Question

Recall that mendel crossed a true breeding tall, purple-flowered pea plants with a true breeding dwarf, white flowered plant. All the f1 plants were tall and purple flowered. If an f1 plant is now self-pollinated, what is the probability of obtaining an f2 plant heterozygous for the genes controlling height and flower color?

Answer 1

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Answer on Question #64124 - Biology - Genetics

Recall that mendel crossed a true breeding tall, purple-flowered pea plants with a true breeding dwarf, white flowered plant. All the f1 plants were tall and purple flowered. If an f1 plant is now self-pollinated, what is the probability of obtaining an f2 plant heterozygous for the genes controlling height and flower color?

Solution

Alleles:

- T – tall allele

- t – dwarf allele

- P – purple-flowered allele

- p – white flowered allele

All parental plants are true breeding, so all of them are homozygous.

Genotypes of parental plants:

- TTPP – genotypes of tall, purple-flowered pea plant (homozygous dominant)

- ttpp – genotype of dwarf, white flowered plant (homozygous recessive)

Gametes produced by parental plants:

- ttpp → tp

- TTPP → TP

Combine these gametes in the Punnet square for TTPP × ttpp crossing:

We’ve obtained all f1 plants with the same genotype TtPp (heterozygote) and with the phenotype of tall and purple flowered plant.

At the next step f1 plants were crossed: TtPp × TtPp

TtPp plant can produce 4 types of gametes:

- TtPp → TP, Tp, tP, tp

So, the Punnet square:

In conclusion, from 16 offsprings (f2 generation) only 4 plants have genotype TtPp (heterozygous heterozygous for the genes controlling height and flower color)

Probability of TtPp f2 genotype: $4/16 = 1/4 = 25\%$

Answer:

the probability of obtaining an f2 plant heterozygous for the genes controlling height and flower color is $1/4$