lecture 11 Flashcards
what is inbreeding
a form of non random mating
make new assumptions = modify hardy weinberg
describe inbreeding - context of crosses
same allele being passed down
mating between first cousins
many possibilityes
what is IBD
alleles that are IDENTICAL BY DESCENT (IBD) are one possible outcome
at single locus
what inbreeding increase
Probability that 2 alleles at a locus will be copies of an allele present in an ancestor
such copies = IBD - identical by descent
what is F coeff
probability of IBD
F quantifies the overall probability that the two alleles inherited by a given individual will be identical by descent
how to calculate inbreeding coeff
locate individual and diagram pathway
people in pathway besides final person = n
inbreeding coeff F= (1/2)^n
(if 2 paths = add both coeffs together)
if parent is inbred = modified formula F = (1/2)^n (1+FA), where FA = inbreeding coeff of parent
what changes genotype frequencies
inbreeding
describe frequencies in changed inbreeding frequencies
in pop that switches over from random mating to inbreeding
fA1A1 = p^2 +Fpq
fA1A2 = 2pq (1-F)
fA2A2 = q^2 + Fpq
more homozygotes and LESS heterozygous
as F increases heterozygous decrease and homozygous increase (if more and more gens = further depart from hardy weinberg)
what is inbreeding depression
reduction in viability of inbred individuals
why does inbreeding depression happen
bc most deleterious conditions require 2 copies of mutation to be expressed
so more and more diseases expressed
reduces vigor, variablity and reproductive sucess
decline in fitness of average individual
what is inbreeding mortality in us
more and more inbred (like the more closely related) = increase infant mortality
does inbreeding cause change in allele frequencies
NOOOO
but genotype frequencies do change
name factors influencing allele frequencies
mutation
Migration
genetic drift
natural selection
describe mutation - factors influencing allele frequencies
ex = Mutations at the Cystic Fibrosis Transmembrane Conductance (CFTR)
locus can lead to Cystic Fibrosis
Particular mutation on chrom 7 cftr gene at base pair level
what is a typical rate of mutation per base pair of dna per gen in humans
one in a billion
low rate of mutation depends if talking about gene or nt but still v small
how quickly does mutation alone change allele frequencies
mutation rate = 10^-5 per gen
p t+1 = p t (1-u)
veryyyy slowly
mutations alone have small effect
describe migration - factors influencing allele frequencies
could be higher than mutations = will change it faster
introduces new allele into group
if unidirectional = like mutation
if bidirectional = homogenizes population= does not diverge
describe genetic drift - factors influencing allele frequencies
small pops - just drifting
if large pop = not drift as much
small pop = can diverge quickly from hardy weinberg - loss of fixation of genetic alleles, diverges from each other in allele frequencies, wild fluctuations in allele freq
where is random genetic drift weakest and explain
large population= no extreme genetic drift
small pop= divergence from one another and loss of genetic diversity
if have high migration = populations would diverge less quickly since slows down loss of alleles since creates larger pop
describe population bottlenecks
smaller neck into bigger bottle = wont contain same proportions as small bottle
describe island colonization from mainland
founding pop from larger pop
pop smaller for individual islands = could lead to genetic drift can end up with diff composition - can lead to bottleneck effect
describe population crashes
hare population grows and lynxs follows
if lynxs grow a lot = hare as food goes down = now lynx crashes
sort of bottleneck event
overtime pop represents genetic mean = closer to smaller pop (human pop looks smaller genetically -diversity)
describe ex of genetic drift - retinitis pigmentosa
regular = 1/2000 individuals have diseases usually but
tristan de cuhna island = frequency 10-20 times higher since one pop has more of it
describe ex of genetic drift - CF
Average Cystic Fibrosis incidence worldwide (1 out of 2,500), but in Saguenay region of Quebec (1 out of 936)
large fluctuation in allele frequency
What else happen in populations that are kept small for generation after generation?
loses variation and increases inbreeding coeff
inbreeding levels building up fast in smaller pop
what can habitat fragmentation do
reduce population sizes
natural lanscape divided up into smaller and smaller fragments
leads to small pop size - no migration between habitats
more and more rare alleles being lost - lose genetic diversity
like adaptations for global warming lost = cannot survive well, so small population disadvantaged
describe small populations and the extinction vortex
small pop leads to small pop
could have effect on size of future pop
inbreeding leads to reduction of health, individual fitness and inability to adapt, possible feedback loop
each gen = worse = lost more variability and suffers from inbreeding depression = extinction vortex
what happens if homozygous selected against
bad like purging
selecting against = both inbreeding and selection
