IB 446 Exam 2

Natural Selection

process by which favorable heritable traits become more common in successive generations of a population

Relative fitness

relative ability of different genotypes to pass on their alleles to future generations

Basic selection model

uses simplifying assumptions to examine dynamics of genetic change caused by selection and statics of genetic variation

Heterozygote advantage/overdominance

homozygotes have selective disadvantage over heterozygotes, stable condition ex) sickle cell anemia where heterozygotes are more resistant to malaria

Heterozygote disadvantage/underdominance

homozygotes have selective advantage over heterozygotes, unstable condition

Fisher’s fundamental theorem of natural selection

rate of increase in fitness of any organism at any time is equal to its genetic variance in fitness at that time

Selection coefficient (s)

measures amount of selection against a homozygote

Level of dominance (h)

when multiplied by s measures amount of selection against heterozygote

Purifying selection

focus is on reduction in frequency of detrimental allele A2. Lethal allele has s=1 and fitness of 0. Detrimental alleles have s= 0 to 1 and fitness from 1 to 0.

Adaptive/positive Darwinian selection

focus is on increase in frequency of beneficial allele A1

Genetic load

reduction in fitness from what the population would have if all individuals has the most favored genotype. Due segregation of homozygotes when there is a heterozygous advantage.

Viability selection

survival of different pre-adult stages ex) Rh blood factor where Rh antigen present on surface of red blood cells if Rh+. Fetal mortality occurs when mother is Rh- while fetus is Rh+ since the father was Rh+ (also example of underdominance)

Sexual selection

some male or female genotypes favored for mating, often involves male competition or female chouce

Gametic selection

gametes from heterozygotes are not in equal proportions

Fecundity selection

one genotype is more fertile than another

Antagonistic pleiotropy

negative correlation of two components of fitness, single locus affects multiple selection components in opposite directions ex) senescence alleles that increase fitness in younger organism but contribute to decreased fitness in aged organism

Sexually antagonistic genes

genes that have opposite selective effects in females and males

Meiotic drive or segregation distortion

gametes produced from heterozygotes are not equal in proportions ex) t locus in mouse chromosome 17 where alleles are lethal in homozygous

Positive assortative mating

similar individuals mate more often than randomly expected, results in no change of allele frequency but an increase in homozygosity

Negative assortative mating

individuals with unlike genotypes mate more often than randomly expected, leading to higher heterozygosity

Self-incompatibility alleles

prevent self fertilization in plants resulting in an absence of germination from the same or similar plants. 2 types: gametophytic and sporophytic

Gametophytic self-incompatibility

pollen has different allele from female plant

Sporophytic self-incompatibility

results from genotype of the male parent

Frequency dependent selection

more fitness due to level of frequency in the population, positive frequency dependent selection is when there is selection against lower frequency variant (ex: rare flower not recognized by pollinator leading to faster fixation of common alleles)

Positive frequency dependent selection

when there is selection against lower frequency variant (ex: rare flower not recognized by pollinator leading to faster fixation of common alleles)

Negative frequency dependent selection

when selection is against higher frequency variants ex) right or left “handedness” of scale eating cichlid

Ecological genetics

assumes that selective values are environmentally dependent and that the environment may vary over time and space

Spatial or temporal variation

fitness varies over time or space

Habitat selection

individuals prefer ecological niches in which they have better fitness

Coevolution

evolution that occurs as a result of different species responding to each other

Host-pathogen interactions

interactions of pathogens and their hosts may result in frequency-dependent selection

Evolutionary arms race/red queen

continuing development is needed to maintain fitness relative to systems it is coevolving with (ex: prey evolves to run faster so predator evolves to run faster)

Relative risk

ratio of probability of an event occurring in a group exposed to an agent versus the risk of the event occurring in a non-exposed group

Outbreeding

reproduction among unrelated individuals

Inbreeding

reproduction among relatives

Coefficient of inbreeding (f)

probability that 2 homologous alleles are IBD

Identical by descent (IBD)

two alleles in an individual are derived from the same chromosome carried by a recent common ancestor present in both parents

Identity in state

2 homologous alleles are not derived from same chromosome of a recent common ancestor

Assortative mating

mated pairs in a population are composed of the same phenotype more often or less often than expected by chance

Sexual imprinting

in birds, individuals with a phenotype similar to maternal phenotype of preferred which usually leads to positive assortative mating

Coefficient of relationship, r

the fraction of alleles between 2 individuals that are IBD. For non-inbred diploids, it is 2x f

Kinship coefficient

probability that alleles drawn at random between 2 individuals are IBD. Equal to f of an offspring from them

Philopatry

tendency of progeny to remain near their natal territory

Kin selection

selection acts through effects of close relatives, may allow altruistic behavior

Altruism

when an individual sacrifices some fitness to increase fitness of others

Inclusive fitness

fitness of an individual+their effect on relatives weighted by their coefficient of relationship

Inbreeding depression

decline in fitness due to inbreeding, difference in fitness between outbred and inbred populations

Purging

deleterious recessive “a” present in a population at low frequencies in heterozygotes so the phenotype is not expressed. Inbreeding decreases proportion of Aa and increases AA. aa is then purged from population

Number of lethal equivalents

cumulative effect in deaths that would result if genes with deleterious recessive alleles in a heterozygote were made homozygous