AP Biology – Ch. 23 – The Evolution of Populations The smallest unit of evolution? Microevolution 3 main mechanisms responsible for change in allele frequency Which one of these consistently improves the match between organisms and their environment?

Microevolution

Microevolution

Microevolution

Microevolution

Five Fingers of Evolution https://www.youtube.com/watch?feature=player_embedded&v=5NdMnlt2keE

23.1 How do the variations that are the raw material for evolutionary change arise? Mutation and sexual reproduction

Genetic Variation

A) Variation Within a Population Discrete or quantitative Either-or-basis vs on a continuum Single gene vs two or more genes

Measuring Genetic Variation Gene variability vs nucleotide variability Average heterozygosity – gel electrophoresis, restriction fragment analysis Nucleotide variability – compare DNA sequences Why is this information important?

Variation between populations Geographic variation-differences in the genetic composition of separate populations Ex) mice populations separated by a mountain range, mummichog fish and a cold-adaptive allele(cline)

Mutation The ultimate source of new alleles Change in the nucleotide sequence of an organism’s DNA Point mutation Alter gene number or sequence

Mutation rates – low in plants and animals even lower in prokaryotes and viruses(but shorter generation time) RNA viruses – mutations accumulate faster – how does this impact treatment?

Sexual Reproduction variation results from the unique combination of alleles that each individual receives due to: - crossing over - independent assortment - fertilization

23.2 – Hardy-Weinberg -population -gene pool/fixed allele -conditions for HW equilibrium? 1. no mutations 2. random mating 3. no natural selection 4. extremely large population 5. no gene flow

23.3 Natural selection, genetic drift, and gene flow – alter allele frequencies directly 1. natural selection – favoring some alleles over others can result in adaptive evolution 2. genetic drift – chance events causing allele frequencies to fluctuate a. founder effect – Ex) Tristan da Cunha b. bottleneck effect – a severe drop in population size due to a change in the environment - case study – prairie chickens

Genetic drift: A Summary significant in small populations can cause allele frequencies to change at random can lead to loss of genetic variation within populations can cause harmful alleles to become fixed

Gene Flow the transfer of alleles into or out of a population due to movement of fertile individuals or gametes serves to reduce genetic differences between populations Fig. 23.12 – Agrotis tenuis – What if?

Modes of selection http://wps.pearsoncustom.com/wps/media/objects/3014/3087289/Web_Tutorials/17_A02.swf

Sexual Selection A form of natural selection in which individuals with certain inherited characteristics are more likely than other individuals to obtain mates http://evolution.berkeley.edu/evosite/evo101/IIIE3Sexualselection.shtml http://www.pbs.org/wgbh/evolution/library/01/6/l_016_09.html

The Preservation of Genetic Variation 1. Diploidy 2. Balancing Selection a. Heterozygote Advantage b. Frequency-dependent selection 3. Neutral Variation

Frequency-Dependent Selection Situation 1 – Butterfly mimics poisonous butterfly Situation 2 - Poisonous butterfly has several morphs Situation 1 – The fitness of the mimics is positively/negatively frequency-dependent – The fitness of a genotype increases as it becomes more/less frequent. Situation 2 – The fitness of each morph is positively/negatively frequency-dependent – Each morph gets fitter as it becomes more/less common. +