week 2(ch 26 &27)
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a group of individuals from the same species that live in the same area at the same time and can interbreed
population
a group of all the alleles from all the gametes produced in each generation
gene pool
equation for allele frequencies
p + q = 1
equation for genotype frequencies
p^2+ 2pq+ q^2 = 1
Hardy-Wienberg’s assumptions
• random mating • no natural selection 3.no genetic drift 4 no gene flow 5 no mutation
inbreeding causes — to increase, but does not change—-
inbreeding causes homozygosity to increase, but does not change allele frequencies
alleles that lower fitness
deleterious alleles
inbreeding does not cause evolution, but it can…
increase the rate at which deleterious alleles are eliminated
what are two reasons why inbreeding depression occur?
• many recessive alleles represent loss of function mutations ( are bad) • many genes that are involved in fighting disease need heterozygote
the number and relative frequency of alleles that are present in a particular population
genetic variation
changes the average value of a trait because individuals at one end of the distribution experience low reproductive success
directional selection
reduces the variation of a trait, but keeps the average value constant eg. Weight of baby
stabilizing selection
extreme phenotypes are favored. increases the amount of genetic variation
disruptive selection eg only birds with extremely short or extremely long necks survive
disruptive selection sometimes plays a role in…
speciation!
when no single phenotype is favored; genetic variation is maintained
balancing selection
when an individual of one gender selects for an individual of another gender
intersexual selection
when selection occurs within two organisms of the same gender eg. giraffes fighting or seals fighting
intrasexual selection
any trait that differs between males and females eg. Mallards
sexual dimorphism
any change in allele frequency due to chance
genetic drift aka sampling error
genetic drift occurs especially in
small populations
over time genetic drift can lead to…
the random loss or fixation of alleles
a change in allele frequency that occurs when a new population is established
founder effect
when a large population experiences a sudden reduction in size
genetic bottleneck
occurs when an individual leaves one population, joins another, and breeds
gene flow