Population genetics and evolution What is evolution?

Population genetics and evolution What is evolution? –Descent with modification

Population genetics and evolution What is evolution? –Descent with modification –A change in the characteristics of a population over time

Population genetics and evolution What is evolution? –Descent with modification –A change in the characteristics of a population over time –A change in the frequency of genes in a population over time

Population genetics and evolution Some genetics terminology –Chromosomes …

Population genetics and evolution

Some genetics terminology –Chromosomes … –Homologous chromosomes …

Population genetics and evolution Some genetics terminology –Chromosomes … –Homologous chromosomes … –Locus …

Population genetics and evolution Some genetics terminology –Chromosomes … –Homologous chromosomes … –Locus … –Alleles …

Population genetics and evolution Some genetics terminology –Alleles may be dominant and recessive

Population genetics and evolution Some genetics terminology –Alleles may be dominant and recessive –In Biston betularia, the gene for melanism is dominant (M)

Population genetics and evolution Some genetics terminology –Alleles may be dominant and recessive –In Biston betularia, the gene for melanism is dominant (M) –The gene for typical color is recessive (m)

Population genetics and evolution Some genetics terminology –Alleles may be dominant and recessive –In Biston betularia, the gene for melanism is dominant (M) –The gene for typical color is recessive (m) –Each individual moth has two alleles: –MM and Mm are melanic, mm are typical

Population genetics and evolution Gene frequencies –The frequency of all of the alleles at a particular locus in a population = 100% or 1.0

Population genetics and evolution Gene frequencies –The frequency of all of the alleles at a particular locus in a population = 100% or 1.0 –If there are two alleles, the frequency of one = p and the frequency of the other = q

Population genetics and evolution Gene frequencies –The frequency of all of the alleles at a particular locus in a population = 100% or 1.0 –If there are two alleles, the frequency of one = p and the frequency of the other = q –p + q = 1.0

Population genetics and evolution Gene frequencies –The frequency of all of the alleles at a particular locus in a population = 100% or 1.0 –If there are two alleles, the frequency of one = p and the frequency of the other = q –p + q = 1.0 –With sexual reproduction, p + q alleles in the eggs are combined with p + q alleles in the sperm

Population genetics and evolution Gene frequencies –(p + q) x (p + q) = (p + q) 2 = p 2 + 2pq + q 2

Population genetics and evolution Gene frequencies –(p + q) x (p + q) = (p + q) 2 = p 2 + 2pq + q 2 –In Biston betularia: –p 2 = MM, 2pq = 2Mm, q 2 = mm

Population genetics and evolution Gene frequencies –(p + q) x (p + q) = (p + q) 2 = p 2 + 2pq + q 2 –In Biston betularia: –p 2 = MM, 2pq = 2Mm, q 2 = mm –The population is composed of p 2 homozygous melanic individuals, 2pq heterozygous individuals (which are melanic), and q 2 homozygous typical individuals

Population genetics and evolution Gene frequencies –(p + q) x (p + q) = (p + q) 2 = p 2 + 2pq + q 2 –In Biston betularia: –p 2 = MM, 2pq = 2Mm, q 2 = mm –Phenotype frequencies: –Let ’ s say for argument ’ s sake that the population consists of 81% typical individuals and 19% melanic individuals …

Population genetics and evolution Gene frequencies –If p 2 = MM, 2pq = 2Mm, and q 2 = mm –And if q 2 =.81, what is q, the frequency of m?

Population genetics and evolution Gene frequencies –If p 2 = MM, 2pq = 2Mm, and q 2 = mm –And if q 2 =.81, what is q, the frequency of m? –q = 0.9 (0.9 2 = 0.81)

Population genetics and evolution Gene frequencies –If p 2 = MM, 2pq = 2Mm, and q 2 = mm –And if q 2 =.81, what is q, the frequency of m? –q = 0.9 (0.9 2 = 0.81) –What is p, the frequency of M?

