Microevolution: Gene pools and allele frequencies

Evolutionary success or fitness

refers to the contribution of genes to the gene pool and NOT how long an organism lives.

Evolution

a change in the inherited characteristics of biological populations over successive generations.

Microevolution

simply a change in gene frequency within a population.
Evolution at this scale can be observed over short periods of time such as from one generation to the next.

gene

a sequence of DNA nucleotides that specify a particular polypeptide chain.

Macroevolution

evolution on a scale of separated gene pools (not individuals).

Gene pool

sum total of all the genes in a given species

Allelic frequency

the percent occurrence for a given allele

Mutations and Meiosis and sexual reproduction

How does variation in a population or gene pool arise?

MOST mutations

deleterious as well as recessive.

frameshift mutation

occurs as a result of either an insertion or deletion of a nucleotide.

Microevolution

mutation, selection (natural and artificial), gene flow, and genetic drift.

Genetic drift or allelic drift

the change in the frequency of a gene variant (allele) in a population due to random sampling in the absence of a selection pressure.

Nonrandom mating and sexual selection

also changes allele frequency.

Natural Selection

the only mechanism that consistently causes adaptive evolution.

Relative fitness

defined as the contribution an individual makes to the gene pool of the next generation relative to the contributions of other individuals.

sexual dimorphism

which is a difference between the two sexes with regard to secondary sexual characteristics.

Intrasexual

election within the same sex, individuals of one sex compete directly for mates of the opposite sex. Males are famous for this!

Intersexual selection (mate choice)

individuals of one sex are choosy.

neutral variation

differences in DNA sequence that do not confer a selective advantage or disadvantage.

to reduce variation

Diploidy
Balancing Selection
Hererzygote Advantage
Frequency-Dependent Selection

Diploidy

diploid eukaryotes each organism has two copies of every gene and a considerable amount of genetic variation is hidden from selection in the form of recessive alleles.

Balancing selection

occurs when natural selection maintains two or more forms in a population. 

Frequency-Dependent Selection

The fitness of a phenotype depends on how common it is in the population.

positive frequency-dependent selection

the fitness of a phenotype increases as it becomes more common.

negative frequency-dependent selection

the fitness of a phenotype increases as it becomes less common.

Balanced polymorphism

occurs in a given population when two distinct types (or morphs) exists and the allele frequencies do not change.

Selection can act only on existing variations.
Evolution is limited by historical constraints.

Why Natural Selection Cannot Fashion Perfect Organisms

Adaptations are often compromises.

The loud call that enables a frog to attract mates also attracts predators.

Chance, natural selection and the environment  interact.

Chance can affect the subsequent evolutionary history of populations. A storm can blow birds hundreds of kilometers over an ocean to an island, the wind does not necessarily transport those individuals that are best suited to the environment!