
  4. Black fur (W) is dominant over white fur (w) in guinea pigs. Use a Punnett square to show cross of a homozygous black guinea pig with a homozygous recessive guinea pig.
  5. In humans, a cleft chin (C) is a dominant allele. Use a Punnett square to show a cross between a woman with the genotype Cc and a man with genotype cc.
  6. This problem is very tedious to solve with Punnett squares. The polled (hornless) trait (P) in Hereford cattle is dominant; the horned trait (p) is recessive. Use this data to ascertain the genotypes of these four parents.
    1. a polled bull __________ is mated with three cows.
    2. cow A __________ , which is horned produces a polled calf __________ .
    3. cow B __________ , also horned, births a horned calf __________ .
    4. cow C __________ , which is polled produces a horned calf __________ .