EVE 100 Midterm 1 Study Guide

Why study evolution?

To explain why the natural world is the way it is and to understand our place in the world

What is evolution?

Descent with modification

What are the 5 points of Darwin's theory of evolution?

1) Evolution, 2) Common descent, 3) Gradualism, 4) Population change, 5) Natural selection (P1. Variation, P2. Heritability, P3. Differential success

What are the 3 laws of Mendelian genetics?

1st: Factors (alleles) are separated (or segregated) during formation of gametes

2nd: Separate traits are passed independently of one another from parents to offspring

3rd: Some factors (alleles) exert more effect than others -> dominant and recessive alleles

What is a locus/what are loci?

The basic unit of genetic inheritance. The location of a genetic element (ex nucleotide, gene, etc)

What are alleles?

DNA sequence variants at a locus

What is a genotype?

Genetic constitution of an individual at a particular locus

What is a haplotype?

A set of alleles located in adjacent (linked) loci

What is a phenotype?

Observable physical characteristics expressed in individuals

What is a mutation?

The ultimate source of genetic variation. There are multiple different types that segregate in a population

What is the Hardy-Weinberg theorem?

The idea that a dominant allele would intrinsically increase in a population, and rare alleles would tend to be lost in a population

How does Hardy-Weinberg equilibrium affect genetic variation?

In Hardy-Weinberg equilibrium, genotype frequencies will remain unchanged in all generations after the first generation

What are the assumptions of the Hardy-Weinberg theorem?

Diploid sexual population with discrete generations, equal allele frequencies in both sexes, mendelian segregation of alleles, random mating, NO mutation, NO migration, large population size with NO genetic drift, and NO natural selection

In Hardy-Weinberg equilibrium, what occurs at low allele frequencies?

In particular, with allele frequencies less than 0.1, almost all A1 alleles are contained in heterozygotes, which allows deleterious recessive alleles to be maintained in a population regardless of their negative fitness effects

What are the two different types of homozygous genotypes that result from inbreeding?

They may be non-identical by descent (alloyzgous) or identical by descent (autozygous). Autozygous genotypes MUST be homozygous, whereas allozygous genotypes can be wither homozygous or heterozygous

What is the inbreeding coefficient (F) ?

This is the probability that an individual taken at random from a population will be autozygous (homozygous)

What is the consequence of inbreeding in terms of frequency?

The frequency of homozygotes is higher than the frequency of heterozygotes compared to a population in HW equilibrium. Inbreeding changes genotype frequency

What is an inbreeding depression?

Inbreeding increases the number of homozygotes in a population and exposes more deleterious alleles as homozygotes, reducing fitness.

An inbreeding depression can affect all aspects of reproductive fitness: offspring numbers, juvenile survival, longevity, interbirth

interval, mating ability, gamete quantity and quality.

What are the two most important forces that affect allele frequency in a population?

Genetic drift and Selection both affect allele frequency changes in a population

What is genetic drift?

Fluctuations in allele frequencies that occur by chance, particularly in small populations, because of sampling error. This leads to a loss of genetic diversity over time

What causes genetic drift to occur?

Chance events that cause unpredictable fluctuations in allele frequencies from one generation to the next

What size of population experiences a higher rate of genetic drift?

The rate of genetic drift is higher in small populations. Allele frequencies do drift in very large populations, but at a very slow rate

What is fixation, and what does it result in?,

Ultimate fixation is the inevitable loss of alleles in a population

What is a population bottleneck?

The severe loss in gene diversity from a catastrophic event (high death rate in a population)

Ex: northern elephant seal

What is an effective population size?

The number of individuals in an idealized population that would produce the same amount of genetic drift as in the real population of study. AKA the number of individuals in a population that are reproducing and contributing genetics to the next generation

What factors affect effective population size?

-Variation in the number of progeny among males, females, or both

-Sex ratio departure from 1:1

-Natural selection

-Inbreeding

-MOST IMPORTANTLY fluctuations in population size

How does coalescence time relate to effective population size?

Coalescent times for two alleles is longer in larger populations than it is in smaller populations

In what two ways are mutations random?

