Question

In peas the flower color and pollen length genes are very close together on the same chromosome. Purple flowers (P are dominant to white (p), and long pollen (L) is dominant to short pollen (l). A true breeding variety of peas with purple flowers and short pollen is crossed to a true breeding variety with white flowers and long pollen. The F1 plants are then self-crossed to produce an F2 generation. a. What is the genotype and phenotype of the F1 generation? b. What proportion of the F2 will have purple flowers with long pollen? c. What proportion will have white flowers and short pollen?

Answer 1

a. Genotype: PpLl, Phenotype: Purple flower, long pollen

b. 9/16

c. 1/16

Step-by-step explanation:

This question involves two distinct genes; one coding for flower colour and the other for pollen length. The allele for purple color (P) is dominant over the allele for white color (p) in the first gene while the allele for long pollen (L) is dominant over the allele for short pollen (l) in the second gene.

A truebreeding plant is an homozygous plant i.e. it contains same alleles for a particular trait. A cross between a truebreeding pea with purple flowers and short pollen (PPll) and true breeding variety with white flowers and long pollen (ppLL) will produce an all heterozygous F1 offsprings with genotype: PpLl.

If this offsprings are self-crossed i.e. PpLl × PpLl, each parent will produce gametes via meiosis in the following possible allelic combination:

PpLl- PL, Pl, pL and pl

Using these gametes in a punnet square (see attached image), 16 possible offsprings will be produced in the ratio 9:3:3:1.

9/16 of the offsprings will be dominant for both traits (genes) i.e. PPLL, PpLl, PPLl or PpLL

3/16 will be dominant for first gene and recessive for the second i.e. PPll or Ppll

3/16 will be dominant for the second trait (gene) and recessive for the first i.e. ppLL or ppLl

1/16 will be recessive for both genes (traits) i.e. ppll