Biodiversity chapter 17

What are the mechanisms of evolution

What are the mechanisms of evolution

• natural selection

• mutation

• migration

• drift

is non random mating a mechanism of evolution

no it is not

What is a population?

a group of organisms that includes all of the individuals of a single species that live together in the same place and time

what is microevolution

how populations change over time because of changes in how common specific gene variants (alleles) are within the population.

What is phenotypic variation?

heritable variation in appearance and/or function

what is phenotypic plasticity?

expression of a different phenotype with the same genotype

What is quantitative variation? what is an example?

individuals differ in small incremental ways. ex. lengh

what is qualitative variation? what is an example?

characters with discrete state. ex colour

What is polymorphisms

discrete variants of a character (phenotypic definition but there is a genotypic version)

what is a high narrow curve with little variation among individuals suggest?

that selection of some sort is probably occurring

what is a broad low curve with a lot of variation among individuals suggest?

that selection may not be strong because no phenotypes are “winning”

What may impact phenotype variation?

genetics, environment, or an interaction of the two

what is the difference between genetics vs environment affecting the phenotype?

genetics are heritable and will be passed down

how can you determine if phenotypes are due to genes or environment

experiments such as: keeping genetics constant but changing the environment or breeding experiments (Mendels)

if there is alot of phenotypic variation then the cause is probably ________

environmental

if there is not alot of phenotypic variation the cause is probably ______

genetic

The Hardy-Weinberg principal is a null hypothesis that defines:

a population that is not evolving

What is evolution redefined

a change in allele frequencies from one generation to the next, changing how common a particular allele is within a population (frequency) changing the genetic make up of a population

populations often contain substantial ______ variation

genetic

what is population genetics

studying the genetic variation that exists in a population and how the genetic variation changes over time due to evolution

why does genetic variation occur?

because individuals contain different versions of the same genes (different individuals may carry different alleles for one or more genes) and as they reproduce the offspring gets some of those genes resulting in variations

What is a locus?

location of a gene on a chromosome

what is a gene pool?

all alleles at all loci in a population

What is polymorphism?

a difference in the nucleotide sequence of a given gene in different individuals of a species. the gene occurs in different “forms” in the population (ex. the gene has different alleles in the population)

What does SNP stand for? what is an examples

single nucleotide differences. ex looking at an individual with a disease and looking at the SNPs to associate with certain diseases

What are the two potential sources of genetic variation?

• production of new alleles

• rearrangement of existing alleles into new combinations

What can cause production of new alleles?

• mutations

• migrations

What is genotype frequency?

percentages of individuals possessing a genotype (genotypes have to add up to 100%)

what is allele frequency? how is it calculated?

How common dominant allele is or recessive allele is. calculated from genotype in diploid organisms. p and q are two different alleles at a locus

What are null models?

conceptual models that serve as theoretical reference points to observations

what is the hardy-weinburg principle?

conditions where diploid organisms have genetic equilibrium (no evolution, static)

What conditions must be met for population to be in Hardy-Weinberg equillibrium?

• no mutations occurring

• populations closed to migration

• population infinite in size

• all genotypes free of selection

• random mating with respect to genotype (only condition measured over 2 generations)

What are the fundamental conclusion of Hardy-Weinberg equilibrium

1. allele frequencies in a population will not change generation after generation

2. if allele frequencies in a population are given by pq then the genotypic frequencies will be given by P², 2pq, q²

Why do biologists use HW equilibrium?

• proof no evolution has occurred

• provides null model (but you need to take sampling issues into account)

• HW rest on several key assumptions (deviation means you look back to try to find out which of the four mechanisms is causing evolution)

• if violated HW conclusions may not hold

What does it mean if it is assumed there is no natural selection?

• all individuals survive at equal rates

• individuals contribute equal number of gametes to the gene pool

what happens if the assumption no natural selection is violated?

some individuals with some genotypes survive and reproduced better than others, allele frequencies will change

What does it mean if it is assumed there is no mutation?

• no copies of existing alleles were converted by mutation into copies of other existing alleles

• no new alleles were/are created

• small effect, only important long term

what happens if the assumption no mutation is violated

some alleles have higher mutation rates than others, allele frequencies will change

What does it mean if it is assumed there is no migration?

• no individuals move into or out of the population

• assume isolated population with no gene flow

what happens if the assumption no migration is violated?

individuals carrying some alleles move out of the population at higher rates than individuals carring other alleles, allele frequencies will change

what are the two types of migration

emmigration (leaving)

immigration (coming)

What does it mean if it is assumed there is no chance events?

nothing happens that causes individuals with some genotypes to pass more of their alleles to the next generation than others (no blind luck) and is avoided if the population is infinitely large (no bottle neck)

what happens if the assumption no chance events is violated

genetic drift, allele frequencies will change from one generation to the next

What does it mean if it is assumed individuals choose their mates at random?

