Population Genetics and Speciation Chapter 16 Population Genetics and Speciation Mrs. Stewart Honors Biology Central Magnet School

Bell Work List the evidence (at least 3) that supports the theory of evolution.

Standard / Objective CLE 3210.5.3 Explain how genetic variation in a population and changing environmental conditions are associated with adaptation and the emergence of new species.

Variation of Traits Within a Population Variations in the genotypes of a population arise by: mutation – changes in genes that occur either naturally or influenced by environment Passed to offspring if occurs in gametes Recombination – reshuffling of alleles (chromosomes) and crossing over during meiosis random pairing of gametes – organisms produce large numbers of gametes, so the union of a particular pair is strictly by chance.

The Gene Pool The total genetic information available in a population is called the gene pool.

Allele Frequency Allele frequency is the number of times an allele occurs in the gene pool This is in comparison to how often the other alleles occur too

Relative Allele Frequencies determined by dividing the total number of a certain allele by the total number of alleles of all types in the population Expressed as a percentage or a decimal.

Example: I do B = Black b = brown What are the allele frequencies? Total = 50 B = 20/50 = .40 or 40% b = 30/50 = .60 or 60%

Example: We do .60 .40 B = black b = white 12 How many B? _________ What is the allele frequency of B? What is the allele frequency of b? .60 12 How many B? _________ How many b? _________ Total # of alleles for fur color? _________________ .40 8 20

Example: You do Half of the population of four o’clocks has red flowers, and half has white flowers. What is the frequency of “r” allele?

Predicting Phenotype Phenotype frequency is equal to the number of individuals with a particular phenotype divided by the total number of individuals in the population.

Phenotype Frequency

Evolution is any change in the relative frequency of alleles in a population. Populations, not individual organisms, can evolve over time.

Hardy Weinberg Genetic Equilibrium Due to sexual reproduction, phenotypic frequencies may change over time. Does that mean the allele frequencies change too? Unless acted upon by an outside force (perhaps a changing environment), the answer is no.

The Hardy-Weinberg Genetic Equilibrium Allele frequencies in the gene pool do not change unless acted upon by certain forces. Hardy-Weinberg genetic equilibrium is a theoretical model of a population in which no evolution occurs and the gene pool of the population is stable.

What factors affect the allele frequencies in a gene pool? Factors to keep H.W. equilibrium: Lack of mutations No immigration or emigration Ideally large population size Individuals mate randomly Selection does not occur

Calculating using the Hardy Weinberg equation Dominant allele frequency = p Recessive allele frequency = q p + q = 1 p2 +2pq+ q2 = 1

Exit Ticket M.socrative.com Room: stewart348 Final question: How does immigration or emigration affect allele frequencies in a gene pool?

Darwin’s Finches http://people.rit.edu/rhrsbi/GalapagosPages/Pictures/LandBirds/FinchTypes.jpeg

http://www.biology-online.org/images/darwin_finches.jpg

Five conditions under which evolution may take place Genetic mutations Gene flow Genetic drift Nonrandom mating Natural selection.

Mutation Mutations are changes in the DNA.

Gene Flow Emigration and immigration cause gene flow between populations and can thus affect gene frequencies.

Genetic Drift Genetic drift is a change in allele frequencies due to random events. Genetic drift operates most strongly in small populations.

Nonrandom Mating Mating is nonrandom whenever individuals may choose partners. Sexual selection occurs when certain traits increase an individual’s success at mating. Sexual selection explains the development of traits that improve reproductive success but that may harm the individual.

Natural Selection Three general patterns Stabilizing Selection favors the formation of average traits. Disruptive Selection favors extreme traits rather than average traits. Directional Selection favors the formation of more-extreme traits.

The Concept of Species Biological species concept a species is a population of organisms that can successfully interbreed but cannot breed with other groups

Isolation and Speciation Geographic Isolation Results from the separation of population subgroups by geographic barriers. Allopatric Speciation Speciation due to separation of subgroups of a population Reproductive Isolation Results from the separation of population subgroups by barriers to successful breeding. Sympatric Speciation Reproductive isolation within the same geographic area

Allopatry vs Sympatry http://deltabiology.com/wp-content/uploads/2012/02/Sympatry.jpg http://scienceblogs.com/evolvingthoughts/allopatry.jpg

Reproductive isolation: Monkeyflower http://faculty.washington.edu/toby/images/mim29%20Nature.jpg

Reproductive isolation http://evolution.berkeley.edu/evolibrary/images/evo/drosophila_scene7.gif

Rates of Speciation Gradualism Punctuated equilibrium species undergo small changes at a constant rate. Punctuated equilibrium new species arise abruptly, differ greatly from their ancestors, and then change little over long periods.