Chapter 16 Population Genetics and Speciation 16-1 Genetic Equilibrium

Terms to Know Population genetics – study of evolution from a genetic point of view Microevolution – evolution at the genetic level Bell Curve – most members of the population have similar traits; only a few are at the extremes Can SHIFT over time!!!

Variations of Traits Within a Population Causes of Variation Mutations TAGATC -> TAAATC Recombination (crossing-over and independent assortment) (during meiosis – see pic!) Random pairing of gametes Which sex cells combine successfully

The Gene Pool Gene pool = the total genetic information available in a population Allele Frequency = number of a certain allele / total number of alleles in a population Calculated by … # of allele A total # of A and a

What is the allele frequency? Half a population of four o clocks are red/ half are white. What is the frequency of the r allele? 0.50 or 50%

The Gene Pool Phenotype Frequency = # of individuals with a phenotype / total # of individuals within the population

The Gene Pool Phenotype Frequency = # of individuals with a phenotype / total # of individuals within the population # red flowers/ Total # of individuals

Hardy – Weinberg Genetic Equilibrium Ideal hypothetical population that is not evolving (ie not changing over time) 5 criteria (must be met) No net mutations occur No one enters or leaves the population The population is large Individuals mate randomly Selection does not occur Why might a population never be in HW genetic equilibrium???

Assignment Pg 320 Q’s (1-5) Answer in complete sentences! Turn in when completed! Read pg’s 321-325 and answer the Q’s given.

16-2 Disruption of Genetic Equilbrium

Mutation Gene flow – the process of genes moving from one population to the next - Immigration - Emigration 3. Genetic Drift – allele frequencies in a population change usually because the population is small

4. Nonrandom mating – mate selection is influenced by geographic proximity, mates with similar traits, and sexual selection

- stabilizing selection - disruptive selection - directional selection 5. Natural Selection – some members are more likely to survive and reproduce - stabilizing selection - disruptive selection - directional selection

Types of Selection Stabilizing selection - individuals with average forms of a trait have the highest fitness Ex. Large lizards will be spotted by predators; small lizards can’t run fast enough to get away from predators

Types of Selection Disruptive Selection – individuals with either extreme of the trait has the greatest fitness Ex. White moths on white trees cannot be seen; Dark moths on dark trees cannot be seen; medium colored moths will be seen on both trees (eaten by birds)

Types of Selection Directional selection – more extreme form of a trait has the greatest fitness Ex. Anteaters with the longest tongues will get the most food

16-3 Formation of Species

The Concept of Species Speciation – the process of species formation Morphology – internal and external appearance of an organism Species – morphologically similar and can interbreed to produce fully fertile offspring

Morphological vs Biological Species Concept 2 competing concepts (ideas) on how to determine different species Morph = based solely on appearance Bio = based on who can reproduce with who successfully (not useful for extinct or asexual organisms) What do we use today? Mix of BOTH!!!

Isolation and Speciation Geographic isolation – physical separation of members of a species Ex. River dries up into several small pools; fish diverged enough to be considered separate species

Reproductive Isolation – species become genetically isolated Ex. The offspring of interbreeding species may die early or may not be fertile Ex. Different mating times

Rates of Speciation Gradualism – speciation occurs at a regular, gradual rate Punctuated Equilibrium – sudden, rapid change then long periods of no change