Question

genetics practice problems

1. set up the punnett squares for each of the crosses listed below. purple flowers are dominant to white.

rr x rr
what percentage will be purple? what percentage will be white?
rr x rr
what percentage will be purple? what percentage will be white?
rr x rr
what percentage will be purple? what percentage will be white?
practice with crosses. show all work!

1. a tt (tall) plant is crossed with a tt (short plant).

what percentage of the offspring will be tall?

1. show the cross of a tt plant and a tt plant.

what percentage of the offspring will be short? what percentage is tall?

1. a heterozygous round - seeded plant (rr) is crossed with a homozygous round - seeded plant (rr).

what percentage of the offspring will be homozygous (rr)?

1. a white flowered plant is crossed with a plant that is heterozygous for the trait.

what percentage of the offspring will have purple flowers? white flowers?

1. two plants, both heterozygous for the gene that controls flower colors are crossed.

what percentage of their offspring will have purple flowers? what percentage will have white flowers?

Explanation:

Step1: Analyze Rr x rr cross

The possible gametes from Rr are R and r, and from rr are r. The Punnett - square has 4 boxes. The genotypes of the offspring are Rr:rr = 1:1. Since purple (R) is dominant over white (r), the percentage of purple flowers is 50% and white flowers is 50%.

Step2: Analyze Rr x Rr cross

The possible gametes from both Rr parents are R and r. The Punnett - square gives genotypes RR:Rr:rr = 1:2:1. The percentage of purple flowers (RR + Rr) is 75% and white flowers (rr) is 25%.

Step3: Analyze RR x Rr cross

The possible gametes from RR are R and from Rr are R and r. The genotypes of the offspring are RR:Rr = 1:1. Since all genotypes have the dominant R allele, the percentage of purple flowers is 100% and white flowers is 0%.

Step4: Analyze TT x tt cross

The possible gametes from TT are T and from tt are t. All offspring have the genotype Tt. Since tall (T) is dominant over short (t), 100% of the offspring are tall.

Step5: Analyze Tt x Tt cross

The possible gametes from both Tt parents are T and t. The genotypes are TT:Tt:tt = 1:2:1. The percentage of short plants (tt) is 25% and tall plants (TT + Tt) is 75%.

Step6: Analyze Rr x RR cross

The possible gametes from Rr are R and r, and from RR are R. The genotypes of the offspring are RR:Rr = 1:1. The percentage of homozygous (RR) offspring is 50%.

Step7: Analyze white (rr) x Rr cross

The possible gametes from rr are r and from Rr are R and r. The genotypes of the offspring are Rr:rr = 1:1. The percentage of purple flowers (Rr) is 50% and white flowers (rr) is 50%.

Step8: Analyze Rr x Rr (again for flower - color in 11)

The possible gametes from both Rr parents are R and r. The genotypes are RR:Rr:rr = 1:2:1. The percentage of purple flowers (RR + Rr) is 75% and white flowers (rr) is 25%.

Answer:

• Rr x rr: 50% purple, 50% white
• Rr x Rr: 75% purple, 25% white
• RR x Rr: 100% purple, 0% white
• TT x tt: 100% tall
• Tt x Tt: 25% short, 75% tall
• Rr x RR: 50% homozygous (RR)
• White (rr) x Rr: 50% purple, 50% white
• Rr x Rr (in 11): 75% purple, 25% white