On truth in Biology : "the only thing always true in biology is that there are always exceptions..." Dr. Rita Calvo Cornell University

microevolut microevoluti microevolutio microevolution

Microevolution: generation-to- generation changes in allele or genotypic frequencies. *genetic changes in a gene pool* look, it’s Jennifer!

Microevolution: allele or genotypic frequency changes… HOW???? 1) Mutations… of germ cells (those that produce gametes!!!)

Microevolution: allele or genotypic frequency changes… HOW???? Point mutations translocations Gene duplication ex. Gene for smell Jumping genes

Microevolution: allele or genotypic frequency changes… HOW???? 2) Sexual recombination

BIG Microevolution causes:

random, evolutionary changes due to chance 1) Genetic drift - random, evolutionary changes in small populations - due to chance … not due to natural selection!!!

The genes of the next generation will be the genes of the “lucky” individuals, not necessarily the healthier or “better” individuals.

If the gene for green coloration drifts out of the population, the gene is gone for good—unless, of course, a mutation or gene flow reintroduces the green gene.

the most important effects of genetic drift: it reduces the amount of genetic variation in a population. And with less genetic variation, there is less for natural selection to work with. If the green gene drifts out of the population, and the population ends up in a situation where it would be advantageous to be green, the population is out of luck. Selection cannot increase the frequency of the green gene, because it’s not there for selection to act on. Selection can only act on what variation is already in a population; it cannot create variation.

BIG Microevolution causes: 1) Genetic drift - (the smaller the sample, the quicker & more drastic the change effect! greater the chance of deviations from the expected probability.)

BIG Microevolution causes: Genetic drift - Population must be large in order to rule out changes due to chance as an agent of evolution

BIG Microevolution causes: Genetic drift - The larger the population, the more closely related the genes will resemble the previous population.

1) BOTTLENECK EFFECT

Certain alleles become under-represented Where did the white ones go?

1) BOTTLENECK EFFECT Some alleles are eliminated altogether orange Where did the orange ones go?

1) BOTTLENECK EFFECT Some alleles are overrepresented Are there proportionally more blue ones now?

BOTTLENECK EFFECT Reduction of population size may reduce gene pool for evolution to work with ex.CHEETAHSex.CHEETAHS Some genes are not represented anymoreSome genes are not represented anymore

FOUNDERS EFFECT New colony

FOUNDERS EFFECT New colony Disproportionate New colony

FOUNDERS EFFECT Genetic drift in a new colony that separates from a parent population. Reduces genetic variability ex. Old-Order Menonite ~ hearing disorder

BIG Microevolution causes: BIG Microevolution causes: 2) Gene flow ( also called migration ) any movement of genes from one population to another. population Gene flow includes many different kinds of events: pollen being blown to a new destination or people moving to new cities or countries. If genes are carried to a population where those genes previously did not exist, gene flow can be a very important source of genetic variation. genes genetic variation

BIG Microevolution causes: BIG Microevolution causes: 2) Gene flow

BIG Microevolution causes: BIG Microevolution causes: Gene flow -

BIG Microevolution causes: BIG Microevolution causes: Nonrandom mating - select a mate based upon phenotype (and what they smell like… hmmmm)

BIG Microevolution causes: BIG Microevolution causes: 4) Natural Selection - over generations, the proportion of favorable alleles survive. All individuals are not equal in their ability to survive & reproduce

Different ways this happens:

characteristics vary: Within the Population

Genetic Variation = Within the Population -

phenotypic polymorphism

Garter SnakesGaillardia phenotypic polymorphism

genotypic polymorphism

Genetic Variation Between Populations - Clinal Along a geographic axis

Selection of genetic variation

N. Selection of genetic variation Here is the base-line:

Selection of genetic variation stabalizing selection: ex. Birth weight in babies

Elimination of extreme phenotypes. Favors intermediate This reduces variation Selection of genetic variation Stabalizing selection:

Selection of genetic variation Directional Selection: ex. Galapagos Island finch beak size

Elimination of intermediate phenotypes. Favors the rare This reduces variation Selection of genetic variation Directional Selection:

Selection of genetic variation Selection of genetic variation Diversifying Selection:

Elimination of intermediate phenotypes. Favors the extremes. This reduces variation Selection of genetic variation Selection of genetic variation Diversifying Selection:

Question Does evolution result in perfect organisms?

Misconception: “Natural selection gives organisms what they ‘need.’ ”

Summary Know the difference between a species and a population. Know that the unit of evolution is the population and not the individual.

Summary Know the H-W equations and how to use them in calculations. Know the H-W assumptions and what happens if each is violated.

Summary Identify various means to introduce genetic variation into populations. Know the various types of natural selection.