Evolution of Populations
Evolution is a change in the allele
frequency of a population.
TERMS TO REVIEW: gene, chromosome,
homologous chromosomes (Image), allele, locus
(loci), haploid,
diploid, phenotype,
genotype, dominant, recessive, homozygous, heterozygous
Population Genetics
Study of the properties of genes within populations
Puts together Darwinism and Mendelian inheritance
Evolution results from changes in allele frequency
Population
Species
Gene pool
The Hardy-Weinberg
Theorem
States that there will
be no change in allele frequencies in a population if the following 5
conditions are maintained:
Very large population
No migration
No mutations
Random mating
No natural selection
In a population meeting
all these conditions, no evolution is occurring. It is in Hardy-Weinberg
equilibrium.
All these conditions
are never met.
The Hardy-Weinberg Equation
- Image
and Image.
Frequency of dominant allele = p
Frequency of recessive allele = q
p + q = 1
To represent the individual which has received one allele from each parent:
(p + q)2 = p2 + 2pq + q2 = 1 (the small 2 represents "squared")
Microevolution: Why
Do Allele Frequencies Change? Table 17.1a
and Table
17.1b
Genetic Drift - change in frequency or even loss of alleles in small populations compared to large ones. Image
Bottle neck effect - image
Founder principle Fig. 17.12
Natural Selection
Forms of Selection. Fig. 17.13-
summary of 3
forms: Image
or Image
Stabilizing selection and heterozygote advantage Stabilizing selection: sickle-cell anemia (Fig. 17.16) and malaria- Fig 17.17
Directional selection. Fig. 17.14c Fig 17.18 and Fig 17.19
Selection In Action
Individuals best suited to environment are most likely to survive, mate and leave the most progeny
Individuals are selected, but populations evolve.
Individual alleles make varying contributions to fitness
Only natural selection produces adaptive evolutionary change
