Section: Biological and Biochemical Foundations of Living Systems

12)

	TL	Tl	tL	tl
TL	TTLL	TTlL	TtLL	TtLl
Tl	TTLl	TTll	TtLl	Ttll
tL	TtLL	TtLl	ttLL	ttLl
tl	TtLl	Ttll	ttLl	ttll

For a particular plant, straight leaves result from a dominant gene (L) and wrinkled leaves result from a recessive gene (l), and tall height results from a dominant gene (T) while short height results from a recessive gene (t). A dihybrid cross is performed with plants heterozygous for both traits. What is the expected ratio of short, straight-leaved plants to tall, straight-leaved plants?

1. 1:1
2. 1:2
3. 1:3
4. 3:1

In a dihybrid cross, the genes for two traits are crossed in a punnett square. For two heterozygotes crossed in a punnett square, the expected ratio of recessive/recessive, dominant/recessive, recessive/dominant, to dominant is 1:3:3:9. In this particular question, the ratio of both recessive/dominant to dominant/dominant is 1:3.