Name:_____________________________________  Period:__________

Dihybrid Cross Lab

Key: Each piece of yarn in an egg or sperm represents a gene controlling a trait. The different colors represent different alleles of that gene in the population.

Color

Trait

Dark Blue

Dimples (D=dominant)

Light Blue

No dimples (d=recessive)

Maroon

Freckles (F=dominant)

Red

No freckles (f=recessive)

Dark Green

Able to roll tongue (A=dominant)

Light Green

Not able to roll tongue (a=recessive)

Orange

Free earlobes (F=dominant)

Yellow

Attached earlobes (f=recessive)

 

Directions:

Your lab station contains two eggs and two sperm.

1.      Open each of the eggs and study momís alleles. Separate each of the alleles by trait (color) using the above chart.

2.      Determine momís genotype and phenotype for dimples and freckles. HINT: (Suppose mom has one dark blue and one light blue piece of yarn. She also has one red and one maroon piece of yarn. Dark blue represent dimples (D) and the light blue represents no dimples (d). Maroon represents freckles (F) and the red represents no freckle (f). Momís genotype would be DdFf and her phenotype would be dimples and freckles.)

3.      Next open the two sperm at the lab station and study dadís alleles for dimples and freckles. Determine dadís genotype and phenotype.

4.      Since it is random which sperm will fertilize each egg, a Punnett square will allow you to determine all possible offspring combinations. Using the FOIL method (FIRST, OUTSIDE, INSIDE, LAST), determine the four possible combinations of alleles in the parent gametes.

5.      Place momís possible gametes across the top of the Punnett square and dadís possible gametes along the side of the Punnett square. Fill in the genotypes of the offspring in the Punnett square.

6.      Record the genotypes, the frequencies and the phenotypes of the offspring.

7.      Record the phenotypic ratio of the offspring.

8.      Repeat steps 1-7 for the ability to roll the tongue (A) and earlobes (F).

 Results:

Egg #1: dark blue, red, light green, orange

Egg #2: light blue, maroon, light green, yellow

Sperm #1: dark blue, maroon, light green, yellow

Sperm #2: light blue, red, dark green, yellow

 

Dihybrid Cross #1: Presence of Absence of Dimples and Freckles

1.      What is the genotype of the mother?

 

2.      What is the phenotype of the mother?

 

 

3.      What is the genotype of the father?

 

 

4.      What is the phenotype of the father?

 

 

5.      What are the four possible gametes produced by the mother? (use the FOIL method to determine this)

 

6.      What are the four possible gametes produced by the father?

 

 

7.      Complete the Punnett square to determine the genotypic and phenotypic ratios of the offspring.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Genotypes                               Frequencies                             Phenotypes

 

 

 

 

 

 

 

Phenotypic ratio: _________________________________________________________

 

Dihybrid Cross #2: Tongue Rolling and Earlobes

8.      What is the genotype of the mother?

 

 

9.      What is the phenotype of the mother?

 

 

10.  What is the genotype of the father?

 

 

11.  What is the phenotype of the father?

 

 

12.  What are the four possible gametes produced by the mother? (use the FOIL method to determine this)

 

13.  What are the four possible gametes produced by the father?

 

 

14.  Complete the Punnett square to determine the genotypic and phenotypic ratios of the offspring.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Genotypes                               Frequencies                             Phenotypes

 

 

 

 

 

 

 

Phenotypic ratio: _________________________________________________________