F2
Repulsion Progeny Part I
AaBb x AaBb F2
progeny
One should expect 9:3:3:1 ratio w/o linkage
With repulsion linkage we expect:
| class
of gametes |
expected
proportion |
| AB |
p |
| Ab |
1-p |
| aB |
1-p |
| ab |
p |
We can derive the expected proportions of each of the
classes of zygotes using a Punnett square. We use the
concept of independence for the probability of male
and female gametes uniting. We are not assuming independence
between the A and B loci.
| |
P/2
AB |
(1-p)/2
Ab |
(1-p)/2
aB |
p/2
ab |
| p/2AB |
AABB
p2/4 |
p(1-p)/4 |
p(1-p)/4 |
p2/4 |
| (1-p)/2Ab |
p(1-p)/4 |
(1-p)2/4 |
(1-p)2/4 |
p(1-p)/4 |
| (1-p)/2aB |
p(1-p)/4 |
(1-p)2/4 |
(1-p)2/4 |
p(1-p)/4 |
| p/2
ab |
p2/4 |
p(1-p)/4 |
p(1-p)/4 |
p2/4
aabb |
Let us collect like terms.
| class |
Proportion |
A_B_
Phenotype |
| AABB |
p2/4 |
| AABb |
p(1-p)/4 |
| AaBB |
p(1-p)/4 |
| AaBb |
p2/4 |
| AABb |
p(1-p)/4 |
| AaBb |
(1-p)2/4 |
| AaBB |
p(1-p)/4 |
| AaBb |
p(1-p)2/4 |
| AaBb |
p2/4 |
p2
+ p2
+ p2
+ p(1-p) + p(1-p)
+ p(1-p) + p(1-p)
4 4 4 4 4 4 4
+ (1-p)2
+ (1-p)2
4 4
= 3p2
+ 4p(1-p) + 2(1-p)2
4 4 4
= 3p2 + 4p
- 4p2
+ 2(1 - 2p + p2)
4
= 3p2
+ 4p - 4p2 + 2 - 4p
+ 2p2
4
= p2
+ 2
4
= P(A_B_)
