What Darwin Never Knew

How Genetics influences Evolutionary Thought

Video Clip

● Variation

● Darwin got right

● Darwin's idea has stood the test of time

● Recombination & Mutation

● Natural selection

Sources of Variation

● Mutation

– Asexual or sexual reproducing organisms

– Can be beneficial, negative or neutral depending on environmental conditions the organism finds itself

● Recombination

– Gene shuffling through sexual reproduction

– This provides MOST of the heritable differences between generations

– In humans: 8.4 million different combinations of genes w/ 23 chromosomes

Evolution in terms of Genetics

● Species = individuals that can interbreed with viable offspring

● Share a common group of genes = gene pool

● Gene pool = all genes, all different alleles that are present in a population

● Relative frequency = number of times that allele occurs in a gene pool

● Usually a percentage

● NOTHING TO DO WITH DOMINANCE

Evolution in Genetic Terms

● Evolution = ANY change in relative frequency of alleles in a population

Traits

● Single gene =

● controlled by a single gene (two alleles)

● Remember that most genes have more than two options, so still a lot of variability

● Polygeneic =

● controlled by two or more genes (four or more alleles)

● Many possible genotypes

Traits

Single Gene

● Natural selection on a single gene can lead to changes in allele frequencies –> industrial melanism

Polygenic

● Effects of natural selection are more complex, affect the DISTRIBUTION of phenotypes

Selective Pressure

● Recall that selection causes some traits to survive and spread, while others are lost

● A selective pressure determines which traits are successful

Types of Selection

● Selection pressures

Human Activity as Selective Pressure

● Human activity provides some of the strongest selection pressure in the world today

● Examples:

– Antibiotic Use & Resistance

– Habitat Destruction

– Over Hunting

Genetic Drift & Gene Flow

● Natural Selection is NOT the only source of change

● Alleles can become more or less common by chance

● Remember that genetics is a game of chance & probability

● Smaller populations are more affected by this (smaller gene pool)

● Genetic drift

● Factors affecting the gene pool

Random Changes in Genetic Drift

● Founder Effect

– When a new population is formed from a subset of a larger one, there will be changes in allele frequency

– See example slide.

● The founder effect

Random Changes in Genetic Drift

● Bottleneck Effect

– Occurs when a large, genetically diverse population is drastically reduced by a catastrophic, non-selective event.

– Genetic diversity of survivors is likely to be much lower than that of the original population, even as a population reestablishes itself this low diversity is maintained

– Cheetahs

Speciation

● Natural selection CAN change the relative frequencies of alleles

● Can lead to speciation = changes in a species' gene pool that can create a reproductive isolation between the groups; creating a separate species

Types of Speciation

● Behavioral Isolation

– 2 populations can interbreed but have differences in courtship or other reproductive strategies

Types of Speciation

● Geographic Isolation

– 2 populations are separated by geographic barriers● Mountains, rives, etc.

Types of Speciation

● Temporal Isolation

– 2 populations reproduce at different times

Types of Evolution

● Microevolution

– Any change in allele frequency over a long period of time

● Macroevolution

– Large scale evolutionary pattern or process change over a longer period of time

Patterns of Macroevolution

● Divergent Evolution

● Convergent Evolution

● Coevolution

Patterns: Divergent Evolution

● Two or more related species become more and more dissimilar

Patterns: Convergent Evolution

● Unrelated species become more and more similar as they become adapted to similar environments

● Recall analogous structures

Patterns: Coevolution

● 2 species evolve in response to changes in each other over time

– Insects & flowering Plants

– Mammals & Flowering Plants

– Predator & Prey – CLIP

– Parasites & Hosts