The farther apart the genes are,
the more they act like they're unlinked
This principle works for people too -- the farther apart you are, the less linked you feel. Best
friends hold hands or poke each other or whatever. On the other hand, when you were 15 and your
mother wouldn't let you get your eyebrow pierced, you walked a half a block behind her, right?
Back to genes, the ultimate in being far apart is to be on different chromosomes. Then the genes assort independently. But, two genes can be really far apart on the same chromosome, and they get split apart so often by chance that they assort almost independently. Or, they can be so close together that they almost never separate.
Keep thinking about the double hybrid cross ET/et x ET/et:
- If the genes are completely linked (no crossover), then we can only get the phenotypes
and
for offspring, in a 3:1 ratio. - If the genes were to assort separately, we would get all 4 phenotypes in the familiar 9:3:3:1 ratio.
So look what happens when we allow the crossover rate to increase or decrease:
Phenotypes ratios and crossover rate
Click the buttons to increase or decrease the cross-over rates.
0%
Proportions of offspring from ET/et x ET/et cross:
...
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