Q.Q. 4/3/19 Within which level of biological organization is evolution occurring? Organism Ecosystem Community Population

Chapter 23- Population Genetics

Population Genetics and Evolution Population- Localized group of individuals that are capable of interbreeding and producing fertile offspring

Key Terms: Microevolution- The change in genetic makeup from generation to generation (Individuals are selected, populations EVOLVE!) Modern Synthesis- Integration of many other fields of study into evolution (such as statistics, botany, etc…) Gene Pool – ALL alleles at all loci of a population

Hardy-Weinberg Theorem Frequency of alleles and genotypes in a population gene pool will remain CONSTANT from generation to generation- if ONLY Mendelian segregation and recombination of alleles are at work. It would be a NON-EVOLVING POPULATION! *Equilibrium = stays the same

Hardy- Weinberg Equilibrium- Genotypic frequencies can be predicted using the following formulas:

Hardy-Weinberg Equilibrium IE- 500 wildflowers will have 1000 genes for color CRCR = Red = 320 flowers x 2 =640 CR genes CWCW = White = 20 flowers x 2 40 CW genes CRCW = Pink = 160 flowers x 1= 160 CR genes, 160 x 1 CW genes

Hardy-Weinberg Equilibrium CR = 640 + 160 = 800 CW = 40 + 160 = 200 800/1000 = .8 = 80% = p 200/1000 = .2 = 20% = q Statements that can now be made- - 80% chance that a wildflower will carry CR - 20% chance that a wildflower will carry CW

Determining Genotype frequencies using Hardy- Weinberg Equilibrium: Chance of: CR CR = .8 x .8 = .64 OR CAN BE WRITTEN: p x p = .64 OR CAN BE WRITTEN: p2 = .64 .64 = 64%

Hardy-Weinberg Equilibrium CW CW = .2 x .2 = .04 OR CAN BE WRITTEN: q x q = .04 OR CAN BE WRITTEN: q2 = .04 .04 = 4%

Hardy-Weinberg Equilibrium CWCR = .2 x .8 = .16 OR CAN BE WRITTEN: q x p = .16 = 16% CRCW = .8 x .2 = .16 OR CAN BE WRITTEN: p x q = .16 = 16% *same!

Hardy-Weinberg Equilibrium Overall- p2 + 2pq + q2 = 1 (or 100%)

5 Conditions required for Hardy- Weinberg Equilibrium: 1) Large population size 2) No gene flow between populations (no immigration/emigration of organisms within populations) 3) No mutations 4) Random mating (no selection for certain traits; i.e. coloring, patterns,etc) 5) No natural selection

*Do these conditions TRULY exist in any biological system? NO, but conditions in a stable population are usually very close to these conditions and close enough to use Hardy- Weinberg Equilibrium as a tool to make predictions.

Example Problems: IE- PKU is an inherited disorder that 1 in 10,000 people are born with (homozygous recessive). How many people in a this population would be carriers of PKU? *REMEMBER: recessive = letter q so homozygous recessive = q2   q2 = 1/10,000 = .0001 To determine frequency- √.0001 = .01 = q (or 1% of population will have PKU allele)

p = 1 – q 1- .01 = .99 = p (or 99% of the population will carry the dominant allele) How many are carriers (heterozygous)??

Hardy-Weinberg Equilibrium 2pq = 2 x .99 x .01 = .0198 (or about 2% of the population will be heterozygous)

More H-W Practice Problems Complete the last 2 word problems in your notes!

Changes in Gene Pools Mutations that can cause changes 1- Point Mutations 2- Chromosomal Mutations

Change We can predict mutation rates, but NOT the actual mutation Sexual recombination can cause change in a population

The three factors that alter allele frequency and cause the most evolutionary change are: 1) Natural Selection

2 types of Genetic Drift: The three factors that alter allele frequency and cause the most evolutionary change are: 2) Genetic Drift- Fluctuation in allele frequency based on a finite population size and chance. 2 types of Genetic Drift: Bottleneck Effect- Sudden change in environment reduces size and only several individuals survive. These individuals may not be reflective of the original gene pool.

2nd type of Genetic Drift (continued) Founder Effect- Individuals become isolated from a population and establish a new population.

The three factors that alter allele frequency and cause the most evolutionary change are: 3) Gene Flow- Genetic additions/subtractions from a population resulting in a “movement” of a trait. IE- Pollen from one island flower moves to another island and spreads its genes to that new location. *immigration/emigration

More about natural selection: Genetic variation- Phenotypic polymorphism- two or more distinct morphs represented in highly notable frequencies Average heterozygosity- Average heterozygous loci in a population. IE- 1,920 of 13,700 of a certain loci are heterozygous = 17%

More about natural selection: Geographic variation- Differences in gene pools of separated populations (perhaps separated by a mountain range) Clines- Graduated change in a trait along a geographic axis

Fitness Fitness- The contribution an individual makes to the gene pool of the next generation. - Usually ranges from 0  1 - If an individual has a fitness of “0” they do not pass on any traits (no reproduction) - If an individual has a fitness of “1” the entire next generation is composed entirely of those individuals genes/traits

Selection Selection- 1) Directional Selection- Environmental change or a migration shifts the frequency curve 2) Disruptive Selection- Favors variants and removes intermediates 3) Stabilizing Selection- Removes extreme variants and favors intermediates

Sexual Selection Sexual Selection- Natural selection for mating success Intrasexual- IE- Males fighting males for the right to breed with females Intersexual- Mate choice. Usually female choosing the “best” male

Sexual Reproduction Sexual Reproduction is “inferior” to asexual reproduction. - Asexual individual population will outgrow that of the sexual individuals.