Final Exam: Lectures 19-26

microevolution

changes in a single gene/allele

macroevolution

formation of a new species/group of related species

Georges Buffon's Ideas

populations of living things change through time

Lamark's Ideas

species change over generations, adapting to new environments

Concepts from Lamark

1. inheritance of acquired characteristics
2. modified traits inherited by offspring

Catastrophism

Earth has been largely shaped by sudden, violent events (may have been worldwide in scope), with the latest one occurring 6,000 years ago (which fit religious teachings)

Georges Currier's Hypothesis

19th century- Catastrophism

Hutton and Lyell Hypothesis

19th century- Uniformitarianism

Uniformitarianism

Changes in Earth are directly caused by recurring events, helped shape Darwin’s view

Thomas Malthus

the population size of humans can increase linearly due to increased land usage & improvements in agriculture, reproductive potential is exponential but not every member reproduces

Alfred Wallace

published similar ideas to Darwin in the Linnean Society of London; Finches all evolved from a single species similar to the Dull-Colored Grassquit Finch from South America

On the Origin of Species (1859)

Charles Darwin-evolution occurs from generation to generation through natural selection and genetic variation

Natural Selection

each generation produces more offspring than will reproduce, and favorable traits are more likely to be passed down to the next generation and become more prevalent

Biogeography

the study of geographic distribution of extinct & living species

Endemic Species

species naturally found only in a particular location

Convergent Evolution

2 species from different lineages independently evolved similar characteristics (because they occupy similar environments)

Analogous Structures (aka Convergent Traits)

a structure from the result of convergent evolution

Homology

a similarity that occurs due to descent from a common ancestor

Homologous Structures

structures similar to each other due to a structure in a common ancestor

Vestigal Structures

anatomical features with little or no current function but resemble structures of presumed ancestors, may be eventually eliminated by natural selection

Molecular Homology

a similarity between organisms at the molecular level- more genetic similarity = more related

Example of Molecular Homology

P53 gene in humans, fish, and birds

Population Genetics

the study of forces that influence the composition of a population’s gene pool; how alleles behave in populations

Population

A group of individuals of the same species that occupy the same environment at the same time and can interbreed

Gene Pool

all of the alleles for every gene in a given population

3 Processes of Sexual Species

Production of Gametes, Unification of Gametes, Production of Phenotypes

Production of Gametes

Ploidy, # of loci, the position of loci, # of alleles/locus, mutation rates, rules of inheritance

Unification of Gametes

System of mating, pop^n size, migration, age structure

Production of Phenotypes

Phenotypes independent of the environment
Genotypes interact with the environment

Hardy-Weinberg Assumptions

1. Diploid, one locus, autosomal, 2 alleles, no mutation, Mendel’s First Law
2. Random mating, infinite pop^n size (removes chance sampling effects), no migration, discrete generations
3. All genotypes have equivalent phenotypes with respect to gamete production (= no selection)

Punnett Squares

Write genotypes of female and male side by side, and assume any frequencies we want for X, Y, Z
- F and M must match
- X + Y + Z = 1
- Mating occurs randomly
- Impose Mendel’s First Law

Hardy Weinberg Equilibrium

Random mating causes no change in allele frequency; as long as assumptions hold:
* no change in genotype frequencies
* no change in allele frequency
*NO EVOLUTION

Nonrandom Mating

Inbreeding, Positive Assortative Mating, Negative Assortative Mating, Walhund Effect

Inbreeding

mating between relatives and affects the whole genome

Positive Assortative Mating

similar phenotypes mate and affects genes involved and linked genes

Negative Assortative Mating

dissimilar phenotypes mate, XY sex determination

Walhund Effect

increased number of homozygotes as a result of population subdivision

Selfing

Deviates from HWE
*half heterozygotes produced from a heterozygote
* 25% dominant, 25% recessive
* eventually weeds out heterozygotes

Consequences of Inbreeding

Large changes in frequencies of rare genotypes, Severe genetic disease (deleterious alleles are more likely homozygotes)

Positive Assortative Mating

Affects only loci controlling the traits and closely linked genes

Negative Assortative Mating

*Affects only loci controlling traits and closely linked genes
-XY and ZW sex determination
-Self-incompatibility alleles in plants
*Generates selection that maintains variation
*Affects allele frequency

Fitness

the average lifetime contribution of individuals of a genotype to the population after one or more generations

Directional Selection

individuals at one extreme of a phenotypic range have greater reproductive success in a particular environment

Stabilizing Selection

favors the survival of individuals with intermediate phenotypes
* extreme values of a trait are selected against

Disruptive Selection

favors the survival at phenotypic extremes
* likely to occur in populations that occupy heterogeneous environments

Polymorphism

many alleles (morphs)

