Genetic Practice Problems

  1. A heterozygous tall plant is crossed with another heterozygous tall plant. In the space provided, identify the parent’s genotype. What percentage of the offspring will be short? What percentage will be homozygous dominant? Write the genotypic ratio. Write the phenotypic ratio.
  1. Round seeds are dominant to wrinkled seeds. A heterozygous round seeded plant is crossed with a homozygous round seeded plant. What percentage of the offspring will be homozygous recessive? Show your work.
  1. In some chickens, the gene for feather color is controlled by co-dominance. The allele for black is B and the allele for white is i. The heterozygous phenotype is known as erminette.
  2. What is the genotype for black chickens? ____
  3. What is the genotype for white chickens? ____
  4. What is the genotype for erminette chickens? ____
  5. If two erminette chickens were crossed, what is the probability that:

a. They would have a black chick? ____%

b. They would have a white chick? ____%

Parents: ____ X ____

Draw the Punnett Square:

  1. A black chicken and a white chicken are crossed. What is the probability that they will have erminette chicks? ____%

Parents: ____ X ____

Prove your answer:

  1. In snapdragons, flower color is controlled by incomplete dominance. The two alleles are red (R) and white (W). The heterozygous genotype is expressed as pink.

a.What is the phenotype of a plant with the genotype RR? ______

b.What is the phenotype of a plant with the genotype WW? ______

c.What is the phenotype of a plant with the genotype RW? ______

  1. A pink-flowered plant is crossed with a white-flowered plant. What is the probability of producing a pink-flowered plant? ____%

Parents: ____ X ____

Prove your answer.

  1. What cross will produce the most pink-flowered plants? Show a punnett square to support your answer.

Parents: ____ X ____

  1. Pretend that Brad Pitt is homozygous for the type B allele, and Angelina Jolie is type “O.” What are all the possible blood types of their baby?
  1. Red-green color blindness (b) is a recessive sex-linked trait. A colorblind male marries a normal female. Their daughter is colorblind.
  1. What are the genotypes of both parents and the daughter?
  1. Can a colorblind father have daughters who are not colorblind? Explain.
  1. If a normal sighted woman whose father was color-blind marries a color-blind man, what is the probability that they will have a colorblind child?
  1. A tall green pea plant (TTGG) is crossed with a short white pea plant (ttgg). Write all the possible gametes for each parent:
  1. A tall green pea plant (TtGg) is crossed with a Short white pea plant (ttgg). Write all the possible gametes for each parent: