POPULATION GENETICS Chapter 23 1 Quick Review Natural

POPULATION GENETICS Chapter 23. 1

Quick Review Natural Selection Organisms better suited to the environment SURVIVE & REPRODUCE at a greater rate than those less suited to the environment and this is how… SPECIES EVOLVE

Quick Review Natural Selection Variation Natural Selection Speciation

Evolution Starts with Genetics Mutation Variation Natural Selection Speciation

Variation in Gene Pools Collection of alleles within a population Phenotypes: white, brown, gray Genotypes: WW, Ww, ww

Hardy & Weinberg We can study changes in phenotypes in a population over time We can calculate allele frequencies based upon the genotypes We can convert phenotypes into genotypes Thus, a math equation will show if evolution is occurring

Ex: Allele Frequencies in Snapdragons Collect data of phenotypes of a population � 320 red flowers, 160 pink flowers, & 20 white flowers Convert phenotypes to genotypes � 320 RR � 160 RW � 20 WW Calculate allele frequencies �R alleles = 320 + 160 � W alleles = 20 + 160

Ex: Allele Frequencies in Snapdragons Hypothetically 500 flowers � RR-red (320) � RW-pink � WW-white (160) (20) Allele Frequency � 800 / 1000 R alleles exist (80% or 0. 8) � 200 / 1000 W alleles exist (20% or 0. 2)

Ex: Allele Frequencies in Snapdragons Hardy-Weinberg: � If evolution is not occurring in this population � Then allele frequency will remain constant over time Therefore at any moment the population will have: � 80% R alleles � 20% W alleles If 10 years later: � 50% R alleles � 50 % W alleles � Then microevolution is occurring

Applying H. W. E. This happens to nearly all populations for all traits p represents the dominant allele (R) q represents the recessive allele (W) p+q=1 0. 8 R alleles + 0. 2 W alleles = 1

Solve this story problem In certain Native American groups, albinism due to a homozygous recessive condition. If the frequency of the allele for this condition is 0. 06, what is the frequency of the dominant allele in this population? p+q=1 P +. 06 = 1 p =. 94

Extrapolating H. W. E. Equation 1: � p + q = 1 (shows allele frequencies, but not genotype frequencies) H. W. E. Equation 2: (1) X (1) = 1 � (p + q) X (p + q) = 1 � p 2 +2 pq + q 2 = 1 � 500 Snapdragon Ex: p =. 8 & q =. 2 � (. 8)2 +2(. 8*. 2) + (. 2)2 = 1 �. 64 +. 32 +. 04 = 1 � 320 + 160 + 20 = 500 �

Applying H. W. E. p 2 = homozygous dominant condition 2 pq = Heterozygous condition q 2 = homozygous recessive condition p 2 +2 pq + q 2 = 1 RR + 2 RW + WW = 1

Solve this story problem In a certain flock of sheep, 4 percent of the population has black wool If black wool is a recessive trait, what percentage of the population is heterozygous for this trait? p +q = 1 p 2 +2 pq + q 2 = 1

H. W. E. Conditions When would allele frequencies not change over time?

H. W. E. Conditions � Very No large population size isolated disasters impacting allele frequencies � Isolation No � No immigration/emigration (gene flow) Mutations No new genotypes/phenotypes � Random No � No from other populations Mating picky females choosing one allele over another natural selection No environmental pressures selecting one allele over another

1. Mutations/Recombination Rarely impact plants and animals � ~1/100, 000 genes � 98% of our DNA is junk (noncoding) � Somatic cell mutations die with animal Only Gamete mutations are inherited

1. Mutations/Recombination Once a mutation occurs, nearly all phenotypic variations will result from shuffling of existing alleles

2. Genetic Drift Changes in the gene pool of a population � Typical Effect: decrease in genetic variation � The smaller the population, the greater the effect

2. Genetic Drift: Bottleneck effect Small population survives a disaster

2. Genetic Drift: Founder effect Small population is responsible for colonization

3. Gene Flow Individuals from different populations interbreed � Result of immigration/emigration

4. Natural Selection Promotes favorable traits Disposes unfavorable traits

4. Natural Selection: Environment Changes in the biosphere, select better suited alleles

4. Natural Selection: Sexual selection Individuals choose mates based on particular traits

Summary: Microevolution Changes that affect the gene pool of a population Mutation Variation Natural Selection Speciation