Name: ______

Date: ______

Period: ____

Dihybrid Cross Part 1

Objective: Using the steps we have discussed in class, complete the monohybrid cross problems below.

1. Mr. C and Alex both write with our right hands (heterozygous). We also both have brown hair (heterozygous). Predict the offspring from this cross:

  1. What is the genotype of the parents: ______
  2. Set up a Punnet square with possible gametes (genotype):
  1. Fill in the Punnet Square for the resultant offspring.
  2. What is the predicted genotypic ratio for the offspring: ______
  3. What is the predicted phenotypic ratio for the offspring: ______

2. Some plants are tall (dominant) while others are dwarfs (recessive). Some have purple flowers (dominant) while others have white flowers (recessive). Cross a homozygous dominant parent for both traits with a homozygous recessive plant for both traits and determine the possible offspring of the cross.

  1. What is the genotype of the parents: ______
  2. Set up a Punnet square with possible gametes (genotype):
  1. Fill in the Punnet Square for the resultant offspring.
  2. What is the predicted genotypic ratio for the offspring: ______
  3. What is the predicted phenotypic ratio for the offspring: ______

3. Black fur in guinea pigs is dominant while white fur in guinea pigs is recessive. Rough fur is dominant and smooth fur is recessive. Cross a heterozygous parent for both traits with a homozygous recessive parent for both traits and determine the possible offspring of the cross.

  1. What is the genotype of the parents: ______
  2. Set up a Punnet square with possible gametes (genotype):
  1. Fill in the Punnet Square for the resultant offspring.
  2. What is the predicted genotypic ratio for the offspring: ______
  3. What is the predicted phenotypic ratio for the offspring: ______

4. About 70% of Americans get a bitter taste from the substance called phenoylthiocarbamide (PTC). It is tasteless to the rest. The "taster" allele is dominant to non-taster. Also, normal skin pigmentation is dominant to albino. A normally pigmented woman who is a non-taster for PTC has an albino-taster father. She marries an albino man who is a taster, though the man's mother is a non-taster. Determine the possible offspring of the cross.

  1. What is the genotype of the parents: ______
  2. Set up a Punnet square with possible gametes (genotype):
  1. Fill in the Punnet Square for the resultant offspring.
  2. What is the predicted genotypic ratio for the offspring: ______
  3. What is the predicted phenotypic ratio for the offspring: ______