Lecture 8: Genetic Linkage Flashcards
State the main characteristics of independent assortment in meiosis.
• The orientation of the maternally and paternally derived chromosomes on the metaphase plate in meiosis I is random!
• Input into meiosis II could be the same as the parental gametes or could be a mix of maternally and paternally derived chromosomes.
If we consider two genes located on different chromosomes, independent assortment predicts that 50% of gametes will be non-recombinant (gametes with both alleles in red and gametes with both alleles in blue) and 50% recombinant (gametes with one allele red and the other blue).
What are recombinant gametes?
Gametes containing a mixture of maternally and paternally derived chromosomes.
What are some ways of increasing genetic variation?
• Crossing-over (recombination), to create new combinations of alleles.
• Independent assortment.
What are genetic outcomes dependent on?
Location of genes on chromosomes.
What is the outcome of genes located on different chromosomes?
50% recombinants, 50% non-recombinants.
Why is the maximum recombination frequency 50%?
No recombination is more likely than a single crossover event, which is much more likely than a double crossover event. As no recombination is most likely, that must occur in over 50% of cases.
The remaining two strands that were not involved in the crossover generate two non-recombinant gametes.
What will happen to genes that are located in close proximity on a chromosome?
They will segregate together in most cases.
What is chiasmata?
Sites of genetic exchange.
What is a chromosome map?
Idiograms, help pinpoint the locations of genes and locate abnormal gene forms on chromosomes.
How many centiMorgans is a single map unit equal to?
1 map unit = 1% recombination between genes on the same chromosome = 1 centiMorgan (cm).
