Module 11: Evolution

theory of evolution

existing species descended from ancestral species with modifications; natural selection is the mechanism of evolution

natural selection can only take place if there’s…

variation

genetic diversity in a population comes from two main sources…

mutation and sexual reproduction

mutation

any change in the DNA sequence of a cell

adaptation

evolutionary process where an organism becomes better able to live in its habitat

divergent evolution

two species evolve in different directions from a common point

convergent evolution

organisms that aren’t closely related evolve similar features/behaviors

population

a group of individuals of the same species that live in the same area and interbreed

gene pool

sum of a population’s genetic material at a given time

hardy-weinberg formula

p² + 2pq = q² = 1, used to calculate the frequencies of genotypes in a gene pool from the frequencies of alleles

mechanisms that alter allele frequencies in a population

natural selection, mutation, genetic drift, gene flow

genetic drift

can lead to the elimination of an allele from a population by chance

bottleneck effect

a chance event or catastrophe that reduces the genetic variability within a population

founder effect

when a small group breaks off from a larger population, leading to less genetic diversity in the new group

gene flow

when individuals from different populations breed and mix their genes

homology

when different species share similar traits because they inherit them from the same ancestor

vestigial structures

unused structures without function

analogous

similar or corresponding in some respect

biological species concept

defines species based on their potential to interbreed and produce fertile offspring

speciation

formation of new species, occurs when some individuals can no longer interbreed with the rest of the group

reproductive isolation

what keeps species from mixing through breeding

prezygotic reproductive barriers

prevent fertilization before an egg can form

postzygotic reproductive barriers

when a baby is formed, but it can’t survive well or can’t have babies of its own

reproductive barriers arise in two ways:

allopatric speciation, sympatric speciation

allopatric speciation

when species split and change because they’re separated by geography

sympatric speciation

when new species form while living in the same place

aneuploidy

too many or too few chromosomes

autopolyploidy

when a species gets too many of its own chromosomes

allopolyploid

when an organism gets chromosomes from two species, not just one

sympatric speciation occurs…

when gametes unite to form polyploid offspring with more chromosomes than either parent