Lecture 19 - Linkage, recombination and mapping Flashcards
what are genetic maps?
> genetic mapping is a part of genetic analysis used to determine the location and relative order of genes on a chromosome,
it relies on two important concepts in genetic analysis:
genetic linkage and genetic recmbination
what happens in recombination?
if recombination happens, 4 gametes are produced. 2 are identical to the parental chromosomes and 2 are recombinants. recombinants are less frequent than parental types.
who developed the theory of chromosomal inheritance?
Thomas hunt Morgan using drosophila.
describe and explain drosophila genetic
> Traditionally used mutagenesis, mutate gene, see what happens
test crosses for linkage were used
what is the expected ratio of offspring if independently assorting?
> 4 unique gametes
> 4 unique types of offspring
what happens in a test cross if complete linkage?
2 unique gametes from F1
2 types of offspring identical to the parents
what is the expected ratio of offspring in a test cross if incomplete linkage?
parental phenotypes are more common than the recombinants.
what happens in linkage in autosomes?
> genes on the same chromosome tend to co-segregate
linkage breaks the law of independent assortment
linkage is rarely complete.
because of the exchange of segments during cross over.
explain the fundamentals of gene mapping
> genes along a chromosome are “linked” - referred to as linkage group
recombination breaks the original linkage of alleles - parental genotype (the original configuration) - recombinant phenotype (the new configuration)
recombination is proportional to distance
- tightly linked genes (more linkage) = less recombination
- weakly linked genes (less linkage) = more recombination
- unlinked genes (no linkage) = recombinant frequency = parental frequency, independent assortment.
how do you calculate the recombination frequency?
no. recombinants/ total offspring
how do you calculate the distance between genes?
% recombination = no. map units (centiMorgan or cM)
what is the maximum apparent recombination frequency?
50%
> this is the same as independent assortment of genes on different chromosomes.
