Genetics Exam 2 topic 5

Linkage and mapping

What phenomenon causes traits to violate Mendel’s principle of independent assortment

Linkage!

Why are two genes in close proximity sometimes inherited together?

Because crossing over didn’t happen

Does linkage result in more parental or recombinant chromosomes

More parental chromosomes

how is linkage measureable?

as the percent recombination which is also used as a measure of genetic distance

If crossing over happens between the two genes in every meiosis what percentage of gametes are recombinant?

50%

What test can we run to tell if genes are linked

a test cross (heterozygous parent with homozygous recessive parent)

If the dominant alleles are on opposite chromosomes is this coupling or repulsion?

They are in repulsion

If the dominant alleles are the same chromosome is this coupling or repulsion?

coupling

How is repulsion noted?

Ab||aB or Ab|aB or Ab/aB

How is coupling noted?

AB||ab or AB|ab or AB/ab

What is the definition of coupling?

Dominant alleles stay together in parental

What is the definition of repulsion?

Dominant alleles stay apart in Parental

Recombination Frequency equation?

Recombinants(aka non parental genotypes)/total offspring x 100

What are the units that recombination frequency (RF) is equivalent to?

0.01 (RF) = 1 centiMorgan (cM) = 1 map unit (m.u.)

what is the maximum distance a test cross can measure

50cM (becuase thats 50% RF meaning crossing over always occuring!)

What is the RF for two genes on different chromosomes

50% because of independent assortment!

How does a linkage map differ from a linkage group?

a linkage map has the relative distances between each gene in the linkage group

is genetic map distance equivalent to physical distance?

Nope just how linked different genes are

Are recombination rates species specific?

yas, but they vary within a species as well

what is interference

If a single crossover event will affect the likelihood of another event nearby

How do we figure out which gene is in the middle?

Whatever gene is switching between the double crossover and the parental gametes

What is the equation for interference?

1 - (observed double recombinants/Expected double recombinants)

How to calculate the expected number of double recombinants

total number x (RF gene a-b * RF2 gene b-c)

What is the name of the graph used to interpret Genome Wide association study results?

A manhattan plot