ENVS 212 - Midterm 1

Does evolution always go towards complexity?

No

Historical constraint

Evolution cannot make things from scratch- can only work on step before it, so constraints on variability

Locus

Position on a chromosome

Synonymous codons

Different codons that specify the same amino acid

Nonsynonymous Codons

Codons that encode different amino acids

Alleles

Alternate forms of a gene

Single nucleotide polymorphism (SNP)

A single DNA base that differentiates two alleles at a locus

Exons

Segments of a gene that code for a protein

Introns

Segments of a gene between exons that aren’t coding

Are introns or exons more likely to be neutral? Why?

Introns, because they aren’t coded

Function of introns

Known to impact gene expression

Evolutionary change only works if phenotypes are _____

Heritable

Are phenotype and genotype linked? Why?

They are not necessarily linked, because phenotype can be influenced by enviroment

Segregation

The seperation of alleles during meiosis so that each gamete only carries one allele for each locus

Each allele has an equal or disequal chance of being inherited in the next generation?

Equal

Hardy-Weinburg Equilibrium

Characterization of distribution of genotype frequencies in a population that is not evolving

HWE is an example of ______ hypothesis

null

HWE: When ____ is the only factor for genotype frequencies; equilibrium is reached

Segregation

What are the 5 conditions of HWE?

1. Mating is random

2. Population is large (infinite)

3. Gene flow does not occur

4. Mutations do not occur

5. There is no selection on the specific locus (no fitness difference)

If HWE is unrealistic, why do we find evidence for it in nature?

Because mating is random with respect to most loci in the genome

If a population has genotype frequencies at a locus of AA= 0.20, Aa= 0.36, and aa= 0.44, then how would you find allele frequencies?

A = 0.20 + 0.36/2 = 0.38. a = 0.44 + 0.36/2 = 0.62. Check if p + q= 1. Put into equation

Law of independent assortment

A gamete receiving one gene doesn’t influence an allele it gets from another gene

What are the 2 ways recombination can occur?

Independent assortment or crossing over

Crossing Over

When homologous chromosomes swap segments of DNA

Recombination Rate

The chance of recombination occuring between two loci

Recombination rate for loci on the SAME chromosome

r = 1/2

Recombination rate for loci on DIFFERENT chromosome

r < 1/2

Linkage Disequilbrium

Alleles of different loci are found together more often than you’d expect

Linkage diseqilbrium is more likely to occur if the recombination rate is (high or low)

Low

Loci that are closer together experience ____ recombination and _____ linkage

less, higher

Epistasis

When the effect of an allele at one locus depends on the allele at a second locus

Selections will promote linkage when ____

Two alleles have linkage disequilibrium because specfic combinations have higher

Horizontal gene transfer

The movement of DNA between individuals without sexual reproduction

Antibiotic resistance in bacteria is a result of _____ gene transfer

Horizontal

What is the ultimate source of variation in all organisms?

Mutation

Point mutation

A single nucleotide base is changed (Synonymous, nonsynonymous, stop codon)

4 types of structural mutations

Insertions/deletions, inversion, fusion/fission, whole genome amplification

Pseudogene

Nonfunctional gene in the genome

Deletion mutation

A DNA segment is removed

Duplication mutation

A segment of DNA is duplicated and inserted into the

genome

Inversion mutation

When chromosome segment is reversed

Fission mutation

One chromosome breaks into two

Fusion mutation

Two chromosomes becomes one

Fission/Fusion alter the _____ of chromosomes in the genome

Number

How does whole genome duplication happen?

When a gamete is a diploid and is fertilized

Every 10^ what DNA base is a mutat?

10^8

Fitness

The number of offspring an organism produces

Beneficial Mutations

Increase fitness, rare, and acted on by natural selection

Deleterious Mutation

Decrease fitness, more common, selected against

Which is more common - beneficial or deleterious mutations?

Deleterious

Differences between somatic and germ line mutations

Germ line are inherited, and affect whole organism. Somatic line not inherited, only have patch of mutation

Are mutations random?

Yes and No

How are mutations not random

Some mutations are selected against - transitions are more common than transversion but more transversions exist

How are mutations random?

The fitness effects of mutations are random - one isn’t going to be more likely to get a beneficial mutation

Epigenetics

Study of changes in the expression of genes transcription/translation

Example of non-genetic inheritance

Methylation and histone modification of DNA can prevent genes from being expressed

Can methylation and histone modification be inherited?

Yes

How did selective breeding/agriculture change human civilization?

It allowed them to settle in communities and abandon nomadic lifestyle

Quantitative traits

Traits that show continuous variation and can be affected by several to thousands of loci

Quantitative Genetics

Study of how quantitative traits are inherited and evolved

Examples of quantitative traits

Height, weight, skin color, blood pressure

Genotypic Variation

The variation of the discrete 4 nucleotides G,T,A,C

How do traits go from dicrete genotype to continuous phenotype?

Thousands of genes can affect manhy traits, and enviroment can have an influence on traits

When there are more loci, the phenotype becomes ____

Smoother

What can cause evolutionary change without mutations?

Evolution of allele frequencies - little to more loci

What are the 3 modes of selection on quantitative traits?

Stabilizing, directional, and disruptive

Directional Selection

Favors change in the main of the trait

Stabilizing Selection

Favors individuals near the mean of the trait of a population

Disruptive Selection

Favors the largest and smallest traits of a population

Correlation Selection

Selection favors combination of traits (both striped and versatile, or both striped and tall)

Selection gradient

Favors the strength of directional selection on a quantitative trait

What 2 traits are selection gradient based on?

Measure the trait and the fitness

Relative Fitness

Individual fitness/ mean fitness of all individuals

What part of the graph of fitness/trait is the selection gradient found?

The slope of the regression line (Beta)

If B of the regression line is positive that means

The directional selection favors the increase in the mean of the trait

If B of the regression line is 0, then that means

There is no directional selection acting on the trait

Breeder’s Equation

change in z = z- z' = h^2 x S

If h² is 0 then:

Parents and offspring have 0 heritability

If h² is 1 then:

Parent and offspring are identical

Selection Differential (S)

The difference between the mean phenotype of the selected parents and the mean phenotype of the original population

Which variance is the only one that contributes to evolutionary change?

Additive genetic variance

Dominance Genetic Variance (VD)

Where heterozygotes are not intermediate forms of genes

Epistatic interactions (VI)

Effect of one allele on presence of other allele

Is drift stronger or weaker in smaller populations?

It is stronger

Drift causes variation to be lost- true or false

True- moves away from a 50/50 allele frequency

Drift causes populations to differentiate true or false

True

Which kind of selection decreases phenotypic variance in a population?

Stabilizing Selection

What causes linkage disequilibrium?

The two loci of interest are situation close together on the same chromosome

Gene flow between two populations increases genetic differentiation between them - true or false?

False

Genetic drift increase genetic diversity - true or flase?

False

Natural selection acts on groups of individuals and generally favors traits that benefit the population - true or false?

False - acts on individuals, not groups

The effects of genetic drift are greatest when the effective population size (Ne) is very large

False - greatest when smaller population

If heritable alleles are discrete, why is there variation in the phenotype>

Enviromental influences

Is genetic drift unbiased or biased?

Unbiased

Does drift cause variation to be gained or lost?

Lost - loses variation of 50/50

As time goes on, genetic drift causes populations to become ____

fixed

As the population goes up, the time to reach population fixation increases or decreases?

Increases - it takes longer and more generations to reach population fixation

Coalescence

When the lineages of 2 genes converge together

Coalescence involves _____

genetic drift

Effective population size (Ne) measures the strength of _____

Genetic drift