A number of different color variants have been developed for one of the species

Question

A number of different color variants have been developed for one of the species of a landscape ornamental. All of these variants are true breeding, meaning homozygous for their particular characteristic. Below are results of two crosses between a few parental strains. Based on these results develop a hypothesis that most easily explains these results. Assign genotypes to the parents, F1 and F2. (Hint: think two-gene interactions for cross #2, and use a branch diagram for sorting out phenotypes.)

Mating

Parents

F1 phenotypes

F2 phenotypes

1

red X blue

all red

102 red, 33 blue

2

red X white

all red

133 red, 58 white, 43 blue

Mating

Parents

F1 phenotypes

F2 phenotypes

1

red X blue

all red

102 red, 33 blue

2

red X white

all red

133 red, 58 white, 43 blue

Explanation / Answer

Cross 1:

Parents : red x blue

                (RR)     (bb)

F1 Offsprings: Rb, Rb,

The genotypes Rb, Rb indicate all red phenotypes.

F2 offsprings : The genotypes Rb, bb indicate 3 red and 1 blue phenotypes. Thus the offspring are produced in 3:1 ratio (monohybrid cross ratio).

Cross 2: red x white

RR   x Wb

F1 offspring : RW and Rb - all are red phenotype.

F2 offspring : RW, Rb and Wb - 1:2:1

! - white, 2 red and 1 blue phenotypes are obtained because of the independent assortment and incomplete dominance.

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