Chapter 21: Population Genetics Flashcards
Natural selection is a mechanism of adaptive evolution based on what three things?
- phenotypic variation exists among individuals of spp.
- differences are passed on to offspring
- more offspring are born than survive in a pop^n
Phenotypic proportions change in the population after ?????
each generation
L> population allele frequency (Hz) also change.
Define Population in genetics terms ??
- group of interbreeding individuals of the same species that inhabit the same space at the same time
Define Gene pool!
- sum total of all alleles carried in all members of a population in one generation.
What is allelic frequency?
- proportion of all copies of a gene in a population that are of a given allele type.
L> Total # of gene copies= 2x individuals in pop
( ex: 16 in pop….2x16= 32 copies of CF gene)
L> heterozygotes contribute 1x for each allele
L> homozygotes contribute 2 x for desired allele.
For HIV what is the normal allele of the gene associated with its infection rate?
L> what about the mutated one?
CCR5-1
L> CCR5-delta32
HIV Infection rates:
- what do those with the mutated CCR5 allele not possess?
- CCR5 receptors
HIV Infection rates:
- Two exposed but uninfected individuals were homozygous for CC-CCR5 mutation on Chr.3. What does CC-CCR5 encode for?
- it encodes for chemokine receptor protein CCR5. CCR5 is also a receptor for HIV-1 strains.
HIV Infection rates:
- HIV-1 infection, explain.
- begins with binding of env proteins to CD4 receptor on the host cell. This causes the env to change chap and form a second binding site. This second site binds to CCR5 which will initiate fusion of the viral protein coat with the host cell membrane.
HIV Infection rates:
- The mutant allele of the CCR5 gene has a 32bp _____ in the coding region. The CCR5 mutant protein does/does not reach the host cell membrane.
- deletion
- does not
HIV Infection rates:
- HIV-1 env proteins bind to the CD4 receptors. A second site binds to ___ which will initiate the fusion of the protein coat with the host cell membrane. The mutant allele of the CCR5 gene has a 32bp ____ in the coding region.
- CCR5
- deletion
HIV Infection rates:
- What genotype= resistant to infection
- What genotype = AIDS progresses slowly
- What genotype= susceptibility to HIV-1 strains
- delta32/delta32
- 1/delta32=
- 1/1 homozygous
Hardy Weinberg Law??? (explain it generally)
- it clarifies the relationship between genotype and allele Hz within a generation and from one generation to the next. Assumptions have to be made with respect to the nature of the population, individuals within it and genes carried by the individual.
What are the assumptions for Hardy Weinberg? (5)
L> what is said when all five are met?
- infinitely large population
- random mating
- free from mutation
- free from migration (no gene flow)
- free from natural selection ( no genotype-phenotype differences in the ability to survive to reproductive age and pass on genes to the next generation)
* ** when all five are met the population will maintain genetic equilibrium and the frequency of each allele is conserved and the allele frequencies can be predicted!
In an infinitely large, randomly mating population, free from mutation, migration and natural selection; the frequencies of the alleles do/do not change over time where p =__, q=___ and the genotypic frequencies remain in the proportions p^2 (____), 2pq(___) and q^2(____). The sum of the genotype frequencies equals___. The overall binomial equation representing hardy weinberg is???
- do not
- —>The following are Hz of gametes
- p= frequency of A
- q= frequency of a
- —> The following are Hz of genotypes after mating
- p^2= frequency of AA
- q^2= frequency of aa
- 2pq= frequency of Aa
- 1
- equation: p+2pq+q= 1
- square root of p^2= Hz of dominant allele
What five things cause changes in allele frequency?
- mutation
- random genetic drift
- migration
- non random mating
- natural selection
Changes in allele frequency:
- migration and mutation increase/decrease genetic variation?
- increase
Changes in allele frequency:
- genetic drift increases/decreases genetic variation?
- decreases
Changes in allele frequency:
- Inbreeding leads to an increase/decrease in homozygosity and an increase/decrease in genetic variation ?
- increase
- decrease
Changes in allele frequency:
- Out breeding causes an increase/decrease in heterozygosity and an increase/decrease in genetic variation?
- increase
- increase
Changes in allele frequency:
- Natural selection can ____ genetic variation
L> OR through ____ and ____.
- increase and decrease genetic variation (one allele can be favoured over another and the other will be lost)
L> over dominance and balancing selection
Changes in Allele Hz: Genetic Drift: -increases/decreases allele Hz. - it results from??? L>formula? (effective population)
- decreases
- results from random events due to small population size. A population may be large but due to the number of breeding individuals the effective population may be small.
L> Ne= 4 x (Nf x Nm)/ (Nf + Nm)
L> progeny of a small pop will not show HW proportions
Changes in Allele Hz: Genetic Drift: - This decrease in allele Hz is caused by a small population size over many generations: L> Founder effect?? L>Bottleneck effect??
-FE: population is established by a small number of individuals
BE: population is dramatically reduced in size, genes lost from gene pool via chance. This reduction is due to tsunami, pandemic etc via natural disasters. The re-founding (FE) can occur only by the few that survive the BE .
*** The BE and FE are related! bottleneck occurs and then founder effect will remake population.
Changes in Allele Hz:
Effects of Genetic Drift?Explain.
L> also what does an Hz=0 and an Hz= 1 mean?
- causes changes in allele Hz over time in pop
- can cause loss of genetic variation in pop and reduces heterozygosity. Change in frequency over time is caused by chance in genetic drift, either increasing or decreasing.
L> 0= allele is lost
L> 1= allele has a fixed frequency