Topic 3: Gametic Disequilibrium/Linkage Disequilibrium

Question 1

mendel’s laws (2)

Answer 1

first law: random segregation
- alleles at a single locus segregate randomly, offspring have a 50% chance of inheriting each of a parent’s alleles (basis of HW)

second law: independent segregation/assortment
- alleles at diff loci segregate independently, so that inheritance of alleles at locus A is independent of alleles at locus B

Question 2

mendel’s second law: independent segregation/assortment:
when is this true? when is this not true?

Answer 2

true when loci are located on diff chromosomes, but if they are located close together on same chromosome, they will not always segregate independently, and can be inherited as a single “unit”

these loci are said to be LINKED, will result in linkage disequil or gametic disequil

Question 3

another name for gametic disequil?

Answer 3

nonrandom genotype associations

Question 4

can you have perfect HW equil with gametic disequil?

Answer 4

Yeah!
ex. 25 AABB, 50 AaBb, 25 aabb
perfect gametic equil would have:
ex. AABB, AaBb, aabb, AABb, AaBB, aaBb, aaBB, AAbb, Aabb

Question 5

def of gametic disequil?

Answer 5

nonrandom genotype (and hence allelic) associations among loci (aka linkage disequil)

Question 6

other than linkage disequil, what does gametic disequil include?

Answer 6

selection, genetic drift, migration

Question 7

meiosis meaning

Answer 7

four haploid gametes produced from a diploid parent cell (located in gonads)

Question 8

recombination meaning?

Answer 8

process by which sister chromosomes can exchange pieces of DNA during meiosis by crossing over

Question 9

what breaks down gametic disequil?

Answer 9

recombination!
AB + ab = AaBb (coupling phase double het)
Ab + aB = AaBb (repulsion phase double het)

Question 10

when r = 0.5, can there still be gametic disequil?

Answer 10

There cannot be linkage disequil, but there CAN be gametic disequil (e.g., drift, selection, migration)

Question 11

when we consider gametic disequilibrium, do we use multilocus genotype freq or gamete freq?

Answer 11

gamete freq bc it’s easier

Question 12

what are the 2 ways that gametes can unite to form a double heterozygote?

Answer 12

AB + ab = AaBb (coupling)
Ab + aB = AaBb (repulsion)

Question 13

only recombination in individuals that are ______ at both loci will change gamete frequencies over time (and approach 0 for gametic disequil)

Answer 13

heterozygous

Question 14

recombination in coupling phase double heterozygotes creates?

Answer 14

Ab and aB repulsion phase gametes

Question 15

How are gametic disequil and sexual reproduction connected? (their relationship) (3)

Answer 15

1. matings between diff individuals result in new combinations of genes in offspring
2. recombination and crossing over in meiosis during gametogenesis creates genetic diversity
3. recombination and crossing over in meiosis breaks down gametic disequil, which will also increase genetic diversity

these factors increases genetic diverse offspring, allow purging of deleterious mutations

Question 16

in conjunction with HW disequil, gametic disequil can provide additional evidence for _______ _____ or _____ _____

Answer 16

asexual reproduction
or
cryptic species

Question 17

why do we want to test for gametic disequil when analyzing diploid pop genetic data?

Answer 17

we want each locus to provide us with an INDEPENDENT ASSESSMENT of questions of interest
- e.g., amount of gene flow among pops, amount of genetic differentiation among pops, forensic analyses