This is a second part to the previous question (same cross). Again, you have a t

Question

This is a second part to the previous question (same cross). Again, you have a two-gene cross. Assume we are working with pea plants that have the following phenotypes: Plant 1: Dwarf plant and round peas (dwarf is recessive, round is dominant). This plant is the offspring of parent plants with one parent being tall with wrinkled peas and the other parent tall with round peas (think about the genotype that makes plant 1). Plant 2: Tall plant and round peas. This plant is the offspring of a true-breeding tall, round pea plant and a true breeding dwarf, wrinkled pea plant. What is the probability of obtaining plants that have a phenotype of tall and wrinkled? Enter your answer as a percentage out of 100. For instance, if your calculated answer is 0.10, enter 10. Round to the nearest whole number and do not use a percentage sign.

Explanation / Answer

Let the alleles for height is T (tall, dominant) and t (dwarf, recessive)

Alleles for seeds is R (round, dominant) and r (wrinkled, recessive)

About Plant 1, Phenotype is Dwarf and Round

Parents of plant 1 are tall with wrinkled peas and the other parent tall with round peas

Parent 1 could have genotype TTrr or Ttrr

Parent 2 could have genotype TTRR or TtRr

Because, plant 1 is dwarf it means both parents are heterozygous for height i.e. Tt

As parent 1 has wrinkled seeds (rr) and parent 2 has round seeds, plant 1 has to be heterozygous (Rr) for seeds whether parent 2 has genoptype RR or Rr for seed.

Genotype of plant 1 is ttRr,

Gametes will be tR , tr

About plant 2, Tall plant and round peas

Parent 1 is true-breeding tall, round pea plant so genotype is TTRR

Parent 2 is true breeding dwarf, wrinkled pea plant so genotype is ttrr

Genotype of plant 2 is TtRr

Gametes TR, Tr, tR, tr

Cross of plant 1 and plant 2

TtRR

Tall with round seeds

TtRr

Tall with round seeds

ttRR

Dwarf with round seeds

ttRr

Dwarf with round seeds

TtRr

Tall with round seeds

Ttrr

Tall with wrinkled seeds

ttRr

Dwarf with round seeds

ttrr

Dwarf with wrinkled seeds

Total phenotypes are Tall with round seeds, Tall with wrinkled seeds, Dwarf with round seeds, Dwarf with wrinkled seeds in ratio of 3: 1: 3:1

Required phenotype is Tall with wrinkled seeds

Probability of Tall with wrinkled seeds = 1/8 = 12.5% or 13 (Rounded value)

TR Tr tR tr tR

TtRR

Tall with round seeds

TtRr

Tall with round seeds

ttRR

Dwarf with round seeds

ttRr

Dwarf with round seeds

tr

TtRr

Tall with round seeds

Ttrr

Tall with wrinkled seeds

ttRr

Dwarf with round seeds

ttrr

Dwarf with wrinkled seeds

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