Evolution Exam 2 Slides

Types of Variation

Types of Variation

Genetic

Environmental

Genotype by Environment Interactions

Phenotypic Plasticity

The ability of one genotype to produce different phenotypes depending on the environment

August Weismann

Germ Plasm Theory

-Germline Vs. somatic cells

-”Weismann barrier”

-Repudiated Neo-Lamarckism

Germ Plasm Theory

Germ cells contain and transmit heritable variation; somatic cells play no role in heredity

Mendels Law of Dominance

“Henceforth in this paper those characters which are transmitted entire, or almost unchanged in the hybridization, and therefore in themselves constitute the characters of the hybrid, are termed the

dominant, and those which become latin in the process recessive.“

Mendels Law of Segregation

“The inheritance of traits is determined by “factors” [genes] that are passed on to descendents unchanged. Alternative versions of genes [alleles] account for the variation in inherited characters.”

Mendels Law of Independent Assortment

Characteristics are inherited independently of each other. Dominant traits can appear in combination either with other dominant traits or with recessive traits.

-Maternal and paternal copies of the genome are scrambled

-Occurs during meiosis in eukaryotes: assortment of homologous chromosomes, recombination

-Exception: linked traits (genes close together on chromosomes less likely to get scrambled so particular alleles can stick together)

William Bateson

Coined the term Genetics, Allelomorphs/Allele, Heterozygote, and Homozygote

Sources of variation in evolution

-Meiosis (crossing over): New combinations of genes.

-Mutation

Who was the 19th-century Austrian monk whose breeding experiments with garden peas revealed fundamental principles of inheritance?

Gregor Mendel

The ability of one genotype to produce different phenotypes in response to environmental conditions is called:

Phenotypic Plasticity

The function that describes how much the phenotype of individuals with a given genotype changes in relation to change in environment (also defined in the textbook as "the pattern of phenotypic expression of a single genotype across a range of environments") is called:

Reaction norm

Briefly explain

(A) the Weismann Barrier

and

(B) how this idea repudiated Neo-Lamarckism.

A) The Weismann Barrier explains somatic cells can be affected by the environment but that does not affect the germline cells. All somatic cells descend from germline cells and are kept separate from each other.

B) This idea repudiated Neo-Lamarckism becuase Neo-Lamarckism state characteristics are acquired through use and inherited by offspring. The Weismann Barrier states that inheritance comes from germline cells and somatic cells cannot alter the genetic information.

Every genetic feature in every organism originated as a _______

mutation

What is a general term for a mutation that creates an additional copy of a stretch of DNA sequence?

Gene duplication

True or False:

Occasionally, a single mutation event -- such as genome duplication -- can "instantly" generate a new species.

True

What is a population?

A group of interacting and potentially interbreeding individuals of a species

Hardy-Weinberg Theorum

-If the allele frequencies in a population are

given by p and q, the genotype frequencies will be given by p^2, 2pq, and q^2

-The allele frequencies in a population will not change, generation after generation

If you are given p and q and calculate p^2, 2pq, and q^2 what have you calculated?

Predicted genotype frequencies

Five critical assumptions of the Hardy-Weinberg Equilibrium

1. No selection

2. No mutation

3. No migration

4. No chance events

5. Random mating

Selection

Differential survival/reproduction of individuals with certain allele(s)

How do we know if observed genotype frequencies are not in Hardy Weinberg Equilibrium?

(X^2) Chi squared statistical test; small differences might be due to sampling error.

X^2= Sum (observed-expected)^2/expected

Mutation-selection balance is the allele frequency at which deleterious alleles are being created by ________

at the same rate they are being eliminated by

________

Mutation, Selection

Insecticide resistance is often conveyed by a single dominant or semi-dominant allele of a particular gene. The alleles are designated “S” for susceptible and “R” for resistant, with possible genotypes of SS, SR, and RR.

