Lecture 5 Flashcards
Genetic crossover
The chance of cross over is equal.
But because different distances, the chances of two genes or three gene cross over are different.
Say a and c ….. And A and C
If there is only two cross overs, they look like normal, therefore they are going to look like they are independent.
There are 50:50 of looking like that, as even:odd
But adding a third will resolve this
So the way independent occurs only if the two genes are very far apart or indendent
But screw all of this complicated stuff
RF= R/ total x100 this is the genetic distance, aka centemorial distance, recombination frequency, reflecting the physical distance, but not perfect, roughly correct.
Why? Because chances of recombination are different, because different organism cross at different rates.
How do we create a system where we can see the genotype from the phenotype.
I want to look at the genotype of the sperm but I can’t do that.
P1 AaBbx AaBb will lead to a 9:3:3:1….not useful
AaBb will lead to Ab, AB, aB, ab
By controlling the female gametes to be homozygous recessive
aabb. We can control the progeny.
The fertilization will result in genotypes that reflect the amount of each gamete. This type of cross is called a test cross.
This is based upon that the genes are located on different chromosomes. If the genes on linked together, the chances of certain games are no longer 25:25:25:25, and through this test cross, we can see p:r that are not 50:50.
