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1. 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?
What is will the punnet square look like?

2. In pea plants purple flowers are dominant to white flowers. If two white flowered plants are crossed, what percentage of their offspring will be white flowered?
What will the punnet square look like?

3. A white flowered plant is crossed with a plant that is heterozygous for the trait. What percentage of the offspring will have purple flowers? Two plants, both heterozygous for the gene that controls flower color are crossed. What percentage if their offspring will have purple flowers? What percentage will have white flowers?
What will the punnet square look like?

1 answer

1. Round vs. Wrinkled Seeds in Pea Plants

Genotypes of the Parents:

  • Homozygous round-seeded plant: RR
  • Homozygous wrinkled-seeded plant: rr

Percentage of the Offspring that will be Homozygous: All offspring from this cross will be heterozygous (Rr). Therefore, 0% of the offspring will be homozygous.

Punnett Square:

| | R | R | |---|---|---| | r | Rr | Rr | | r | Rr | Rr |

2. Crossing Two White Flowered Plants

Genotypes of the Parents: Since white flowers are recessive, both plants must be homozygous for the white trait, so ww x ww.

Percentage of the Offspring that will be White Flowered: All offspring will inherit the ww genotype, so 100% of their offspring will be white flowered.

Punnett Square:

| | w | w | |---|---|---| | w | ww | ww | | w | ww | ww |

3. White Flowered Plant with Heterozygous Plant

Crossing a White Flowered Plant with a Heterozygous Plant:

Genotypes:

  • White flowered plant: ww
  • Heterozygous plant: Ww

Percentage of the Offspring that will have Purple Flowers: In this cross, the genotypes will be:

  • 50% will be Ww (purple).
  • 50% will be ww (white). Thus, 50% of the offspring will have purple flowers.

Punnett Square:

| | W | w | |---|---|---| | w | Ww | ww | | w | Ww | ww |

Crossing Two Heterozygous Plants:

Genotypes:

  • Both plants: Ww

Percentage of the Offspring that will have Purple Flowers: From this cross, the possible offspring genotypes will be:

  • 25% WW (purple)
  • 50% Ww (purple)
  • 25% ww (white)

Thus, 75% of the offspring will have purple flowers, and 25% will have white flowers.

Punnett Square:

| | W | w | |---|---|---| | W | WW | Ww | | w | Ww | ww |

Summary:

  1. RR x rr → 0% homozygous offspring
  2. ww x ww → 100% white flowered offspring
  3. ww x Ww → 50% purple; Ww x Ww → 75% purple, 25% white