genetic diversity and natural selection

what causes variation

genetics (mutations, sexual reproduction), environment, epigenetics

continuous variation

2 extremes and a full range of intermediates, caused by combination of multiple genes and environment

discontinuous variation

two or more discrete categories with no intermediate values, caused by a single gene

genetic diversity

the number of different alleles of genes/a gene in a population

individual selection (type of natural selection)

factors determining the number of offspring produced by an individual over its lifetime

sexual selection (type of natural selection)

members of one sex choose who to mate with, leading to higher reproductive success in some over others

kin selection (type of natural selection)

reproductive success of relatives is favoured over survival of individuals

natural selection

process by which organsims that are better adapted to their environment tend to survive and breed

directional selection

phenotypes at 1 extreme of the population being selected for and those at the other extreme being selected against, causes a shift in mean of any given trait

how does directional selection occur

those with extreme adaptations survive more when environment changes, those with less extreme allele die, less competition so those with extreme adaptation breed more and pass on advantageous allele, frequency of advantageous allele and phenotype increases in population, mean allele shifts in this direction

stabilising selection

phenotypes around mean of population being selected for and those at both extreemes being selected against, no shift in mean of trait

how does stabilising selection occur

those with extreme adaptations die as environment is constant, those with allele for mean characteristic survive more, less competition so those with mean characteristic breed and pass on advantageous allele, range of allele types is decreased, increased frequency of mean allele and phenotype in population

population

group of naturally occurring members of the same species which can freely interbreed to produce viable offspring

disruptive/diversifying selection

extreme values for a trait are favoured over intermediate values

genetic drift

variation in relative frequency of diff genotypes in a small population, owing to the chance disappearance of particular genes as individuals die or do not reproduce

types of adaptation

anatomical, physiological, behavioural

founder effect

small group of individuals may migrate/become isolated from a population, founding pop is small, possible problem of inbreeding, may have non-representing sample of alleles from parent pop, colonising pop may evolve differently from original pop if environment is different, certain alleles go missing as a consequence, loss of genetic diversity

bottleneck effect

ecological events reduce pop size dramatically, these disasters are unselective, small surviving pop unlikely to be representative of original pop, by chance alleles may be overrepresented among survivors, others completely eliminated