LO3/LO4 Terms

speciation

process by which populations evolve into new species

occurs when a group within a species separates from other members and develops its own unique traits

species

group of populations whose members have the potential to interbreed in nature and produce viable, fertile offspring

are unable to do so with other group members

united by being reproductively compatible

prezygotic barriers

reproductive barriers that prevent mating between species or block fertilization if mating is completed successfully

postzygotic barriers

reproductive barriers that prevent hybrid zygotes produced by different species from developing into viable, fertile adults

habitat isolation

two species that live in different habitats are less likely to encounter each other

temporal isolation

species that breed during different times

behavioral isolation

courtship rituals that attract mates (unique to a species)

mechanical isolation

mating is attempted but morphological differences prevent completion

gametic isolation

sperm of one species cannot fertilize the eggs of another species (sperm might be unable to survive in the reproductive tract of females)

reduced hybrid viability

genes of different parent species may interact in ways that impair the hybrid’s development or survival in its environment

reduced hybrid fertility

if chromosomes of parent species differ in number or species, meiosis in hybrids may not produce normal gametes

hybrid breakdown

some 1st gen hybrids are viable and fertile but when mated with one another, offspring are sterile and feeble

allopatric speciation

gene flow is interrupted when a population is divided into geographically isolated subpopulations

formidability of geographic barrier is dependent isolated subpopulations

sympatric speciation

speciation occurs in populations that live in same geographic area

what are the three ways sympatric speciation can occur in species that live in the same geographic area?

this can occur if gene flow is reduced by polyploidy, habitat differentiation, and sexual selection

features of natural selection

variation within population

inheritance of traits

overproduction of offspring

differential survival and reproduction

gene pool

the collective set of all genes, including different variations (alleles), present within a population of a specific species

conditions for hardy weinberg

no mutations

random mating

no natural selection

extremely large population size

no gene flow

founder effect

occurs when a few individuals become isolated from a larger population and establishes a new population whose gene pool is different from the source population

bottleneck effect

occurs when a population is drastically reduced as a result of a natural disaster or sudden change in environment

effects of genetic drift

significant in small populations: chance events can cause an allele to be disproportionately over or under represented

can cause allele frequencies to change at random

can lead to loss of genetic variation

can cause harmful alleles to be fixed

usually occurs when population is small

stabilizing selection

favoring intermediate variants

directional selection

occurs when conditions favor individuals that show one extreme of a phenotypic range

disruptive selection

occurs when conditions favor individuals at both extremes of a phenotypic range

frequency dependent selection

fitness of a phenotype is dependent on how common it is in the population

heterozygote advantage

greater reproductive success of heterozygous individuals compared with homozygotes tend to preserve variation in a gene pool