7.2: linkage Flashcards
Under what circumstances does mendel’s 2nd law not apply?
Mendel’s second law says that the inheritance of one allele of one gene does not affect the inheritance of another allele in a different gene.
HOWEVER. This is only true when genes are on separate chromosomes. When genes are on the same chromosome there is a greater tendency for the two genes to remain together (e.g. bc they’re on the same chunk of chromosome and this whole chunk may stay together during reshuffling… so there’s a higher probability to inherit the linked alleles for different genes. together. The strength of this linkage can be measured using RCVs.
What are the three sources of genetic diversity?
The three sources of genetic diversity are…
- Independent orientation of chromosomes in meiosis
- Crossing over
- Random fertilisation of gametes
What is linkage?
Linkage describes the tendency of two genes to remain together during inheritance. This happens because they are located on the same chromosome and the effect is greater when they are closer together.
How is linkage measured?
Linkage is greater when genes are closer together on a chromosome, so strength of linkage can be measured by how close the genes are using RCVs or recombination values.
What are recombination values RCVs?
Recombination values describe the frequency of recombinant (non-parental) genotypes. In meiosis we would expect
If there is a high recombinant frequency it means there is only a small or no trend for the genes to be inherited together in any pattern. In other words, there is not much linkage.
–> 50% RCV indiciates free recombination, or high odds of recombo.
If there is a low RCV this means a large proportion of individuals inherit the parental genotype: the alleles stick together. This means there is a strong tendency towards linkage and so therefore they must be closer together.
–> 0% means absolute linkage: so close there is absolutely no chance of crossover between them.
Why can’t you have an RCV of 100%?
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What is coupling and repulsion?
Coupling is the tendency to inherit both dominant alleles from the same parent.
Repulsion is the tendency to inherit dominant alleles from different parents.
