bio midterm number three

what is true about the harvey-weinburg equilibrium

it only applies if the population is in equilibrium, or if no evolution is happening, which is unrealistic, so it acts as a null hypothesis to reject

no change in allele frequencies=harvey weinberg

what are the five H-W assumptions

-no mutations

-no selection against/for phenotypes

-random mating

-infinite population size

-no gene flow

these are the parameters of harvey weinberg that are impossible to realistically emulate, there will always be some sort of selection, mutations, mating preferences. Gene flow is likely and population size is not infinite, as the limitations of population growth

how does diploidy maintain genetic variation if selection should lessen genetic variation, and if selection always happens

diploidy hides recessive alleles in homozygous individuals, so natural selection cannot act on the alleles as they are not present in the phenotype

how does fluctuating selection maintain genetic variation despite the selection paradox

the changing environment selects for different traits at different times, preventing the fixation of a certain allele

how does heterozygote advantage maintain genetic variation?

heterozygotes have a hidden recessive allele, if they have an advantage than the allele that is selected against is still preserved

local environment maintains genetic variation in a species

if a species is present in multiple environments, different alleles are favored and genetic variation is maintained. This is different than fluctuating selection because that sways back and forth with the time of year, while the local environment always selects for the same trait, there is just variation in environment

evolutionary history limits evolution

a trait cant just pop out of nowhere, it needs to evolve from preexisting structures.

trade off limits evolution

you cant have it all, one trait is good for one thing and bad for another, so you cant have a perfect trait that is good for everything-imperfect solutions

what conveys information in a phylogenetic tree?

horizontal branching and branch length, not vertical position

mono, para, and poly phyletic groups

monophyletic groups are groups that include common ancestors and all their descendants, basically one big, all-encompassing clade

parapyletic groups are groups that include common ancestors and some of their descendants, so one, partial clade

polyphyletic groups are groups that do not include a common ancestor, not on the same clade 

plesiomorphy, apomorphy, synapomorphy

plesiomorphy are traits that come from a common ancestor, everything on the clade should share that evolved trait

apomorphy is a derived trait, that evolved later and is different from an ancestor

synapomorphies are shared derived traits, which help identify clades

what are four kinds of evolutionary relationships we can identify from derived traits, and how do they differ in orgin

homologous-shared similar evolutionary orgin, divergent evolution

analogous-evolved independently for the same function, convergent evolution

evolutionary reversal-when a lineage reverts to an ancestral trait, like how whales ancestors started in the ocean, went to land, and then back to the ocean

homoplasy-similar traits that evolve through convergent evolution, those who have these did not get these traits from the same course of evolution (ex. bats and birds)-homoplasy is an umbrella term, so all analogous traits are homoplasies

parsimony principle

there are many possible phylogenetic trees for the same lineages, as they are just hypothesis. The parsimony principle states that whichever one is simplest is the best one

which type of selection moves the mean trait value, which type of selection increases genetic variation

directional selection is the only type of selection that moves the mean trait value, it moves it towards whichever extreme has a higher fitness.

Disruptive selection is the only type of selection that increases genetic variation, as it favors two extremes

stabilizing selection keeps the same mean trait value, and decreases genetic variation

what are the six pieces of evidence used to support evolution

-fossils

-molecular biology

-vestigial structures

-homology

-artificial selection

-direct observation, experimental evidence

describe four evolutionary processes

mutation

they arise randomly at a rate that is low and constant, there are more mutations in larger populations, as about each individual has a couple mutations

geneflow

alleles moving in of a population from another population, migration of individuals, movement of gametes, increases genetic variation

genetic drift

random change in allele frequencies, such as a natural disaster. These have big impacts on small populations, and small impacts on large populations

non-random mating (sexual selection)

choosing mates with specific phenotypes

what are two types of genetic drift? explain them.

bottleneck effect

some sort of event happens and there is a large decrease in population, random loss of genetic diversity

founder effect

occurs when a small group of a population leaves to establish a new population, random sample of that populations alleles

describe the form of binomial nomenclature

a species is named, first with the latin genus, which is followed by the genus name. Sometimes, the person who classified the species’ name is tagged onto the end of the name

what does the length of the branches help us make?

molecular clocks, which use the rates of evolutionary change to help estimate evolutionary time

sequence alignment

by comparing shared dna sequences among related organisms, we can find the small differences, revealing evolutionary change in genes and protiens

more time that species have diverged=more sequence differences

similarity matrix

compares species based on their number of similarities and differences in their sequence alignment

why are the number of changes in similarity matrixes underestimated? explain all the possible reasonings, and draw diagrams

multiple substitution- a dna sequence experiences two mutations, which would only appear as one

coincident substitution-

parallel substitution- when the same mutation happens to the two species at the same time

back substitution-when the dna is mutated, but then mutates back to the original sequence

synonymous vs nonsynonymous mutations

synonymous mutations are silent mutations, they are not expressed in the phenotype and thus natural selection cannot act upon them. nonsynonymous mutations are expressed in the phenotype, often negative, natural selection does act on them. 

rate of nonsynonymous mutations to synonymous mutations

less nonsynonymous mutations than synonymous mutations, stabilizing selection, selects away from a harmful mutation

synonymous mutations equal to synonymous mutations is neutral evolution, mutations can spread or disappear by chance

more nonsynonymous mutations than synonymous mutations, directional selection, favoring this positive mutation

genome size variation

variation reflects differences innoncoding dna, not gene number

sexual recombination

mullers rachet- the new combination of alleles prevent the buildup of deleterious mutations

gene transfer

in bacteria, introduces new genes and functions

gene duplication

extra copies of genes that can evolve new functions, increase gene product, diverge in expression, become pseudogenes or evolve new functions

dobzhansky-muller model

harmless genetic changes within populations can become harmful when combined across populations, slow speciation of two groups until they experience reproduction isolation

polyploidy is the most common mechanism for sympatric speciation

autopolyploidy-occurs from chromosome duplication in a single species

allopolyploidy-chromosomes from two species combine