Suppose that 100 blowflies of each genotype were treated with pesticide, and the number of survivors was counted. 9 SS blowflies survived, 72 SR blowflies survived, and 90 RR blowflies survived.

A) What are the relative fitness values of each genotype (wSS, wSR, and wRR)?

B) What is the selection coefficient, s, for the SS genotype in the presence of the pesticide?

A)

wSS 0.09/0.90= 0.1

wSR 0.72/0.90= 0.8

wRR 0.90/0.90= 1

B) SS selection coefficient = 0.9. (1-0.1=0.9)

Genetic Drift:

results from chance events that produce different outcomes than we predict

The Founder Effect

Small founding populations are likely by chance to have different allele frequencies than their source populations

True or False:

Genetic Drift is more rapid and dramatic in small populations and can lead to loss of heterozygosity and fixation of alleles.

True

Migration

Movement of alleles between populations (gene flow)

Migration-selection balance

Migration introduces variation that is opposed by natural selection

Why do we care about heterozygosity?

Genetic variation is the raw material for evolution; populations that lack variation cannot respond to environmental change.

Loss of heterozygosity= increase in homozygosity…

Often leads to reduced fitness

(related to inbreeding)

The rate of evolution is…

the rate that new alleles (introduced by mutation) are substituted for other alleles already present.

True or False:

When genetic drift is the only mechanism of evolution at work, the rate of substitution equals the mutation rate.

True

Neutral theory:

Drift dominates and drives rate of evolution

Selectionist theory

advantageous mutations and selection also influence rate

Genetic drift is a __________ mechanism of evolution

nonadaptive

What do VP, VA, VD, and VE represent in the following equation?

VP = VA + VD + VE

VP is the

total phenotypic variation

VA is the

additive genetic variance

VD is the

dominance genetic variation

VE is the

Environmental condition

True or False: If a trait is highly heritable, then differences between populations in that trait must be due to genetic differences between the populations.

False

What is the effect of migration?

-causes populations to become more similar, leads to change in allele frequencies over time

What produces excess of homozygotes (deficiency of heterozygotes)

Inbreeding

True or False:

Since allele frequencies do not change, inbreeding by itself is \n not a mechanism of evolution

True

Quantitative traits:

-Show continuous variation \n -Must be measured

-Ex Height

-Multilocus inheritance

Qualitative traits:

-Come in discrete categories

-Ex Hair color

-Single locus or Multilocus inheritance

Heritability:

The fraction of total phenotypic variation in a trait that is due to genetic variation

Broad-sense heritability

The fraction of total phenotypic variation in a trait that is due to genetic variation

Narrow-Sense Heritability:

The fraction of total phenotypic variation in a trait that is explained by additive genetic variation

-is estimated by comparing traits of parents and offspring and determining the slope. \n

Maximum parsimony

Simplest explanation favored

Bootstrapping

Assigns measures of accuracy to sample estimates

Distance Matrix

Clusters taxa based on genetic distance

Maximum likelihood

Finds most likely tree given specific model of molecular evolution

Bayesian methoda

Looks at probability that a tree us correct given a specific model of molecular evolution

Neutral theory

Most evolution at the molecular level is due to drift

True or false:

Rate of molecular evolution=neutral mutation rate

True

Synonymous (silent) mutation

Does not alter the amino acid sequence of the protein.

(often selectively neutral)

Nonsynonymous mutation

Alters the amino acid sequence of the protein.

(more likely to be subject to selection)

Synonymous substitutions

Do not change protein

Nonsynonymous substitutions

Change protein

Complex adaptations

Coexpressed traits that experience selection for a common, often novel function.

Promiscuous proteins:

Capable of carrying out two functions; are especially likely to take on new functions if duplicated

Paralog:

A homologous gene that arises by gene duplication

Gene recruitment:

The co-option of a particular gene or network for a totally different function as a result of a mutation; the reorganization of a preexisting regulatory network can be a major evolutionary event