Question

A dark-red strain and a white strain of wheat are crossed and produce an intermediate, medium-red F1. When the F1 plants are interbred, an F2 generation is produced in a ratio of 1 dark-red : 4 medium-dark-red : 6 medium-red : 4 light-red : 1 white Further crosses reveal that the dark-red and white F2 plants are true breeding.

a. Based on the ratios in the F2 population, how many genes are involved in the production of color?
b. How many additive alleles are needed to produce each possible phenotype?
c. Assign symbols to these alleles and list possible genotypes that give rise to the medium red and light red phenotypes.
d. Predict the outcome of the F1 and F2 generations in a cross between a true-breeding medium red plant and a white plant.

Answer 1

a). 2 genes are involved in production of colour in F2 generation.

b). 2 possible alleles for each phenotype

c).Rr (medium red), rr light red

d) F1 generation  1:2:1 ( 1 light red stain, 2 medium red) and F2 generation 1:1

1 medium red and 1 light red.

Explanation:

F1 generation:

dark red strain X white strain

RR X rr

  r    r

R rR  Rr

R  rR Rr

genotype ratio 4:1, all medium red

Cross between F1 generation of true breeding plants

  R  r

R RR Rr

r  Rr  rr     1 light red stain, 2 medium red, 1 white genotype ratio 1:2:1

In F2 Generation, F1 plants interbred ie true breeding

F2 generation:

    R r

r   Rr  rr

r  Rr   rr  

It produces 1 medium red and 1 light red plant. genotype ratio 1:1

Here alleles Rr is for medium red and rr is for light red

Additive allele depends on the allele concentration for a phenotype trait to appear.