gametes find each other randomly

what happens if the assumption individuals choose their mates at random is violated

individuals will prefer to mate with other individuals with the same phenotype (F0), during F1 no change will happen to the allele frequencies but during F2 the genotypic frequencies may change (due to inbreeding)

true or false the eggs dont screen against inbreeding

false, the eggs screen against inbreeding and seek the sperm least likely to result in inbreeding

true or false HW identifies what conditions cause evolution

true

what are the four agents of microevolution

1. gene flow

2. genetic drift

3. mutation

4. natural selection

gene flow

introduces new alleles into populations, may occur from individuals or gametes (plant sperm or birds). life history/behavour may enhance gene flow (behaviours of migrations or something else).

genetic drift

reduces genetic variability within populations, most important in smaller populations and reduces genetic variability NON SELECTIVE MECHANISM. doesn’t lead to adaption but does change allele frequencies

mutations

random and create genetic novelty. only two things make it matter, small populations and long periods of time

natural selection

shapes genetic variability by favouring some traits over others

what can enhance gene flow? example?

dispersal agents. ex bluejays moving seeds around

What is migration

movement of alleles between populations, not the same as seasonal movements of individuals, a form of gene flow. varies depending on mobility of individuals with propagules

what should frequencies be under HW?

A1A1=0.64, A1A2=0.32, A2A2= 0,04

true or false after migration a single bout of random mating will put the population back to HW

true

population bottleneck

reduction in alleles due to population reduction. loss of genetic diversity, some alleles totally gone, only common make through the rare are usually lost completely

founder effect

allele frequencies likely different from the older large population due to chance (very important in conservation biology)

is genetic drift a selective mechanism?

no it is a non-selective mechanism

is genetic drift random?

yes

does genetic drift impact large populations?

only unless it is over many many generations otherwise it only effects small populations

what is sampling error?

random discrepancy between theoretical expectations and actual results

sampling error +evolution=

founder effect

What was the founder effect prediction for silvereye birds?

birds on different islands have different allele frequencies so everytime they jump from on island to another allele variation gets smaller and smaller.

What is mutation?

change to double strand sequence of DNA, spontaneous or caused by other facts. deleterious mutations are harmful to organism

what are the types of mutations

• point mutation

• insertion

• deletion

• inversion

• duplication

point mutation (substitution)

a single nucleotide (base) is changed

insertion

one or more nucleotide base pairs are introduced into a DNA sequence

deletion

one or more nucleotide base pairs are removed from a DNA sequence

inversion

a segment of DNA breaks and is inserted back into its original position in the reverse orientation

duplication

DNA is copied twice; the duplication can be part of a gene, a whole gene, or an entire genome

what are the different modes of selection?

• directional selection (most common)

• stabilizing selection (semi common)

• disruptive selection (relatively rare)

what is directional selection

favors individuals near one end of the phenotypic spectrum

what is stabilizing selection?

favors individuals with intermediate phenotypes (favors average value)

what is disruptive selection

favors individuals with extreme phenotypes (bimodal peak disruptive selection)

inbreeding reduced _______

heterozygosity

what effect does inbreeding have on the percentege of heterozygotes and homozygotes

the % of heterozygotes will decline by 50% each generation, whereas homozygotes will increase 25% each generation, however from one generation to the next allele frequency does not change

does the deviation in HW equilibrium from inbreeding mean evolution is occuring?

no because allele frequencies do not change from generation to generation, it simply affects how genotypes are packaged into diploid zygotes

true or false inbreeding changes proportion of alleles in a population

false it simply moves them from heterozygote to homozygote genotypes

what is inbreeding depression

decrease in the average fitness of inbred individuals. deleterious alleles tend to be “unmasked” more in an inbred population more homozygous recessive) which is typically harmful or even lethal

what can resolve inbreeding depression

outbreeding (genetic rescue)

inbreeding depression=

loss of fitness

what is purging

something being wiped out

interbreeding coefficient leads to loss in _____

fitness

true or false animals and plants have evolved mechanisms to avoid inbreeding?

true, eggs actively seek sperm that is least likely to cause inbreeding and mate choice is genetically controlled (example with the smells)

when is inbreeding unavoidable?

some small populations, common for rare or endangered species and captive breeding problems

what is hybridization

mating between individuals of two genetically distinct populations (can be between species, or the same species)

interspecific hybridization

hybridization between species

intraspecific hybridization

hybridization within a species

hybrid sink

situation where immigration of locally unfit genotypes produces hybrids with low fitness that reduces local abundance

Hybrid vigour (heterosis)

hybrid offspring have higher offspring than either of the parents (or parental organisms)

what poses threats to biodiversity

environmental change, invasive species, overharvesting, habitat loss

genetic rescue

“aggressive” effort to conserve decline population by using hybridization (either very good or very bad)

outbreeding depression

loss of fitness due to parents genetic differences

how does genetic rescue reduce extinction risk

by increasing absolute fitness, increasing population size or growth rate often owing to immigration of new alleles

fitness of individuals of a given phenotype indicated via relation between distribution of ____ (abundance) and _____ (broken line)

phenotypes, fitness function

What does this graph represent?

small at risk population with reduced phenotypic and genetic variation that could benefit from genetic rescue

What does this graph represent

successful genetic rescue with an increase in fitness following prescribed gene flow

How do you perform genetic rescue and why do you perform it that way?

you bring in few key individuals with different alleles because too many would cause outbreeding depression, low levels of immigration should be enough to decrease frequency of deleterious alleles and provide genetic variation