4: Intro to pop genetics Flashcards
define locus/loci
physical position of a gene or marker along a chromosome
define allele
different forms of a gene
Define genotype
in diploid organisms, 2 alleles make up the genotype
define heterozygote
individual with 2 different alleles (Ww)
define homozygote
individual with 2 identical alleles (e.g WW or ww)
define polymorphism
gene or phenotype with more than one form
Describe the Hardy-Weinberg equilibrium
Allele frequencies in one generation can be used to predict genotype frequencies in the next generation
P2 + 2pq + q2 = 1
P + q = 1
What are the assumptions of HWE?
Random mating
No natural selection
Large pop. size
No migration
No mutation
= in real world these assumptions will probably not be met
Why is HWE useful?
Provided a description of how genetic variation is maintained
Under HWE assumptions, the frequencies are constant over time
Used to show how blending inheritance doesn’t happen
Departures from HWE mean that some assumptions aren’t met
Something interesting must be going on e.g selection
Useful in medical genetics
What are the 4 steps in calculating departures from HWE?
- Estimate allele frequencies
- Calculate expected frequencies under HWE
- Calculate expected genotype counts in the sample
- Calculate chi-squared
What does chi-sqaured measure?
→ measure of goodness of fit
Larger values = larger departures from expectation (significantly different)
Give an example of how non-random mating can cause significant departures from HWE.
Inuit and African American allele frequencies
What does the chi squared test measure?
Goodness of fit
Larger values = larger departures from expectation (significantly different)
Give a real world example of migration causing gene flow
Introduction of european genes into African pop.s = caused by the slave trade
What is expected heterozygosity (2pq)?
a measure of the level of variability at a locus
→ little variability in source pop.s
→ admixed pop. are more diverse
