Solutions For An Introduction to Genetic Analysis Chapter 6 Problem 75P

b. Let us assume that orange and yellow are alleles of gene A with orange as the dominant color.

Cross 1

Parent

A/A X a/a

F₁

A/a

F₂

3 A/-

1 a/a

Cross 2

Assume that red is dominant over orange, which is again dominant over yellow and let the alleles be

Red A^R

Orange A^O

Yellow A^Y

Crosses 1-3 becomes

A ^O /A ^O X A^Y/A^Y A^R/A^R X A^O/A^O A^R/A^R X A^Y/A^Y

F₁

A ^O /A ^Y A ^R /A ^O A ^R /A ^Y

F₂

3 A^O/-: 1 A^Y/A^Y 3A^R/-: 1A^O/A^O 3 A^R/-:1 A^Y/A^Y

Cross 4

To perform this cross a second gene has to be added. Thus accordingly the characters of the above cross would be rewritten. If B allows color and block the expression of b then a white color would be produced.

Parent

A ^O /A ^O ; B/B X A^Y/A^Y; B/B

F₁

A ^O /A ^Y ; B/B

F₂

3 A^O/-; B/B: 1 A^Y/A^Y; B/B

Parent

A ^R /A ^R ; B/B X A^O/A^O; B/B

F₁

A ^R /A ^O ; B/B

F₂

3 A^R/-; B/B: 1 A^O/A^O; B/B

Parent

A ^R /A ^R ; B/B X A^Y/A^Y; B/B

F₁

A ^R /A ^Y ; B/B

F₂

3 A^R/-: 1 A^Y/A^Y; B/B

The fourth cross is

Parent

A ^R /A ^R ; B/B X A^R/A^R; b/b

F₁

A ^R /A ^R ; B/b

F₂

3 A^R/A^R; B/-: 1 A^R/A^R; b/b

Cross 5

Note that there is no orange appearing. Hence, two parents should carry the alleles for red and yellow and the expression of red would be blocked

Parent

A ^Y /A ^Y ; B/B X A^R/A^R; b/b

F₁

A ^R /A ^Y ; B/b

F₂

9 A^R/-; B/- red

3 A^R/-; b/b white

3 A^Y/A^Y; B/- yellow

1 A^Y/A^Y; b/b white

Cross 6

Parent

A ^O /A ^O ; B/B X A^R/A^R; b/b

F₁

A ^R /A ^O ; B/b

F₂

9 A^R/-; B/- red

3 A^R/-; b/b white

3 A^O/A^O; B/- orange

1 A^O/A^O; b/b white

Cross 7

Yellow is suppressed by b/b

Parent

A ^R /A ^R ; B/B X A^Y/A^Y; b/b

F₁

A ^R /A ^Y ; B/b

F₂

9 A^R/-; B/- red

3 A^R/-; b/b white

3 A^Y/A^Y; B/- yellow

1 A^Y/A^Y; b/b white