Genetic variation and Change in populations Population Genetics Genetic variation and Change in populations Population: All Organisms in a geographic area that are the same species and capable of interbreeding. Genetic Variation: allele frequency changes over time Exchange of genetic Material

Allele Frequency how often that allele form appears in a population (as a decimal) Reminder! Allele is a form of a gene Each individual has 2 alleles for each gene so… .5 = 50%, .62=62%, etc… # of individuals = # of total alleles 2 OR… # of alleles = # of individuals x 2

p + q = 1 P = frequency of the dominant allele Q = Frequency of the recessive allele In kermitfrogs the frequency of the dominant allele for being green is .84 (84%). What is the frequency of the recessive allele?

Hardy-Weinberg Equation: P2 + 2pq + q2 = 1 This equation tells you the frequency of genotypes in the population P2 = Homozygous dominant genotype 2pq = heterozygous genotype Q2 = homozygous recessive genotype * P2 or 2PQ =Dominant Phenotype * Q2 = Recessive phenotype

Hardy-Weinberg equilibrium Allele Frequency in non-changing populations Must have all Five conditions 1. no natural selection 2. Completely random mating 3. no mutations 4. Large population size 5. no migration (in or out of the population) When a population is not evolving the allele frequencies are not changing= genetic equilibrium.

Examples- yes, you should have these in your notes  A population of rabbits may be brown or white (the recessive phenotype). Brown rabbits have the genotype BB or heterozygous. White rabbits are homozygous recessive. The frequency of the homozygous recessive genotype is .35. What is the frequency of the recessive allele? What is the frequency of the dominant allele? What is the frequency of heterozygous rabbits?

Moths Example In a population of peppered moths, 30% of the population shows the recessive phenotype of white. Which of the variables does 30% represent? Given this information, what is the frequency of recessive alleles in the population (q)? What is the value of p? How do you know? If this population had 1000 moths. How many moths would be Homozygous dominant? Heterozygous? Homozygous recessive?

Rh protein example In the US, 27% of the population has Rh negative blood, which is a recessive trait. If the student population of lincoln High School was 2,000, how many students would you expect for each of the three possible genotypes? Find q first.

Video: Sickle Cell Disease Answer the 3 questions on the board in your notes

Evolution: Change of allele frequency in a population over time Studying how allele frequencies change in a population over time= studying how the population is evolving Non- hardy Weinberg : 5 causes of evolution *Begins by change in allele frequency* 1. Small populations 2. non-random mating 3. mutation occurs 4. migration (new genes in or loss of genetic diversity) 5. natural selection acts on population

1. Small population size = genetic drift Genetic drift: Elimination or drastic change in allele frequencies due to small population size Random events that eliminate genes from a Small population

Bottleneck Effect When a populations size is dramatically reduced for at least one full generation leaving small population of survivors chosen by chance, NOT genetic fitness to survive Examples: Human Caused: Blue Whale Natural: Forest Fire, Tsunami, disease etc….

Founder Effect Reduced genetic diversity when a small group separates from larger population Example:  Dutch settlers in South Africa have higher instance of Huntington's because original settling population had high occurrence.

2. non-random mating Sexual selection – Individuals compete to mate and pass on their genes WOWSERS! What a HOTTIE!!! Intersexual Selection= One sex chooses the most attractive mate of the opposite sex NO WAY DUDE!! SHE”S MINE! That’s my Girlfriend!! Intrasexual Selection= Same sex individuals “battle” for mates

Mating systems can be either: Monogamous= One male and one female paired for at least one breeding season if not longer Polygynous= One male mates with several females Polyandrous= One female mates with several males (by far the most rare)

3. Mutations occur: Mutation = change in DNA Either random or caused by environmental factors Mutations can be beneficial, neutral, or harmful for the organism. Beneficial ones stick around, harmful do not!

4. Migration occurs Individuals and their genes moving from one population to another. Example: Pollen being blown to a new destination, fish up a new stream, etc. This is called “gene flow” and creates more genetic diversity

Emigration= leaving original population Immigration= entering a new population

5. Natural selection occurs Nature selects who survives to pass on genes “Survival of the Fittest” = struggle for survival Best genes=best traits = survival and offspring= FITTEST “FITNESS” in Evolution is not about being being in shape

Fitness (Survival of the Fittest) The organism that is best suited to its current environment will live AND pass on its genes Example: The brown beetles have a greater fitness relative to the green beetles.

3 Types of Natural Selection Charles Darwin– Described Natural selection After observing nature on his “Voyage of The Beagle in 1830’s” Published “Origin of Species” in 1859 Famous examples: Galapagos finches and torotoises 3 Types of Natural Selection Directional Selection Stabilizing Selection Disruptive Selection

3 Types of Natural Selection 1. Directional Selection – Environment causes an increase in the number of individuals with the trait at one end of the curve.

3 Types of Natural Selection Stabilizing Selection-Individuals in the center of the curve are more fit and thus the curve narrows

3 Types of Natural Selection 3. Disruptive Selection-Individuals at the ends of the curve are more fit than the ones in the middle causing two curves to form and possible new species to form.

Formation of New Species=“Speciation” Species= group of organisms that interbreed and produce fertile offspring Created by evolution (Remember 5 causes!) Boundaries between species can sometimes be unclear Can also be determined by DNA, morphology, and niche http://evolution.berkeley.edu/evolibrary/home.php Life Sciences-HHMI Outreach. Copyright 2006 President and Fellows of Harvard College.

Central Concept of Evolution…. All life on earth shares a common ancestor

Evidence for Evolution: Paleontology- fossil record shows change over time (depth=time) Biogeography- similar species live near each other

Evidence for Evolution: Genetics- similar species have more similar genes in common. We can see relation through DNA Embryology- an embryo displays its ancestral past as it develops

Evidence for Evolution: Morphology- (shape) shows species adapt ancestral structures for new uses Homologous structures-from the SAME ancestral structure Analagous structures- adapted for same purpose but not from the same ancestral structure (ex.- wings on moth, bird, bat