Question

Linkage: Consider three genes, each with two alleles. An individual with genotype AAbbDD is crossed with an individual whose genotype is aaBBdd. What are all the gamete types (gamete genotypes) that their offspring (AaBbDd) can produce? Draw chromosome diagrams if it helps you to answer the question.

a. If the three genes are unlinked?

b. If all three links are tightly linked (no crossing over)?

c. If the first two genes are tightly linked (no crossing over), but the third gene is on a different chromosome pair?

Answer 1

Answer:

a).

AAbbDD x aaBBdd –Parents

AaBbDd ------------F1

If genes are unlinked, AaBbDd genotype produces 8 types of gametes as bellow:

1. ABC

2. ABc

3. AbC

4. Abc

5. aBC

6. aBc

7. abC

8. abc

b).

AbD/AbD x aBd/aBd –Parents

AbD/aBd------- ------------F1

If genes are unlinked, AbD/aBd genotype produces only two types of gametes as bellow:

1. AbD

2. aBd

c).

Ab/Ab; DD x aB/aB; dd –Parents

Ab/aB; Dd------- ------------F1

If first two genes are linked & third gene is not linked, Ab/aB; Dd genotype produces 8 types of gametes as bellow.

1. AB; D

2. AB; d

3. Ab; D

4. Ab; d

5. aB; D

6. aB; d

7. ab; D

8. ab; d