Biology January 23Rd Lecture

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-gen

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that which produces

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hetero-

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different

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inter-

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between/amoung

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intra-

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within; internal

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mono

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one/single/alone

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morph-

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form

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poly-

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many

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Population genetics

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study of genes and genotypes in a population

helps us understand how genetic variation is related to phenotypic variation

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Genotype vs Phenotype?

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genotype- set of alleles that determines (in part) the expression of a particular trait

phenotype- physical (or biochemical) expression of a trait based on genes & environment (Ex. BB or Bb)

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Gene pool

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all of the alleles for every gene in a given population

--- emphasis often on variation in alleles in a population

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Population

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Group of same species that occupy the same environment and can interbreed

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allele frequency calculation

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= # of copies of a specific allele at a specific locus in a population / total # of alleles for that gene in a population

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Genotype frequency calculation

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=# of individuals with a particular genotype in a pop/total # of individuals in a pop

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is the denominator for genotype or allele calculation larger??

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allele- two letters in each, genotype is representative for the entire thing, so twice as many alleles as there are genotypes

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Hardy-Weinburg equilibrium conditions

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-no new mutations

-no natural selection

-pop is so large that allele frequencies do not change

-no migration occurs between different pops

-random mating, aka PANMIXES

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Panmixes

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-random mating (does not change the allele frequency)

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What does it mean if Hardy-weinburg is not at equilibrium?

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-evolutionary mechanism is at work!!

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Hardy-Weinburg Equation? (a gene with two alleles)

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(p + q)^2 = 1, or

p^2 + 2pq + q^2 = 1

p^2 = genotypic frequency of RR

2pq= genotypic frequency of Rr

q^2= genotypic frequency of rr

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Microevolution

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-changes in a population's gene pool from generation to generation

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Why does micro cause change?

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-it introduces new genetic variation (mutations, gene duplication, exon shuffling, horizontal gene transfer)

-evolutionary mechanisms that alter the prevalence of an allele or genotype (natural selection, random genetic drift, migration, non random mating)

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which shows more potential for alter genetic info more? new genetic variation (mutations, gene duplication, etc.), or altering of the prevalence of an allele/geno? (natural selection, random drift, etc)

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evolutionary mechanisms that alter the prevalence of an allele or genotype

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is q recessive or dominant?

is p recessive or dominant?

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Q is recessive, P is dominant

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what happens if the p/q change over time?

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HW Equilibrium is not reached, evolution is happening

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Five mechanisms that can cause MICRO evolutionary change?

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-mutations

-natural selection

-genetic drift

-migration

-non-random mating

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Natural selection

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-process in which beneficial traits that are heritable become common in further generations

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over time, natural selection results in

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adaptations because of allele changes (promotes survival & reproduction for the population in that environment)

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Reproduction success

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-likelihood of an individual contributing fertile offspring to the generation

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What two traits must an organism have to have reproductive success?

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-must have good reproduction/offspring

-can survive and adapt

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Do allele variations caused from random mutation cause natural selection?

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NO

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Modern description of natural selection

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-some alleles encode proteins that enhance survival or reproductive capability, which are more likely to survive and give their alleles to the gene pool of the next generation

-over the course of many generations, allele frequencies may change through natural selection, therefore altering the characteristics of the population

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Dawrinian Fitness?

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-likelihood that a genotype will be passed on the gene pool later; measure of reproductive success, not JUST physical

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The more dominant and common an allele...

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-the more likely it will be passed on, and the higher the reproductive ability

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-so what does it mean if a male has lots of babies?

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he is very fit in terms of Darwinian Fitness, but it also depends on the health of babies and if the babies were naturally conceived

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Mean fitness of population

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-average reproductive success of members of a population

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Should mean fitness increase or decrease over time?

