Topic 2: Hardy-Weinberg Principle Flashcards
evolution definition (2)
1) descent with modification
2) change in population allele frequencies
in random mating, if genotype frequencies at a locus are:
AA = 0.26
AB = 0.47
BB = 0.27
what’re the probabilities that an individual will mate with an individual w/ these genotypes?
same as genotype frequency!
ex. probability for AA = 0.26
assumptions: genotypes frequencies are same among males and females, pop is infinitely large
random mating is equivalent to ____ ____ of _____
random union of gametes
probability that 2 gametes (alleles) unite to form a zygote (diploid genotype) is equal to ____________
product of their allele frequencies
8 assumptions of HW principle
- random/panmictic mating
- non-overlapping generations
(parents die after offspring are born. mostly robust even if this is violated) - diploid
- strictly sexual reproduction
- large pop
- negligible migration
- no genetic mutations
- unaffected by natural selection
how long does it take to restore HW equil?
one round of random mating to restore expected HW genotype frequencies
Without violating HW assumptions, genotype and allele frequencies will _____?
allele frequencies will not change
- no evolution will occur!
ex. when calculating the expected genotype freq in next and current gen, we only need to do it once because it shouldn’t change :)
with deleterious recessive alleles, is HW principle still valid?
No! natural selection is working against these alleles
HW disequil is always a result of either ____ ___ or _____ _____
heterozygote deficit
or
heterozygote excess
type I vs type II statistical error
type I: rejecting null hypothesis when true
type II: accepting null hypothesis when false
parthenogenesis = ?
- female clonal reproduction
- development of an egg w/o paternal contribution
obligate parthenogenesis = ?
- species consists of females only; eggs never develop into males, hence never sexual reproduction
cyclical parthenogenesis = ?
- male develop from eggs at some point, resulting in sexual reproduction;
- which produces an all-female pop that reproduces clonally (most of time)
morphological species concept vs
biological species concept
morphological species concept
- individuals are considered to belong to the same species if they agree morphologically with the “type” of the species
biological species concept
- species are groups of interbreeding natural pops that are reproductively isolated from other such groups
morphologically cryptic species
different biological species
don’t reproduce together
ex. (AA, AB, BB, CC)
never any AC or BC heterozygotes! evidence of morphologically cryptic species
cryptic biological species (sometimes called sibling species) can usu only be identified by?
genetic methods
what factors can cause HW disequil (9)?
what do not cause HW disequil (2)?
- natural selection: het excess or deficit
- inbreeding: het deficit
- outbreeding: het excess
- assortative mating: het excess or deficit
- asexual reproduction: het excess or deficit
- cryptic species: het deficit
- gene flow and migration: het excess or deficit
- pop bottlenecks: het excess or deficit
- founder effects: het excess or deficit
DOES NOT CAUSE HW DISEQUIL:
- genetic drift: HW assumptions
- mutations: HW assumptions
challenges with HW principles (X2) null hypotheses
microsatellites
- hyper-variable locus
– solution: data can be lumped into 2 classes, hets and homos
- null alleles
– will appearance of het deficit when it does not exist (hets look homo bc only one allele amplifies)
next generation seq
- SNPs, a lot of loci -> easy to reject null hypothesis when true
– solution: Bonferroni correction (BC)
adjust statistical significance lvl (0.05) by dividing it by # tests we conduct (increases type II error)
- allelic drop out (ADO)
detection of only one of two alleles (primer bias, random sampling error, etc.); like null alleles in microsatellites
- accidental het excess is common in NGS
for humans, females are ____ sex and males are ____ sex
homogametic
heterogametic
