BIOL 3010 Exam III

polygenic

their expression is influenced by many genetic loci and may depend on nonadditive interactions between alleles at these loci aka epistasis

quantitative genetics

continuous phenotypic traits, a difference of degree

variance

the dispersion of a trait

meaning of Vp = Vg + Ve

total variance is the sum of genetic differences and environmental conditions that give rise to differences

broad sense heritability (H2) proportion equation

Vg/Vp or Vg/Vg+Ve

broad sense heritability

looks at what is attributable to genetic variance but the con is that genetic variance is represented as a single value rather than smaller components

what is the problem with H2

not all genotype is transmitted to offsprings bc some effects are lost. the comination of alleles change during meiosis so only some genetic variation actually contributes to the phenotypic resemblance bw offspring and parents

H2 includes what that h2 doesnt

dominance and epistasis

what is epistasis

the expression of a of gene is altered by the expression of other 1+ genes

what effects gets transmitted from parent to offspring and are in h2

additive effects

how are dominance and epistatic effects transmitted

results from interactions among other alleles. this depends on what it is paired with

what population benefits from narrow sense heritability measures the most

evolutionary responses to selection in diploid, sexual populations

when are interactions among alleles transmitted to generations

bacteria (no meiosis)

asexual organisms

inbred populations

• we can use H2 to predict these populations better

Vg = Va + Vd + Vi

genetic variance = additive, dominance, and epistatic interactions

what is the ratio for h2

h2 = Va/Vp

directional selection

favors individuals on one end

stabilizing selection

favors the middle

disruptive selection

favors the tail ends

selection is not synonymous with evolution

it can potentially lead to it though

selection differential S

the strength of the phenotypic selection based on the difference between mean phenotype of individuals (Xb) and mean phenotype of parents (Xp)

h2 = 0

if differences depend solely on the environment, no evolving

h2 = 1

if differences are only because of genetics, offsprings look like parents, evolution response will look like the strength of selection

R = h2 X S

evolutionary response = transmittable phenotypic variance (heritability) X phenotypic variation influencing fitness (strength of the selection)

linkage equilibrium

the occurrence of an allele at one of the two loci is independent of the presence/absence of an allele at the other locus

linkage disequilibrium

the occurrence of an allele at one loci is non-randomly associated with the placement of the other allele at the other locus

recombination divides loci that are

further away from each other

• in other words close loci have less of a chance of being divided bc there is less DNA separating them

physical linkage

the adjacency of two+ loci on the same chromosome

super genes

a group of functionally related genes located close together that they segregate as a single unit

what mechanism allows alleles for loci on different chromosomes to be inherited independently from each other (linkage equilibrium)

independent assortment

what mechanism makes alleles at loci also assort independently if far enough appart

genetic recombination

close loci = low recombination = ?

linkage disequilibrium

quantitative trait locus

DNA correlated with variation in a phenotypic trait. These regions have/are linked to genes that contribute to population differences in a phenotype

• markers that have associations with the expression of a phenotypic trait

genome-wide association mapping

scanning through genomes of many individuals to search for markers associated with the expression of the trait of interest

• best for humans or other widely studied organisms that have a good gene map

QTL vs GWA

QTL = crossing individuals from divergent populations

GWA = large sample size in a single population, grouped on phenotype, and compared

phenotypic plasticity

the capacity for a genotype to express more than one phenotype depending on the environment

reaction norm

the pattern of phenotypic expression of a single genotype across environments. these depict how development maps the genotype into the phenotype as a function of the environment

If Vp exists but plants are all identical then

Vp = Ve

broad sense vs narrow

broad = heritability is the genetic component

narrow = heritability is the results of additive effects of alleles

the rate of adaptive evolution depens on

1. strength of selection

2. heritability of traits

what evolves from phenotypically plastic traits

reaction norms rather than the trait themselves

difference bw selection differential and evolutionary response

evolution = changes on allele frequency

why dont dominance and epistasis contribute to resemblance

these effects depend on the genotype

parthenogenesis

female sex cells undergo meiosis but are not fertilized by sperm. females produce only daughters

