Punnett Square Homework for CST Review

Directions: Punnett squares are tools that are used to predict the traits of offspring when mating is involved. Punnett squares reveal the probable phenotype (physical appearance) and genotype (DNA codes) of the offspring. Answer the following questions using your notes, textbook, or internet.

Example: Cross two heterozygous (Bb) blue pea plants. Punnett Square BABY STEPS: The recessive color is white. B b 1. determine the genotypes of the parent B BB Bb organisms 2. write down your "cross" (mating) b Bb bb 3. draw a p-square 4. "split" the letters of the genotype for each Genotype: 25% BB, 50% Bb, 25% bb parent & put them "outside" the p-square Phenotype: 75% Blue, 25% white 5. determine the possible genotypes of the offspring by filling in the p-square Homozygous: Same alleles 6. summarize results (genotypes & from parents. Ex: AA or aa phenotypes of offspring) Heterozygous: Different alleles 7. bask in the glow of your accomplishment from parents. Ex: Aa

1. In pea plants, yellow (Y) plants are dominant over green (y) plants. Complete the following crosses and give the genotypic and phenotypic ratios of offspring. a. YY x yy

Genotype: ______

Phenotype: ______b. Yy x yy

Genotype: ______

Phenotype: ______c. Yy x Yy

Genotype: ______

Phenotype: ______

2) In pea plants, blue flowers (B) are dominant over white (b) flowers. Complete the following crosses and give the genotypic and phenotypic ratios of offspring. a. A heterozygous blue plant is crossed with a homozygous white plant.

Genotype: ______

Phenotype: ______

b. A cross between two pea plants produces offspring in which approximately 50% of the flowers are white and 50% are blue. What are the genotypes of the parents? Show the Punnett square to support your answer.

3) One cat carries heterozygous, long-haired traits (Ss), and its mate carries homozygous short-haired traits (ss). Use a Punnett square to determine the probability of one of their offspring having long hair.

4) One cat carries heterozygous, long-haired traits (Ss), and its mate carries homozygous short-haired traits (ss). Use a Punnett square to determine the probability of one of their offspring having short hair.

5) One flower is heterozygous red (Rr) and it is crossed with a homozygous white (rr) plant. Use a Punnett square to determine the probability of one of their offspring having a white color.

6) In a certain species of plant, the color purple (P) is dominant to the color white (p). According to the Punnett Square, what is the probability of an offspring being white?

7) In a certain species of plant, the color purple (P) is dominant to the color white (p). According to the Punnett Square, what is the probability of an offspring being purple?