Evolution Exam 2

Polymorphism

Simultaneous occurrence of two or more alleles within a population

Can result in variation

Polyphenism

A trait for which multiple, discrete phenotypes can arise from a single genotype depending on environmental circumstances

Population genetics

The study of distribution of allele within populations and the mechanisms that cause allele frequency to change over time

Population

Group of interacting individuals and potentially interbreeding individuals of a species

Populations are made up of individuals that carry ___

Alleles

Populations genetics arose from __ __

Modern synthesis

What is modern synthesis

Reconciled Darwin’s ideas of evolution with Mendelian genetics

Also recognized other mechanisms of evolution- gene flow, mutation, and drift

New definition of evolutions

Any change in the allele frequency in a population from one generation to the next

Modern synthesis also helped recognize other mechanisms of evolution such as

1. Genetic flow

2. genetic drift

3. Mutation

What does Hardy-Weinberg principle state

In the absence of outside forces, allele frequencies of a population will not change from one generation to the next and no evolution will occur

Assumptions of Hardy-weinberg equilibrium

1. Population is infinitely large

2. Genotypes do not differ in fitness

3. There is no mutation

4. Mating is random

5. There is no migration

When do allele frequencies change

When the assumptions of HW are violated

When the HW assumption “the population is infinitely large” is violated what occurs?

Genetic drift

Random sampling error causes

Genetic drift

Genetic drift occurs when

A random and non-representative sample of the population produces the next generation

Principles of genetic drift

1. Causes populations that are at first identical to become different

2. Drift is unbiased, allele frequencies are equally likely to go up or down

3. Genetic drift causes variation to be lost

4. Evolution can occur without natural selection

What populations are immune to the effects of random genetic drift?

Only infinitely large populations

Genetic bottleneck

An event in which the number of individuals in a population is drastically decreased

How does genetic drift relate to a genetic bottleneck?

Drift can have a powerful impact on small populations but can also affect populations that are only temporarily small

Probability of fixation formula

X/2N

X= number of copies of an allele in the population

2N= total number of alleles in a population

N= number of individuals in a population

Founder effect

The loss of alleles variations in new populations founded from a very small number of individuals

What event(s) can cause a random set of rare alleles to rise to a high frequency?

Genetic drift and/or founder effects

Fitness

The success of an organism at surviving and reproducing to contribute to the next generation

Components of fitness

1. viability- survival to reproductive age

2. mating success- acquiring mates and successful fertilizations

3. fecundity- number of viable offspring produced

What is inbreeding depression

Decrease in fitness due to inbreeding

Natural selection occurs when individuals vary in ___

Fitness

Positive selection

When one allele leads to higher fitness than another and natural selection favors its spread throughout the population

Components of fitness

1. Survival to reproductive age

2. Mating success

3. Fecundity- number of offspring produced

Fitness is determined by an organisms___

Phenotype

= G + E

How do population geneticists use fitness to understand the change in allele frequency at a single loci?

Measure variation in the expression of a particular trait for fitness of many individuals in a population

Absolute fitness

The raw measure of the average fitness of a genotype

Relative fitness

Fitness of a genotype standardized by comparison to other genotypes

Selection coefficient

Measure the difference in relative fitness between genotypes

What is the difference between population genetics and quantitative genetics

Population genetics studies how allele frequencies change while quantitative genetics studies how phenotypic distribution changes in populations

Selection differential

Describes the difference between the mean phenotypes of reproductively successful individuals and the entire population

Positive selection

When one alleles confers higher fitness than another natural selection will favor its spread throughout the population

Negative/purifying selection

Selection that removes deleterious mutations from a population

Balancing selection

Selection that favors more than one allele

Directional selection

Favors individuals at one end of phenotypic distribution

Stabilizing selection

Favors individuals in the middle of phenotypic distribution

Disruptive selection

Favors individuals at both tails of phenotypic distribution

What is a gene tree

Representation of how copies of a gene descended from a common ancestral allele

Tips of a gene tree represent

Gene copies from individuals

Branches of gene trees represent

Lineages of a gene copy

Nodes of a gene tree represent

Coalescence of gene copies

H-W equation(s)

p² + 2pq + q²

p+q=1

Breeders equation

R= h² + S

Variance equation

V(p) = V(g) + V(e)

Genetic variation is broken down into

V(a)- variation due to additive effects

V(d)- variation due to dominance effects

V(i)- Variation due to epistatic effects

Narrow sense heritability

Proportion of genetic variation due to additive effects

h²= V(a)/V(p)

Broad sense heritability

Proportion of genetic variation due to all genetic differences among individuals

H²= V(g)/V(p)

Molecular homoplasy is (more/less) common that morphological homoplasy. Why?

More common

Uses less characters so there is a higher probability of similarities

Coalescence

The merging of two gene lineages into a single ancestral lineage moving backwards in time

Incomplete lineage sorting

History of a gene differs from the history of the species carrying it

Occurs because ancestors of living species can contain more than one allele

Two methods of developing molecular phylogenies

Maximum Parsimony and distance matrix method

Maximum parsimony

Statistical method for reconstructing phylogenies that identifies the tree that minimizes the total amount of change required to fit data into the tree

Distance matrix methods of developing molecular phylogenies

Procedures for constructing by clustering taxa based on the distance between their DNA or protein sequences

Key characteristics of quantitative traits

They are variable and heritable

Quantitative trait loci mapping

Method for finding regions of genome that influence variation in quantitative traits

Goal is to find associations between specific loci and variation in trait

Genome wide association mapping (GWAS)

Scanning through genomes of many individuals, with and without trait of interest, to search for marker associated with trait expression

Phenotypic plasticity

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

G x E interactions

What 3 reasons has natural selection not removed all deleterious alleles from a population

1. Some diseases occur after reproduction

2. Recessive alleles - carries that don’t know

3. Mutation constantly occurs