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 – CLIPCLIP – Parasites & Hosts