|
|
Part II
| gametes |
proportion
expected when one crossover occurs |
| PT |
(1-r)
2 |
| pt |
(1-r)
2 |
| Pt |
r
2 |
| pT |
r
2 |
| Total |
1-r+r
+ 1-r+r
2 2 |
| |
1
+ 1 = 1
2 2 |
A crossover does not occur at each meiotic event, unless
the loci are located 50 recombination units or more
apart. When an average of one crossover occurs for each
meiotic event we have r = 1/2. We can substitute r =
1/2 for independent assortment to get the gametic ratio
of:
1/4 PT:1/4pt:1/4Pt:1/4pT
| |
One
crossover event |
| gametes |
Proportions |
r
= 1
r = 2 |
| PT |
1-r
2 |
1-
1/2 = 1
2 4 |
| pt |
1-r
2 |
1-1/2
=1
2 4 |
| Pt |
r
2 |
1/2(1/2)
=1/4 |
| pt |
r
2 |
1/2(1/2)
=1/4 |
The results demonstrate that when there is 50% recombination between
loci we achieve the gametic proportions of indepenent assortment.
Copyright
2000©, Ted Helms
|
|
