vocab

variations - differences in a species

• some are favourable (can help organism to survive & reproduce when they’re under selective pressures)

• variation has to be heritable in order to be passed on to the offspring

• over a period of time, the frequency of favourable variations in a population will increase, while frequency of unfavourable traits decreases

• is known as natural selection

natural selection - the process in which different environments influences survival & reproduction of organisms due to the existence of variations

genetic variation - the differences in genomes in individuals of same species

• arises due to mutations & sexual reproduction

limiting factors - a resource in an environment that can affect a population size if the resource becomes limited

• ex: food, space, water

• also determines carrying capacity of environment

carrying capacity - the maximum population size of a species that an environment can sustain

density-independent factors - abiotic factors that impact the size of a population, regardless of the population density

• so they affect all populations, regardless of their density

• ex: global-warming has impacted polar bears, regardless of their population density

density-dependent factors - abiotic factors that vary in severity, depending on population density

• tend to hv stronger effect as population density increases

• ex: competition for resources, predation

biological fitness - the ability of an organism to reproduce & pass on its genetic material to offspring

• is determined by:

  • the environment the genotype lives in

  • survival value of an individual

  • reproductive potential of an individual

intraspecific competition - individuals of same species compete for resources

• is density dependent (increase in population size = increase in competition for resources)

interspecific competition - competition for resources between different species

sexual selection - special case of natural selection, with focus on finding a mate & reproducing

• can be intrasexual selection or intersexual selection

intrasexual selection - competition between individuals of one sex to mate with individuals of other sex

• typically male-male competition

• ex: contests of strength in male deer

intersexual selection - individuals of one sex (typically females) choose an individual of the opposite sex as their mate

• they exert strong selective pressures on the opposite sex

• ex: courtship dances, elaborate plumage, mating calls

gene pool - the sum total of all the population’s genes & their different alleles at a given time

• changes through evolution

• large gene pools = indicative of extensive genetic variation

  • means the population will be better adapted to different environments (cuz they hv genes that provide them with advantages to survive)

allele frequency - relative frequency of a particular allele in a population

• 0 = allele isnt present in population

• 1 = present in all individuals

• can be the result of directional, stabilizing or disruptive selection

directional selection - favours one extreme phenotype over others

stabilizing selection - favours middle phenotypes

• most individuals will look similar to each other = less genetic variation

disruptive selection - favours both extreme phenotypes over middle phenotype

• over time, could result in formation of new species