Zoology 152 - Evolution

biogeography

the geographic distribution of living organisms

common ancestry

the concept that if you trace back the lineages of living species far enough in time, those species will converge to a shared ancestor

evolution

the change in frequency of genetic variants in a population

fixation

the loss of variants except one from a population

homology

traits whose similarities are explained by common ancestry

natural selection

the tendency for genetic variants that enhance fitness to go to fixation and variants that reduce fitness to be lose from populations

nested hierarchy

a pattern of groups nested within groups (without overlaps) as seen in taxonomies

polymorphism

the existence of multiple variants within a population

transitional fossil

fossil taxa that have some, but not all, of the derived traits of a living group

allele frequency

in a population, the proportion of all alleles at a locus that are of a particular type

allele

a particular variant of a gene

diploid

the trait of having two sets of chromosomes, as in humans

evolution

change in the genetic composition of a population over time

fixed

an allele that has a frequency of 1.0 in a population

genotype

genetic makeup of an organism

haploid

the trait of having one set of chromosomes in an organism

hardy-weinberg law

the law that, when a few key assumptions hold, makes it is possible to predict the genotype frequencies in a population for the next generation, based on the allele frequencies in the current generation 

locus

a place in the genome where alleles reside; in diploids, each individual has two alleles per locus

phenotype

the physical and behavioral characteristics of an organism that result from the interaction of the organism’s genotype and its environment

polymorphic

when more than one allele is found at a given locus in a popiulation

populations

a group of interbreeding organisms

selfing

when an organism reproduces with itself, providing both the egg and sperm components

beneficial mutation

new allele that enhances the fitness of an organism

deleterious mutation

new allele that decreases organismal fitness

directional selection

selection that arises when one allele consistetntly raises fitness; eventually the beneficial allele is expected to become fixed in teh population

mutation

a change in a gene sequence; arises independent of the needs of an organism

natural selection

process of allele frequency change due to fitness variation among genotypes at that locus

neutral mutation

a new allele with neither a beneficial nor a deleterious effect

relative fitness

the fitness of a given genotype divided by the fitness of a reference genotype which relative fitness is assigned to be 1.0

genetic bottleneck

The phenomenon in which a population lineage shrinks to a small size for a period, causing that population to lose genetic variation

genetic drift

Random change in allele frequencies in a population over time

genetic load

The frequency of deleterious alleles that have accumulated in a population

carrier

an individual who is heterozygous for a disease

overdominant selection

selection in which heterozygote genotypes have the highest fitness

trans-specific polymorphisms

a set of alleles that are shared between closely related species; they arose before speciation and were maintained as polymorphisms

underdominant selection

selection in which heterozygote genotypes have the lowest fitness

continuous traits

traits characterized by values on a continuous scale, rather than being controlled by a single locus (height, weight, hair length, etc.)

eugenics

the misguided and unethical attempt to increase the frequency of '“desireable” traits in humans using evolutionary principles

response to selection - r

the amount the mean trait value in a population changes after one generation

standard deviation

square root of the variance

heritability (h squared)

the fraction of the variation of the population that can be explained by genetics

variance

a measure of the spread of the distribution of a trait values in a population (technically the sum of the squared deviations from the mean value)

continuous trait

trait characterized by values on a continuous scale, rather than being controlled by a single locus

disruptive selection

selection that favors trait values at both extremes of the trait value distribution

stabilizing selection

selection that disfavors extreme trait values and favors trait values towards the center of the trait distribution