1. Although we may predict the probability that a certain types of

mutation occur; we cannot predict which gene copies will undergo

the mutation.

2. The chance that a particular mutation will occur is not influenced by

weather or not the organism is in an environment in which that

mutation would be advantageous.

What is natural selection?

The process of differential reproductive success. Natural Selection exists whenever there is variation in fitness.

What three conditions are needed for evolution by natural selection to proceed?

1) There is phenotypic variation in a population of reproducing individuals

2) Phenotypic traits are heritable

3) Different phenotypes differ in rates of survival and reproduction (differential fitness)

How is an adaptation both a process and a state?

As a process: adaptation describes the portion of evolutionary change in a trait that was driven by natural selection

As a state: an adaptation is described as that aspect of the current condition of a trait that can be reliably ascribed to the past action of natural selection.

What is fitness?

A relative measure of the success of an entity surviving and reproducing, and thus contributing copies of itself to future generations. Two components are viability (survival to reproductive age) and fecundity

How do you calculate absolute fitness?

Absolute fitness is viability x fecundity

How do you calculate relative fitness?

Relative fitness is absolute fitness / highest absolute fitness

What does the coefficient of selection measure?

S measures the selective advantage of the genotype with the highest relative fitness

What is a beneficial mutation?

A mutation that enhances survival or reproductive success

What is a deleterious mutation?

A mutation that lowers the chance of survival and reproduction.

What population size sees a stronger effect of natural selection? Why?

Natural selection is more efficient in larger populations

What is directional selection?

A form of selection that leads to a point of equilibrium where a beneficial allele is fixed

What is the frequency distribution of an advantageous recessive allele in a population?

An advantageous recessive allele takes a long time to increase in frequency because, when at low frequencies, most allele copies are present in heterozygotes- and therefore are invisible to selection

What is the frequency distribution of an advantageous dominant allele in a population?

An advantageous Dominant allele increases in frequency more rapidly because it is expressed in both homozygous and heterozygous genotypes

What is overdominance (aka heterozygote advantage)?

When heterozygote genotypes can have higher fitness than the homozygote genotypes

Can selection lead to evolution?

Selection can potentially lead to evolution if the difference in reproductive success is tied to genetic variation

Continuous distribution of most traits explained by:

1) Most quantitative traits are multifactorial (have more than one locus affecting them)

2) Most traits are affected by the environment

Phenotypic variation within a population is usually...

Phenotypic variation within a population is usually continuous, often has a normal (Gaussian) distribution

What are the two main components of phenotypic variation?

1. Environmental variation such as diet, noise, temperature, or sunlight

2. Genetic variation: the segregation of alleles within the population that influence the phenotype

What is broad sense heritability (H^2)?

The proportion of the total phenotypic variance attributable to genetic differences among individuals

When calculating phenotypic variation, what is Vp?

Vp is the total phenotypic variance in the population

When calculating phenotypic variation, what is Vg?

Vg is variance due to genetic differences

When calculating phenotypic variation, what is Ve?

Ve is variance due to environmental differences

What is narrow sense heritability?

For evolutionary change, we are interested in narrow sense heritability

What is additive genetic variance?

The component of genetic variance that "shows up" next generation. The quantity a (additive effect of an allele) measures how a phenotype is affected by the genotype at this locus. Such additive effects constitute the additive genetic variance (VA).

Additive gene action is aptly named because one can merely add up

the effects of each allele in a genotype to determine the total effect

on the phenotype.

What is dominance in terms of genetic variance?

If allele A1 is dominant, A1A1 and A1A2 genotypes have similar trait

value, but offspring can have different trait values depending on the alleles they receive from parents. So, Dominance lowers the predictability of trait values in offspring.

What are epistatic effects on genetic variance?

The effect of one allele at one locus depends on which allele is

present at a different locus

How does selection act on phenotypic variance?

The response to selection depends on how much of it is due to additive genetic variance

What determines how much a trait evolves?

Selection differential S and heritability h^2. The magnitude of change depends on strength of selection (selection differential) and the narrow sense heritability

What is the Breeder's equation?

R (response time) = S (selection differential) x h^2 (heritability)