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

If the genes are closely linked to each other on a chromosome, recombination cannot occur between these genes.

the genotype of the peas with purple flowers and short pollen is PPll and genotype of true breeding variety with white flowers and long pollen is ppLL.

PPll * ppLL

Pl/pL (F1, all F1 plants have purple flowers and long pollen)

a) genotype of F1 is PpLl and phenotype of F1 is purple flowers and long pollen.

b) Pl/pL * Pl/pL

Pl/pL P and l allele is one chromosome and p and L alleles are on its homologous pair since these genes are closely linked to each other, Pl/pL can produce only two types of gametes Pl and pL.

	Pl	pL
Pl	PPll ( purple flowers and short pollen)	PpLl ( purple flowers and long pollen)
pL	PpLl ( purple flowers and long pollen)	ppLL ( white flowers and long pollen)

proportion of the F2 will have purple flowers with long pollen = number of plants with purple flowers and long pollen/total number of progeny=2/4=1/2

c)  proportion will have white flowers and short pollen= number of plants with white flowers and short pollen/total number=0/4=0.