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-should increase if environment can support extra offspring (can be competition between populations)

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Natural selection patterns (4)

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-directional selection

-stabilizing selection

-disruptive/diversifying selection

-balancing selection

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Directional selection

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-individuals at one extreme of a phenotypic range have greater reproductive success in a particular environment (light vs dark fur in a dimly light forest will eventually shift towards darker fur)

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Stabilizing selection

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-favours the survival individuals with intermediate phenotypes

-extreme values of a trait not selected

-narrowing effect

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Example of stabilizing selection

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-clutch size of birds, more and more birds find that happy medium, slow low curve goes into heightened curve with little on either ends

-too few eggs cannot replace parents

-too many eggs not enough food and all of them die

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how else can stabilizing change?

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-directionally due to the amount of resources available

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Disruptive/Diversifying selection

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-favours survival of two or more different genotypes which produce different phenotypes

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where do disruptive systems occur?

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-heterogeneous environments

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can members of the populations in a disruptive/diversified population interbreed?

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YES

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what does the scale look like for a disruptive population?

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two humps, for two different phenotypes, ex. contaminated and non soil, theres some plants that can resist and some that cant

-extremes do well, not intermediates

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Balancing selection

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-maintains genetic diversity

-two or more alleles are kept in balance, therefore maintained in a population over many generations

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what are the two common ways for balancing selection?

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-heterozygote advantage (ex. H^s allele)

-negative frequency-dependent selection (rare individuals have a higher fitness)

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Sexual selection is a form of

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-natural selection

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what does sexual selection promote?

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-reproductive success because individuals are more likely to choose a mate successfully

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does sexual selection affect male or female characteristics more?

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male

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intrasexual selection

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-between members of the same sex

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examples of intrasexual selection in males?

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-horns in male sheep, antlers in male moose

-this results in male-male competition for mating opportunites/territory

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intersexual selection

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-between members of opposite sex

-female choice, can be cryptic

-male impresses female

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how does intersexual selection prevent inbreeding?

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-genital tract/egg selects against genetically related sperm

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negative about intersexual selection?

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-can decrease survival, as bright colors impress females

-in places with less predators, fish will be brighter,

-this makes a balance between sexual selection and escape from predation

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Genetic drift

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-changes in allelic frequency due to random chance (events unrelated to fitness)

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what % of allele frequency does genetic drift favor?

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-0% or 100%; loss or fixation over time

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fast in ________________ populations

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smaller (not as many alleles)

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Bottleneck- subset of ___________________________

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genetic drift

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Bottle neck

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-population reduced dramatically then eventually rebuilds

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why does the population dramatically decrease in bottleneck?

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-no reason, natural problem, not because of adaptations

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since not all genes are in the sample, bottleneck results in

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-less genetic variation in new population, especially in small populations

-example, frogs in pond

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Founder effect

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-small group of larger population separates and starts a new colony

-new colony will have less genetic variation than original population

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Neutral theory

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-non Darwinian; neutral variation

-much of variation is caused by genetic drift; not selected by a particular allele; accumulation of neutral mutation which have come about because of genetic drift (NOT NATURAL SELECTION)

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where does neutral theory occur?

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-third base of codon

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Migration

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-gene flow that occurs when populations migrate, which have different alleles

-between same species though; they can still interbreed

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does migration enhance or take away genetic diversity in the population?

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enhances it

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example of migration?

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-deer on either side of mountain, suddenly has a pass in the middle, they can inter-breed=

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Nonrandom mating

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-conditions of Hardy-Weinberg have not been met if mating is not random

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forms of nonrandom mating (2)

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-assortative/disassortative

-inbreeding

-both can change allele frequency over time

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assortative mating

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-similar phenotypes more likely to mate

-increases proportion of homozygotes

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dissortative mating

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-dissimilar phenotypes more likely to mate

-favours heterozygosity

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Inbreeding

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-choice of mate based on genetic history

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allele frequency in inbreeding?

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-does not favour a particular allele

-increases homozygous (can bring out more recessive alleles this way= disease)

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does inbreeding lower mean fitness? what is this called?

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YES, this is called inbreeding depression, as this lowers reproductive success of the population