Lecture 33 Flashcards
Measuring variation in a population
- Visible differences in phenotype
- Chromosome differences (eg. length of long arm of Y)
- immunological markers (eg. blood groups)
- protein gel electrophoresis (eg. esterases in Dros)
- SSLPs (simple sequence length polymorphisms) or VNTR (variable number of tandem repeats)
- STR or (short tandem repeats)
- Single nucleotide polymorphisms (SNP)
Molecular level variation
Minisatellites (15-100b eg. tandem repeat of 18 bases) VNTR
Microstatellites (short tandem repeats 2-9 bases
Single nucleotide polymorphisms (1 base) - can be detected by DNA sequencing, restriction cutting sites
(Varies between people so can be used to find variations in people)
Multilocus probe
Single locus probe
Multilocus probe is found in more than one location (minisatellites)
Single is
Used to…
parentage, crime, victim indent, animal indent, conservation biology
To calculate allele frequency when heterozygote can be recognised
homo x2 + hetero x1
over (total) x2
When complete dominance and heterozygote same pheno as homozygote
assume hardy-weinberg equilibrium which is that genotypes are in proportions if p=f(A) allele q=f(a) allele. p^2=f(AA), 2pq=f(Aa), q^2=f(aa)
The Hardy-Weinberg Equilibrium
p^2+2pq+q^2 = 1
Assumption of H-W Equil
1) Random mating
2) no migration (no gene flow)
3) no selection acting (everyone equally likely to have same amount of babies
4) no mutation
5) infinite population size
When not HW
and trait is autosomal, is can be restored in one generation of random mating NOT so for an x-linked trait
Selection not controlled for
May sig. alter allele frequencies or hold them constant Relative fitness (w) - 0 if condition is lethal or no offspring produced 1 for genotype leaving most offspring Selection coefficient is s relative fitness = 1 - s if s=1 all dead (as selection increases fitness decreases)
Selection can be changed by the envirionment
climate, pollution, predators, disease, insecticide
Stabilizing selection
selection against the extremes in the phenotype
Disruptive selection
selection against the intermediate phenotypes
Directional selection
selection for one phenotype from the end of the phenotypic range
Mutation
- very little effect to allele frequencies on its own
- source of all new alleles
- w/ selection can be significant
Migration (gene flow)
may be significant depending on m and difference between x and p (&p = m(x-p)
Non-random mating
- inbreeding, consanguinity, self-fertilisation –> mating between related indiv. (genetic relationship, alters genotypic ratios by increasing homozygosity)
- Assortative mating (AM)
- -> select individuals like themselves (positive AM)
- -> select indivduals unlike themselves (negative AM, increase heterozygosity)
Population size
may be significant
- random changes in allele frequencies due to sampling error
- occurs in all populations but effect pronounced in small populations
Founder effect
small group from a larger population settle in a new location
Bottleneck
population goes through a severe reduction and only a few members survive to produce next generations
Speciation
separation of gene pools
- Allopatric (physical barrier separates gene pools)
- Sympatric (separation of gene pools occurs in the same area)
Reproductive Isolation
Prezygotic mechanisms: prevent fertilisaiton and zygote formation
1) habitat - geographic or ecological isolation
2) seasonal or temporal
3) ethological/behavioural (courtship)
4) mechanical
5) physiological (gametes make it to female but do not survive)
Post-zygotic mechanisms
1) hybrid inviability or breakdown
2) Developmental hybrid sterility
3) F^2 breakdown
