Evolution of A new Species Genetic Variation

Sources of Genetic Variety The two main sources of genetic variation in a population are mutations and sexual reproduction Sexual reproduction shuffles parent genes/DNA through meiosis Mutations create constant random variety that sometimes makes an organism more fit for its environment. EX: A mutation that gave brown bears white fur in the polar regions making white polar bears more fit for survival.

“What Molecules Do” Video

Mutations=Variety

Lethal Alleles How are lethal alleles maintained in a population? Shouldn’t natural selection remove these? Alleles that are lethal in a homozygous individual may be carried in a heterozygous individual.

For example: If two parents are carriers of a bad allele and an individual inherits both bad alleles they will get the lethal disease.

Gene Pool- consists of all genes, including all the different alleles, that are present in a population.

Allele Frequency number of times an allele occurs in a gene pool – EX: How many in this class have at least one dominant allele for brown eyes Sexual reproduction produces different phenotypes, but it does not change the relative frequency of alleles in a population.

Gene Pool for Fur Color in Mice

How is evolution defined in genetic terms ? – In genetic terms, evolution is any change in the relative frequency of alleles in a population.

What is Speciation Speciation is the formation of a new species Speciation is caused by reproductive isolation – Reproductive Isolation is when two members of a population cannot mate. There are 3 types of reproductive isolation.

Reproductive Isolation #1. Behavioral Isolation is when genetically similar populations are able to breed but don’t due to differing mating rituals. – A&feature=related A&feature=related – o&feature=related o&feature=related

Reproductive Isolation #2. Geographic Isolation is when two members of a population are separated by barriers such as mountains, canyons, bodies of water, etc. EX: Squirrels on opposite sides of the Grand Canyon

Reproductive Isolation #3. Temporal Isolation is when members of a population mate at different times of the year. EX: Different frogs mate in different months

Equilibrium Theoretical model of a population 5 Conditions: 1) No net mutations 2) NO immigration/Emigration 3) VERY large population 4) Individuals mate randomly 5)Selection doesn’t occur

The Equation Hardy-Weinberg equilibrium=predict population genotypes p=dominant allele (A) q= recessive allele (a) The sum of p+q=1,then solve p 2 + 2pq + q 2 = 1

p=dominant allele (A) q= recessive allele (a) The sum of p+q=1,then solve p 2 + 2pq + q 2 = 1 Use the equation to solve this problem What is p if q = 30% p +.30 =1 p=.70 In this population what percent of individuals are homozygous dominant (AA)? p2=.72=.49=49% In this population what percent of individuals are heterozygous (Aa)? 2pq= 2(.7)(.3)=.42= 42%

Use the equation to solve this problem What is p if q = 30% p +.30 =1 p=.70 In this population what percent of individuals are homozygous dominant (AA)? p 2 =.7 2 =.49=49% In this population what percent of individuals are heterozygous (Aa)? 2pq= 2(.7)(.3)=.42= 42% -PRACTICE

Disrupting Equilibrium 1) Mutations- a change in DNA changes allele frequencies 2) Gene flow- genes move in and out of the population due to immigration and emigration 3) Genetic drift is a change in allele frequencies Genetic drift operates most strongly in small populations 4) Non random mating- whenever individuals may choose partners. Sexual selection occurs when certain traits increase an individual’s success at mating 5) 3 types of selection

Genetic Drift A random change in allele frequency (can be caused by fire, flood, etc) – In small populations, individuals that carry a particular allele may leave more descendants than other individuals do, just by chance.

Genetic Drift

Genetic drift Active art Code cbp-5162

Genetic Drift Descendants Population APopulation B

Founder effect When allele frequencies change as the result of the migration of a small subgroup of a population.

How does genetic drift differ from natural selection in the way it changes the genetic makeup/allele frequency of a species over time?

Stabilizing Selection Favors the formation of average/intermediate traits.

Disruptive Selection Favors extreme traits rather than average traits

Directional Selection Favors the formation of a more-extreme trait.

Does Natural Selection act on the phenotype or genotype of a species? Phenotype – predators can only see the outside physical appearance of an individual making them less fit or suited for their environment.