INTRODUCTION – For the crosses in this activity, we will use some of the traits that Mendel observed in garden peas. Remember, the genotype of each plant must have two letters, one representing each allele of the gene for that particular trait. For example, if R stands for round seeds and r stands for wrinkled seeds. Then a round seed could have two different genotypes (RR or Rr.) The R is dominant to r. Therefore, the only way a seed could be wrinkled is to have the genotype rr. These three situations have names. RR is called homozygous dominant because the two alleles are the same (homo) and dominant. Rr is called heterozygous because the two alleles are different (hetero.) Lastly, rr is called homozygous recessive, because the alleles are the same, but they are masked by the stronger round gene.

DIRECTIONS – In the problems that follow, we will predict the offsprings phenotype, or what the offspring will look like. Use the information and symbols from the chart below.

PROBLEMS – Using a Punnet square, predict the genotypic ratio and phenotypic ratio for the following crosses. Always write down the genotype of the parents if it is not supplied for you.

1. RR X rr Genotypic ratio ___________________ Phenotypic ratio_______________

2. GG X Gg Genotypic ratio ___________________ Phenotypic ratio_______________

3. TT X Tt Genotypic ratio ___________________ Phenotypic ratio_______________

4. Tt X Tt Genotypic ratio ___________________ Phenotypic ratio_______________

5. Rr X Rr Genotypic ratio ___________________ Phenotypic ratio_______________

6. BB X Bb Genotypic ratio ___________________ Phenotypic ratio_______________

7. Cross two homozygous green plants. Genotypic ratio _________________Phenotypic ratio_______________

8. Cross a homozygous green plant with a heterozygous green plant

Genotypic ratio _________________Phenotypic ratio_______________

 

 

 

 

9. cross a white seed plant with a heterozygous brown seed plant

Genotypic ratio _________________Phenotypic ratio_______________

 

 

 

 

10. Cross two plants that are heterozygous for brown seed coats

Genotypic ratio _________________Phenotypic ratio_______________

 

 

 

 

11. Cross a tall plant with a short plant. Show all of the possibilities.

12. Cross a plant with green pods with a plant with yellow pods. Show all of the possibilities.