Evolution, Speciation, and Population Genetics: Key Concepts and Processes

Why do you think these species

end up looking so similar but are

not that closely related?

Developmental Changes

Comparative Biochemistry

Can compare DNA, RNA, or proteins

More similarity means species are more closely related

What is a population?

a group of individuals of the same species living in the same area at the same time

What is a Species?

One kind of individual organism sharing similar physical

and genetic characteristics

Individuals Do not Evolve - Populations Evolve

1. Evolution does not change individuals

(Individuals do not acquire new genetic traits)

2. Evolution changes a population

3. Evolution is change in frequency of a trait

within a population

Genotype

genetic makeup of an organism

Phenotype

An organism's physical appearance, or visible traits

These phenotypes result from our geneotypes and

how the genes we inherit are actually used.

What do phenotypes result from?

Genotypes and how the genes we inherit are used.

What is one condition that must be met for phenotypes to remain unchanged?

No significant change in the Environment.

What must not occur for phenotypes to remain unchanged?

No new DNA mutations.

How do different trait variations affect survival or reproduction in this context?

They don't affect survival or reproduction.

What must happen regarding population movement for phenotypes to remain unchanged?

No immigration or emigration into or out of the population.

What type of mate selection is required for phenotypes to remain unchanged?

Random mate selection.

What is the required population size for phenotypes to remain unchanged?

VERY large population size.

Microevolutionary Processes

Small-scale changes in trait frequencies

within a population over many successive

generations drive a population away from

genetic equilibrium.

Mechanisms of Evolution

1. Gene flow

2. Natural selection

3. Genetic drift

Gene Flow

Movement of alleles from one population to another; Tends to keep the gene pools of different populations more similar

Natural Selection

A process in which individuals that have certain inherited traits tend to survive and reproduce at higher rates than other individuals because of those traits.

Why Evolve?

Natural Selection only drives

evolution if some variations in traits

(phenotypes) survive and/or

reproduce better than others

Darwin's Theory of Evolution by Natural Selection

A population can change over time when

individuals differ in one or more heritable

traits that are responsible for differences

in the ability to survive and reproduce

What is a result of natural selection that involves a shift in the range of values for a given trait in some direction?

Directional selection

What is the result of natural selection that stabilizes an existing range of values?

Stabilizing selection

What is the result of natural selection that disrupts an existing range of values?

Disruptive selection

Sickle-Cell Trait: Selection by two forces

If you inherit the mutated gene for Sickle-cell from

both parents, it causes sickle-cell disease

• If you have only one copy of the sickle-cell mutation

and one normal gene, you are relatively healthy and it gives you some resistance to Malaria

Genetic Drift: Bottleneck Effect

A change in the allele frequency of a population as a result of chance events rather than natural selection.

Sexual Selection

A form of natural selection in which individuals with certain inherited characteristics are more likely than other individuals to obtain mates.

Measured in the number of live, healthy offspring produced

Male Reproductive Strategy

Produce millions of sperm and deliver them to the female reproductive system

Female Reproductive Strategy

compete for high-quality resources to support their offsprings 

- higher rank = better resources, and have more births per year

How does mating lead to evolution?

Parenting Behaviour: Enhancing the survival of offspring can increase parents' reproductive success

Inbreeding

Continued breeding of individuals with similar characteristics

Theory of Indirect Selection

Behaviour that has a genetic component can be indirectly selected for, and even some non-genetic behaviour can have evolutionary effects

Reproductive Isolation

Speciation is the attainment of reproductive isolation

Reproductive isolation arises as a by-product of genetic change

What keeps species separate?

Mechanisms that maintain Reproductive Isolation

Prezygotic isolation & Postzygotic isolation

Zygote

fertilized egg

Prezygotic Mechanisms

prevent formation of the zygote completely due to Ecological, mechanical, sperm dies before fertilization, behaviour and temporal isolation

Postzygotic Mechanisms

1. Embryo Dies (Zygotic Mortality)

2. Born but is feeble (Hybrid Inviability)

3. Hybrid sterility (can not reproduce)

Mechanisms of Speciation: How reproductive isolation is achieved

1. Allopatric speciation

2. Sympatric speciation

3. Parapatric speciation

4. Speciation by Polyploidy

Allopatric Speciation

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

What happens to species separated by geographic barriers?

They will diverge genetically.

What can extensive genetic divergence prevent?

It can prevent interbreeding even if the geographic barrier later disappears.

Sympatric speciation

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

Parapatric speciation

speciation occurring when two populations have continuous distributions and some phenotypes in that distribution are more favorable than others

Why would these two different species remain separate if can they hybridize?

Speciation by Polyploidy

Speciation by Polyploidy

new species formed when chromosome number in hybrids doubles, allowing polyploid hybrids to mate with other polyploid hybrids, but not with either parent species; thus, creating a new hybrid species that is reproductively isolated from either parent species

Patterns of Speciation

Gradual Model, Punctuation Model and Adaptive Radiation

What is adaptive radiation?

A burst of divergence

What does adaptive radiation involve?

A single lineage gives rise to many new species

What do new species do in adaptive radiation?

Fill vacant niches