hermaphrodites

both male and female organs present

the twofold cost of sex

asexual multiplies faster

sexual males cannot produce offsprings which halves the rate of replication

sex disadvantages

twofold cost

search cost

reduced relatedness

STIs

advantages of sex

combining good mutations

new genotypes

faster evolution

clearance of deleterious mutations

muller’s ratchet

bad mutations accumulating in asexuals irreversibly

genetic load

the burden imposed by the accumulation of deleterious mutations

the red queen effect

to maintain relative fitness, each population must constantly adapt to the other

• evolutionary arms race between hosts and parasites

• explains the importance of sex

process of sex

1. meiosis halves chromosome count

2. fertilization restores chromosome count and makes a zygote

ansiogamy

sexual reproduction involving the fusion of two dissimiliar gamtes: larger egg and smaller sperm

fecundity

reproductive capacity of an individual (number and quality of eggs/sperm)

certainty of paternity

the probability that a male is the father of the offspring from his mate

• therefore females are more likely to give more care to the offspring

operational sex ratio

ratio of male to female individuals who are mature to mate

two types of sexual selection

1. intrasexual

2. intersexual

intrasexual selection

members of the more abundant group competes for the limiting group

intersexual selection

limiting sex discriminates among mate choices from the other sex

sexual dimorphism

the difference in form between males and females of a species

direct benefits

food, nest sites, protection (affects the female directly)

indirect benefits

enhance the quality of the offspring

sexual selection affects what sex

the one with the greater variance in reproductive success (usually males)

positive feedback of female preference and sexual trait

coevolution of stronger preferences and larger display traits

traits can originally be arbitrary but then

females cna choose based based on high quality characteristics

costly signals are the most reliable because

they are difficult for those of poor genetic quality

phylogenetic species concept

species are the smallest possible groups whose members are descended from a common ancestor and who all possess defining characteistics that are distinguishable

biological species concept

species are groups of interbreeding natural populations that are reproductively isolated

meta populations

group of spatially separated populations of the same species that interact at some level

general lineage species concept

species are metapopulations of organisms that exchange alleles frequenty that they constitute the same gene pool and have the same evolutionary lineage

isolating barrieres

environment. genetic, behavior, physiology, ecology that reduces gene flow

• geographic or reproductive barriers

allopatric speciation

geographic separation

reproductive isolation

reproductive barriers prevent reproduction

• timing

• pollination

• courtship rituals

• zygote formation/gametic incompatibilities

• pre and post zygotic viability

sympatry

same geographic area

bateson-dobzhansky-muller incompatibilites

genetic incompatibilities from epistatic interactions

allopatric population diverge why

independent mutations, selection, and drift. then they cannot interbreed even when the barrier is gone

magic trait

a trait that also confers ecological divergence and reproductive isolation

what things can generatre new species rapidly in plants

interspecific hybridization and allopolyploidy

hybridization can do what

erode genetic differences and occasionally produces new species that is reproductively isolation from the parent species

cryptic species

lineages that historically have been treated as one species because they are morphologically similar but are later revealed to be distinct

parapatric speciation

a smaller population usually at the periphery is isolated but there is overlap in the middle

order of events for allopatric speciation

geographic separation → genetic divergence → reproductive isolation

allopolyploidy

occurs in plants and animals

doubles chromosomes as a results of hybridization

quick speciation

merging of two branches

biogeography

explores geopgraphy and history to explain distributions of species in space and time

what explains the distribution patterns of taxa

dispersal and vicariance

dispersal

taxon crosses a preexisting barrier (like an ocean)

vicariance

when a barrier interrupts the preexisting range of the taxon, preventing gene flow between the now separated populations

mutualism

pos pos

commensalism

pos neu

host-parasite relationship

generates negative frequency-dependent selection, reciprocal interation that maintains their genetic variations

cheaters

mutualistic interactions are vulnerable to these invaders, collapsing the mutualism or the evolution of defenses

coevolution makes species highly dependent on each other

if one species becomes extinct the other is more likely to disappear too

mitochondria and plastids are endosymbiotic bacteria

they coevolved with their hosts until they became organelles

retroviruses

endogenous retrovirsues and mobile genetic elements coevolved with their host genomes

antagonistic

pos neg

examples of populations in arms race

parasite-host and predator-prey

introgression

the movement of alleles from one species to another

• certain genes are favored by natural selection after they were introduced to a species thru hybridization

humans are

primates (morphology and DNA confirms)

primates originated when

at the end of the cretaceous period

when did hominins diverge from other apes

8 million years ago

bipedalism and upright statue evolved when

in hominins while they were still small-brained