Evolution of species, genes, and genomes

Challenges of Species Concepts

Can't be typological

There is no one definition

species concepts

Morphologically coherent groups

Genetic similarity clusters

Groups of ecologically exchangeable individual

Biological Species Concept

Separate species are reproductively isolated from one another

Pre-mating pre-zygotic barriers

Habitat isolation

Temporal isolation - don't mate at same times

Behavioral isolation - reject mating behavior

Post-mating pre-zygotic barriers

mechanical isolation - genitals don't match

gametic isolation - gametes are not compatible(receptors)

post-mating post-zygotic barriers

reduced hybrid viability - F1 doesn't develop fully

reduced hybrid fertility - F1 is sterile

Hybrid breakdown - F2 is messed up

Problems with BSC

Fossils

Ring Species

Ring species

species 1 can mate w/ species 2

species 2 can mate w/ species 3

species 3 can't mate w/ species 1

allopatric speciation

The formation of new species in populations that are geographically isolated from one another.

sympatric speciation

The formation of new species in populations that live in the same geographic area

Allopatry

can passively happen by vicariance events

Actively by dispersal events

vicariance event

any event which results in the separation of one geographic range into two.

dispersal events

members of a species cross an existing barrier and establish a new population

Dobzhansky-Muller incompatibility

independent mutations at interacting epistatic loci in different isolated populations causes incompatibility

Neutral Theory of Molecular Evolution

The hypothesis that most mutations that become fixed are neutral mutations and have become fixed by genetic drift.

Rate of neutral molecular evolution

neutral mutation rate x probability of fixation of neutral mutation

2Nµ

probability that a new mutation reaches 100%

1/(2N)

Rate of neutral molecular evolution combined equation

mutation rate: µ

Implications of Neutral Theory

1. If the mutation rate is constant, neutral evolution should happen at a constant rate

2. If beneficial mutations are very rare, the rate of evolution is a function of the fraction of mutations that are neutral (f0)

molecular clock

sequence distances(rate*time) between species can estimate how long ago their ancestors lived

deleterious mutation

Genetic changes that are harmful to an organism.

beneficial mutation

any change to the genetic code that results in noticeable physiological changes that are of benefit to the organism

neutral mutation

A mutation that has no effect on the organism

Transposons

(jumping genes) short strands of DNA capable of moving from one location to another within a cell's genetic material

Genome organization

genome size and number vary greatly

Sequence conservation

By comparing genomes of different species you can figure out which areas are important based on mutation rate

low constraint

most mutations are neutral, f0 high

high constraints

most mutations are deleterious, f0 low

Mutations from low constraint to high constraint

Synonymous

non-coding DNA

3 types of regulatory non-coding DNA

nonsynonymous