evolution exam 2

assortative mating

nonrandom mating due to mate-choice

positive assortative mating

prefer to mate with individual with same genotype (can lead to speciation)

negative assortative mating

prefer to mate with individual with different genotype (diversifies the gene pool)

wahlund effect

less opportunity for genetic mixing

reduction in heterozygosity within a total population it occurs when separate subpopulations have different allele frequencies and are mistakenly sampled or grouped as a single large population

mainland island model

one way migration model

alleles on island are same as yesterday except for new ones that come over from the mainland and replaced old ones

finite island model

all populations are discrete island (no mainland)

some migration rate in both directions

same size populations

different allele frequencies on each island

will reach equilibrium

genetic drift

result of sampling, accumulation of chance changes in allele frequency due to random sampling/ smaller populations are more affected

fixation

when one allele reaches a frequency of 100%

ex. drift

forces which reduce genetic diversity

genetic drift

bottleneck

founder effect

bottleneck

sharp reduction in population size that leads to massive loss of genetic diversity

period during which only a few individuals survive to continue the existence of the population

founder effect

the original population has more genetic diversity than the newly founded population because the new population is started by a very small group of individuals and they brought a small amount of diversity with them

populations descended from a smaller founder group may have low genetic variation; reduce number of haplotypes

molecular clock hypothesis

random neutral genetic mutations are introduced at a constant rate

forces which increase genetic diversity

mutation

forces that increase and decrease genetic diversity

natural selection

mate choice

migration

identity by descent (IBD)

the property that two alleles can be traced back to the same recent ancestor

inbreeding coefficient

probability that two homologous alleles in an individual are identical by descent (IBD)

Fis

Fis

inbreeding coefficient; measures deviation from Hardy-Weinberg within individuals

Hs-Hi/Hs

isolation by distance

physically closer populations are more genetically similar/physically distant populations are less genetically similar

prezygotic barriers

habitat/ spatial/ temporal isolation

behavioral

mechanical

genetic difference prevent fertilization

postzygotic barriers

hybrid inviability

hybrid sterility

2nd generation breakdown

sex linkage

the trait/gene/ allele found on the sex chromosome (X or Y) causes unique inheritance

regular linkage

the trait is associated with another trait more often than chance, because they are closer together on the same chromosome

linkage

tendency of genes or DNA sequences located close together on the same chromosome to be inherited together during cell division (meiosis)

haplotype

physical grouping of genomic variants that tend to be inherited together, reflects a unique combination of variants that reside near each other

linkage disequilibrium

alleles at different loci are nonrandomly associated meaning sepcific allele combinations occur more or less frequently than expected by chance

causes: mutation, selection, nonrandom mating, gene flow

P(AB)=P(A)=P(B) total dependance

linkage equilibrium

the allele at one locus tells you nothing about the allele at another locus, haplotype frequencies equal the product of their individual allele frequencies

P(AB)=P(A)*P(B) total indepence

D-statistic

coefficient of linkage disequilibrium

D=P(AB)-P(A)*P(B)

autosomal recessive

non sex linked trait, inherits two copies of a mutated gene one from each parent

autosomal dominant

non sex linked trait, inherits a single copy of a mutated gene

X-linked

genes located on the X chromosome

Y-linked

genes located on the Y chromosome

inbreeding

related parents, multiple paths where you can inherit the same allele (IBD), less observed heterozygosity

outbreeding

unrelated parents, no loops in the family tree, more observed heterozygosity

Ne

effective population size

number of breeding males + number of breeding females

u

mutation rate

molecular diversity

Θ

expected neutral diversity

Θ= 4Ne* μ

Fst

fixation index; measures differentiation among subpopulations

Ht-Hs/Ht

Hs

expected heterozygosity within subpopulations

Hi

observed populations within individuals

Ht

expected heterozygosity in the total population

Fis=0

random mating

Fis>0

deficit heterozygotes

Fis<0

excess of heterozygotes

Fis=1

complete inbreeding

importance of population structure

conservation biology

human genetics

disease spread

agriculture

antibiotic resistent bacteria evolving differently in different places

population structure forms

colonists in new habitats

geographic barrier block gene flow

recent habitat fragmentation

drift

different habitats & selection pressures lead to accumulation differences over time

genetic linkage between genes

when genes and alleles associate with each other more frequently than by chance

happens if they are physically close together on a chromosome so it is hard for recombination to separate them