4

Question

Monohybrid Cross - Pea Characters

Classical Genetics-Laboratory Exercise 4 Set up Punnet squares for each of the crosses listed below. Show you work. Always show the genotype

and phenotype of the offspring and its ratios then answer the questions

A. Round seeds are dominant to wrinkled seeds

1. In a cross between Rr x m, what percentage of offspring will be round?

2. In a cross between RR x Rr, what percentage of offspring will be round?

3. In a cross between Rrx Rr, what percentage of offspring will be round?

4. A homozygous round seeded plant is crossed with a homozygous wrinkled seeded plant. What are

the genotypes of the parents? What percentage of the offspring will also be homozygous?

B. Tall plant is dominant to short plant

1. ATT plant is crossed with a tt. What percentage of the offspring will be tal?

2. A Tt plant is crossed with a Tt plant. What percentage of the offspring will be short?

3. A heterozygous tall plant is crossed with a homozygous tall plant. What percentage of the offspring

will be homozygous?

C. Purple flowers are dominant to white flowers 1. two white flowered plants are cross, what percentage of their offspring will be white flowered?

2. A white flowered plant is crossed with a plant that is heterozygous for the trait. What percentage of the

offspring will have purple flowers?

3. Two plants, both heterozygous for the gene that controls flower color are crossed. What percentage of their offspring

Answer 1

1. In a cross between Rr x m, the percentage of offspring that will be round can be calculated using a Punnett square.

Rr x m
R m
r m

In this cross, 50% of the offspring will be round.

2. In a cross between RR x Rr, the percentage of offspring that will be round can also be calculated using a Punnett square.

RR x Rr
R R
R R

In this cross, 100% of the offspring will be round.

3. In a cross between Rr x Rr, the percentage of offspring that will be round can be calculated using a Punnett square.

Rr x Rr
R r
R r

In this cross, 75% of the offspring will be round.

4. A homozygous round seeded plant (RR) is crossed with a homozygous wrinkled seeded plant (rr). The genotypes of the parents are RR and rr.

When these two parents are crossed, all of the offspring will be heterozygous (Rr) for the round seed trait. So, 0% of the offspring will be homozygous.

B. Tall plant is dominant to short plant

1. In a cross between ATT plant and tt, the percentage of offspring that will be tall can be calculated using a Punnett square.

ATT x tt
AT tt
AT tt

In this cross, 100% of the offspring will be tall.

2. In a cross between Tt plant and Tt plant, the percentage of offspring that will be short can be calculated using a Punnett square.

Tt x Tt
T t
T t

In this cross, 25% of the offspring will be short.

3. A heterozygous tall plant (Tt) is crossed with a homozygous tall plant (TT). The percentage of offspring that will be homozygous can be calculated using a Punnett square.

Tt x TT
T T
t T

In this cross, 50% of the offspring will be homozygous.

C. Purple flowers are dominant to white flowers

1. In a cross between two white flowered plants, the percentage of their offspring that will be white flowered can be calculated using a Punnett square.

ww x ww
w w
w w

In this cross, 100% of the offspring will be white flowered.

2. In a cross between a white flowered plant (ww) and a plant that is heterozygous for the trait (Ww), the percentage of the offspring that will have purple flowers can be calculated using a Punnett square.

ww x Ww
w W
w w

In this cross, 0% of the offspring will have purple flowers.

3. In a cross between two plants that are heterozygous for the gene that controls flower color (Ww x Ww), the percentage of their offspring that will have purple flowers can be calculated using a Punnett square.

Ww x Ww
W W
W w

In this cross, 75% of the offspring will have purple flowers.