Topic 9 Population subdivision and gene flow

Question 1

Metapopulation

Answer 1

• a large population composed of 2 or more partially/completely isolated subpopulations
• mating within the metapopulation is NOT random

Question 2

subpopulation (or deme)

Answer 2

-groups of indiv. that mate randomly with each other (in absence of inbreeding and assortative mating)

Question 3

Population subdivision

Answer 3

-refers to the fact you almost never have a single panmictic population but rather subpopulations

**population subdivision reduces heterozygosity (perception)

-e.g. earth worms (poor dispersal abilities) –> 2 subpopulations vs. 1

Question 4

Wahlund effect

Answer 4

the perception of a heterozygote deficit caused by treating 2 separate subpopulations as a single population

Question 5

Fis

Answer 5

• quantifies the (avg reduction) changes in heterozygosity WITHIN subpopulations
• as a result of factors such as inbreeding, outbreeding, and assortative mating
• range: -1 to 1

-changes due to all factors: inbreeding, outbreeding, assortative mating

Question 6

Fst

Answer 6

• quantifies the proportion of the total reduction in expected heterozygosity at the metapopulation level, which occurs as result of population subdivision alone
• range: 0 to 1
• due to differences among subpop’ns (not w/in)
• def’n 2: proportion of total genetic variation in the metapopulation due to differences in allele freq’s among the subpop’ns

Question 7

Fit

Answer 7

• quantifies the total decrease in heterozygosity (HW deviation) at the metapopulation level as a result of:
  a) any deviations WITHIN each subpopulation (e.g. inbreeding, etc), and
  b) due to subdivision w/in the metapopulation

Question 8

Nei’s Genetic Distance (D)

Answer 8

• another way of measuring population differentiation
• the larger the value of Nei’s D, the greaterthe difference in allele frequencies among populations and subpopulations
• range: 0 to infinity

-in allozyme data: gives number of allelic substitutions at a locus

Question 9

Nst

Answer 9

• Fst variant
• advantage: unlike Fst, Nst can be used for haploid (as well as diploid)
• Fst only works for diploid

-considers both haplotype freq’s, and the sequence divergence b’w those haplotypes to quantify pop’n diff’s

Question 10

Gst

Answer 10

• Fst variant
• advantage: unlike Fst, Nst can be used for haploid (as well as diploid)

-considers only haplotype freq’s (diff’s among pop’s) to quantify pop’n diff’s

Question 11

If NST> GST:

Answer 11

genetically similar haplotypes co-occur w/in subpop’ns, but dissimilar haplotypes occur b/w pop’ns

Question 12

If NST< GST:

Answer 12

genetically divergent haplotypes co-occur w/in subpop’s, but at different frequencies

Question 13

contingency goodness of fit test

Answer 13

• a special variant of X2 (squared) test

- useful b/c it can be applied to any type of data: allozymes, microsatellites, and chloroplasts