Evolutionary Biology Exam 1

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Microevolution

Species change over time

Speciation

Lineages split and diverge

Macroevolution

New life forms derive from older life forms

• Occurs on a huge timescale 

• Uses relative dating

  • Things closer to the surface = more recent

  • Things deeper down = more ancient 

Common Ancestry

All life forms are related

Carbon Dating

• Absolute ages determined by radiometric dating using unstable isotopes of naturally occurring radioactive elements

Using the ratio of C-14 to C-12 can help to estimate time

Evidence for Descent with modification

• We find fossils of species that are not found living today (extinction and macroevolution have occurred)

• Many of these fossils are similar to living forms found in the same geographic area today

• LAW OF SUCCESSION: The correspondence between fossil and living forms in the same local

• e.g. mammalian species differ between continents 

• Evidence of Common Ancestry 

• Homology: The theory of evolution predicts that related organisms will exhibit shared traits (called homologies) because they have a common ancestor (shared ancestry)

Evolution by natural selection requires:

• Variation in the trait

• Trait must be heritable (requires genetic variation) 

• Differential fitness (survival and reproduction)

• Variation in fitness must be correlated with the trait (nonrandom) 

Darwinian fitness:

• the number of offspring (or gene copies) an individual passes into the next generation.

Relative fitness

• an individual’s Darwinian fitness relative to other individuals in the population (typically average fitness is set to one)

• Important principles of natural selection 

• 1. Natural selection acts at the level of individuals, not populations.

• 2. Populations, not individuals, evolve.

• 3. Natural selection is retrospective and cannot predict the future.

• 4. Natural selection is not necessarily progressive.

The five mechanisms of evolutionary change

1. Random Genetic Drift

2. Mutation

3. Selection

4. Nonrandom mating

5. Migration

A useless or rudimentary body part that is thought to have been important in ancestral populations but no longer has a known function

Vestigial Structure

Assumptions of the Hardy-Weinberg Equation

1. No selection

2. No mutation

3. No migration

4. No genetic drift

5. Mating is random

How Mutations Effect Populations:

• Most mutations are deleterious and decrease fitness

• Mutations increase genetic variation

How selection effects populations:

• Selection occurs when some alleles are more like to

  be passed on than others (they increase fitness)

• Purifying: Selection DECREASES genetic variation

• Low fitness alleles tend to be lost, good ones go to fixation

Mutation/Selection Balance

Gene Flow/Migration

• gene flow is simply the movement of genes among populations.

• it can occur by the movement of gametes, or by the movement (and successful breeding) of individuals.

• Gene flow can cause rapid changes in allele frequencies (=evolutionary change)

• The long-term outcome will be the elimination of genetic differences between population sits magnitude is represented by m

• m = the proportion of alleles in a population that have entered from a different population each generation.

Genetic Drift

• Definition: random changes in the frequencies of alleles from generation to generation caused by “accidents of sampling”

• You can think of each generation as “sampling” the alleles of the

  previous generation.

• 
  

Non Random Mating

• A system of reproduction where the probability that two individuals will mate is not equal for all possible pairs in a population.

• Unlike random mating—where every individual has an equal chance of pairing with any other member of the opposite sex, regardless of traits or genetic lineage—non-random mating is driven by specific preferences, physical barriers, or genetic relationships

• Examples: Sexual selection, Geographical/spatial proximity, inbreeding (bad), Assortative mating, Disassortative mating

Selection

The process where specific heritable traits become more or less common in a population over generations because they affect an organism's ability to survive and reproduce

Random genetic drift

• An evolutionary mechanism caused by random, chance fluctuations in the frequency of gene variants (alleles) in a population over time

• Unlike natural selection, drift does not happen because a trait makes an organism "more fit" or better adapted to its environment. It is driven purely by chance and sampling error during reproduction

• Drift has a much stronger effect in small populations, where rare alleles can easily be lost or fixed completely.

• Large populations have a greater buffer against random fluctuations

Effective Population Size:

• Effective population size is not about the ”numbers of individuals” but about the number of “genes contributed” to the next generation

• Official definition: “an ideal theoretical population that would undergo drift at the same rate as the actual population of interest"

Factors that effect effective population size

1. Genetic Bottlenecks: severe (but often short-lived) reductions in effective population size that reduce genetic diversity (I.E Cheetahs)

2. Unequal numbers of (breeding) males and females

3. Large variation among individuals in reproductive success. Reduces effective population size (Ne) because a small number of individuals

Homoplasy/Convergent Evolutions

A broad term for any trait, feature, or DNA sequence shared by different species that was not inherited from a common ancestor.

Point Mutations

a genetic mutation where a single nucleotide base (or a very small base pair) in a DNA or RNA sequence is changed, inserted, or deleted

Gene duplication

A genomic mutation that produces one or more extra copies of a region of DNA containing a gene.

Gene Deletion

A type of mutation that involves the loss of one or more nucleotides, a whole gene, or a larger chromosomal segment from the DNA

chromosomal mutation

a large-scale change that alters the physical structure or the total number of chromosomes in a cell, affecting many genes at once

Frameshift Mutation

A mutation where all downstream codons are affected

Assortative Mating

Individuals prefer to mate with partners who share similar phenotypic traits or genotypes (e.g., tall people mating with tall people). This increases the frequency of homozygotes (individuals with two identical alleles) in the population

Disassortative Mating

Individuals prefer to mate with partners who are phenotypically or genetically dissimilar. This increases genetic diversity and the frequency of heterozygotes (individuals with two different alleles)

Official evolution definition

• Changes in gene or genotype frequencies over time 

Decent with Modification examples

• Species change over time (microevolution)

• Lineages split and diverge (speciation)

• New life-forms derive from older life forms (macroevolution)

• All life forms are related (common ancestry)

• Earth and life is old 

Synapomorphy

A shared trait that was modified (changed from an older ancestral state) in the most recent common ancestor

Clade/monophlyetic group

A group that contains an ancestor and all of its descendants

Outgroup

A group that contains an ancestor and some, but not all, of its descendants

Synapomorphy

A shared trait that was modified (changed from an older ancestral state) in the most recent common ancestor