Name:_____________________________________  Period:__________

Monohybrid 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. HINT: (Suppose mom has one dark blue and one light blue piece of yarn. Dark blue represent dimples (D) and the light blue represents no dimples (d). Momís genotype would be Dd and her phenotype would be dimples.)

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

4.      Since it is random which sperm will fertilize each egg, a Punnett square will allow you to determine all possible offspring combinations. 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.

5.      Record the genotypic and phenotypic ratios of the offspring.

6.      Repeat steps 1-6 for the other traits (colors).

 Results:

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

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

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

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

Trait #1: Presence of Absence of Dimples

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

 

 

 

 

 

 

 

 

 

Genotypic ratio: _________________________________________________________

 

Phenotypic ratio: _________________________________________________________

Trait #2: Presence of Absence of Freckles

6.      What is the genotype of the mother?

 

 

7.      What is the phenotype of the mother?

 

 

8.      What is the genotype of the father?

 

 

9.      What is the phenotype of the father?

 

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

 

 

 

 

 

 

 

 

 

 

Genotypic ratio: _________________________________________________________

 

Phenotypic ratio: _________________________________________________________

 

Trait #3: Ability to roll tongue

11.  What is the genotype of the mother?

 

12.  What is the phenotype of the mother?

 

 

13.  What is the genotype of the father?

 

 

14.  What is the phenotype of the father?

 

 

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

 

 

 

 

 

 

 

 

 

Genotypic ratio: _________________________________________________________

 

Phenotypic ratio: _________________________________________________________

 

Trait #4: Free or attached earlobes

16.  What is the genotype of the mother?

 

 

17.  What is the phenotype of the mother?

 

 

18.  What is the genotype of the father?

 

 

19.  What is the phenotype of the father?

 

 

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

 

 

 

 

 

 

 

 

 

 

Genotypic ratio: _________________________________________________________

 

Phenotypic ratio: _________________________________________________________