as the title suggest, i am confused when i read about "testcross" and linkage
Genetic linkage means that two genes segregate together, which means that they are close together on the same chromosome.
The measure of linkage is the frequency at which two genes become seperated during recombination, when they are further apart it is more likely that they become seperated.
Just to expand on what has already been said.
If genes are linked then they act as if they are on the same chromosome. That is to say whenever gene A is observed so is gene B. However, for non-sex chromosomes, each person has 2 of the "same" autosome, one from the maternal line and the other from the paternal line. There is a chance that recombination will take place between these the paternal and maternal autosome thereby making a hybrid paternal and maternal chromsome. If the genes are physically far apart on the chromsome there is a higher frequency that they will undergo recombination (the shuffling stuff that makes the hybrid chromosome.) If the genes are physically really close, then there is a lower frequency of recombination.
By physically I mean literally mean physically, i.e. number of base pairs apart.
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