Population genetics and evolution Gene frequencies –If p 2 = MM, 2pq = 2Mm, and q 2 = mm –And if q 2 =.81, what is q, the frequency of m? –q = 0.9 (0.9 2 = 0.81) –What is p, the frequency of M? –p = 0.1 (p + q = 1.0)

Population genetics and evolution Gene frequencies –If p 2 = MM, 2pq = 2Mm, and q 2 = mm –And if q 2 =.81, what is q, the frequency of m? –q = 0.9 (0.9 2 = 0.81) –What is p, the frequency of M? –p = 0.1 –p 2 = 0.01 (MM), 2pq = 0.18 (Mm)

Population genetics and evolution Gene frequencies –If p 2 = MM, 2pq = 2Mm, and q 2 = mm –And if q 2 =.81, what is q, the frequency of m? –q = 0.9 (0.9 2 = 0.81) –What is p, the frequency of M? –p = 0.1 –p 2 = 0.01 (MM), 2pq = 0.18 (Mm) –19% of individuals are melanic

Population genetics and evolution To summarize: –Homozygous dominants = MM = p 2 –Heterozygotes = Mm = 2pq –Homozygous recessives = mm = q 2

Population genetics and evolution What happens during reproduction? –Meiosis separates alleles into gametes

Population genetics and evolution What happens during reproduction? –Meiosis separates alleles into gametes –Gametes bear alleles in proportion to their frequency in the population …

Population genetics and evolution What happens during reproduction? –Meiosis separates alleles into gametes –Gametes bear alleles in proportion to their frequency in the population … –there are p sperm with M and q sperm with m

Population genetics and evolution What happens during reproduction? –Meiosis separates alleles into gametes –Gametes bear alleles in proportion to their frequency in the population … –there are p sperm with M and q sperm with m –there are p eggs with M and q eggs with m

Population genetics and evolution What happens during reproduction? –Meiosis separates alleles into gametes –Gametes bear alleles in proportion to their frequency in the population … –there are p sperm with M and q sperm with m –there are p eggs with M and q eggs with m –Eggs and sperm combine to form zygotes …

Population genetics and evolution What happens during reproduction? EGGS SPERMM (p = 0.1)m (q = 0.9) M (p = 0.1)MM (p 2 = 0.01)Mm (pq = 0.09) m (q = 0.9)Mm (pq = 0.09)mm (q 2 = 0.81)

Population genetics and evolution After reproduction: –Homozygous dominants = MM = p 2 = 0.01 –Heterozygotes = Mm = 2pq = 0.18 –Homozygous recessives = mm = q 2 = 0.81 –Melanics = 0.19 ( ) –Typicals = 0.81

Population genetics and evolution After reproduction: –Homozygous dominants = MM = p 2 = 0.01 –Heterozygotes = Mm = 2pq = 0.18 –Homozygous recessives = mm = q 2 = 0.81 –Melanics = 0.19 ( ) –Typicals = 0.81 –THIS IS WHAT WE STARTED WITH!!

Population genetics and evolution What is evolution? A change in gene frequency within a population

Population genetics and evolution What is evolution? A change in gene frequency within a population What processes lead to changes in gene frequency?

Population genetics and evolution processes that lead to changes in gene frequency:

Population genetics and evolution processes that lead to changes in gene frequency: –Mutation (the ultimate source of all genetic variation)

Population genetics and evolution processes that lead to changes in gene frequency: –Mutation –Gene flow (usually accomplished by migration of individuals from one population to another)

Population genetics and evolution

processes that lead to changes in gene frequency: –Mutation –Gene flow –Non-random mating (inbreeding may increase the production of homozygotes with recessive alleles, which may be selected against)

Population genetics and evolution processes that lead to changes in gene frequency: –Mutation –Gene flow –Non-random mating –Selection (the most powerful agent of evolutionary change)

Population genetics and evolution processes that lead to changes in gene frequency: –Mutation –Migration –Non-random mating –Selection –Genetic drift (changes in gene frequency in small populations due to random sampling error)

Population genetics and evolution Genetic drift: –Changes in gene frequency in small populations due to random sampling error

Population genetics and evolution Genetic drift: –Population bottlenecks - reduction of population size results in loss of genetic variation and potentially in the loss of alleles from the population –Reduction of population size must be catastrophic and non-selective

Population genetics and evolution Genetic drift: Population bottleneck

Population genetics and evolution Genetic drift: –The Founder Effect - a small population disperses from a larger population, and founds a new population in another geographic location. The gene frequencies in the founding population are not representative of the larger population. –Especially important in speciation on archipelagoes

Population genetics and evolution