Mutation-Selection Balance

mutation rate to deleterious recessive a alleles = u

Migration-Selection Balance

explains why some populations maintain deleterious alleles

migration

a homogenizing force that reduces population differentiation

Overdominance

produces a stable equilibrium so both alleles are maintained
*Rare allele almost always in favored heterozygote

Underdominance

produces an unstable equilibrium
*Rare allele can’t invade aa or AA populations

Genetic Drift

change in allele frequencies by chance sampling of alleles
*Each generation is a sample of the previous generations alleles
*This sample is subject to sampling errors

Pure Drift

*Changes in allele frequencies each generation are strictly random
*Once an allele is lost it cannot be replaced
*Causes random loss of genetic variation

In drift, a larger population =

weaker drift

Buri’s Experiment Shows...

drift has no direction and causes loss of genetic diversity

Bottleneck Effect

a small number of individuals from a large ancestral population survive

Founder Effect

a small number of individuals from a large ancestral population found a new pop^n

Neutral Theory of Molecular Evolution

*Most mutations are deleterious
*Beneficial mutations are very rare
*Most non-deleterious mutations are selectively neutral
*Mutation → neutral gene pool → Drift
*Mutation keeps pumping new neutral alleles into the population
*Drift keeps removing alleles from population
*Maintains neutral polymorphism

mutation

brings new neutral alleles into population

Drift

causes random changes in allele frequencies

Mutation-Drift Balance

*Drift has no tendency to maintain any particular allele
*Neutral polymorphism is a phase of neutral molecular evolution

Nucleotide substitutions much more likely in _ base of codon

3rd (usually doesn’t change amino acid)

Species

a group of living organisms consisting of similar individuals capable of exchanging genes or interbreeding

Theory of Evolution

explains how populations evolve and how new species emerge

Microevolution

a study of the processes that lead to speciation

speciation

the origin of new species

clonal species

*Genetic exchange (sex) and reproduction are not obligately coupled
*Prokaryotes: genetic exchange is infrequent, fragmentary, and non-reciprocal
*Many Plants: reproduce clonally and sexually
*Many Fungi: reproduce clonally and sexually
*Bdelloid Rotifers: no males, no hermaphrodites, and no meiosis

Bdelloid Rotifers

Diploid, clonal, and no genetic recombination

Transpecific Polymorphisms

arise when the time to coalescence is longer than the time to species divergence

Morphological Species Concept

Species defined by morphology or biochemistry

Evolutionary Lineage Species Concept

Based on sequence data

Paleontological Species Concept

Based on preserved fragments of morphology

Ecological Species Concept

*Species occupy separate ecological niches
*Ignores evolutionary history and reproductive isolation
*Distinct species may have similar niches

Prezygotic Barriers

prevent mating

geographic/habitat isolation

species do not come into contact with each other due to geographic barriers

temporal isolation

reproduce at different times of day/year

behavioral isolation

mating behaviors are incompatible

mechanical isolation

differences in size or genitalia prevent mating

gametic isolation

if interbreeding is attempted, gametes fail to successfully unite

Postzygotic Barriers

prevent production of fertile offspring from mating

hybrid inviability

when a hybrid fertilized egg cannot develop past early embryonic stages

hybrid sterility

an interspecies hybrid may be born viable but it is sterile

hybrid breakdown

hybrids may be fertile, but their offspring are not

Allopatric Speciation

when a gene pool is separated by geography
*Can also occur when a small population moves to a new location that is geographically separated

Adaptive Radiation

single ancestral species evolves into an array of descendants that differ greatly in habitat, form, or behavior

Ring Species

adjacent populations can interbreed but those at geographic extremes cannot

sympatric speciation

when a gene pool is separated by biology
*Polyploidization
*Local adaptation
*less common than allopatric

phylogeny

the relationship between all the organisms on Earth that have descended from a common ancestor, whether they are extinct or extant

distance methods

use % sequence similarity

Cladistic Methods

use shared derived characteristics

Probabilistic Methods

use explicit models of evolution

UPGMA

Unweighted pair-group method with arithmetic means

Maximum Parsimony (cladistics)

Construct a phylogeny using shared derived characters

Ungulate Phylogeny

Phylogenies based on genetic distances (similarities) are very similar to a parsimony tree

Probabilistic Methods search for the best...

*substitution matrix
*rate estimates among sites
*tree topology
*branch lengths

Members of the Hominidae family

gorillas, chimps, humans

humans vs chimps differ by

1.23%

_% of all proteins between humans and chimps are identical

29

many genetic differences in humans and chimps result from...

chromosomal inversions of duplications

Possible Scenario for Human Evolution (which is constantly changing)

*Bipedalism
*Opening of skill moved forward for spinal cord
*Pelvis broadened
*Lower limbs got longer