Examples of Evolution

Allele Frequencies There are dominant and recessive alleles. Hardy and Weinberg (scientists) determined that dominant alleles do NOT automatically replace recessive alleles. Alleles in a population only change if selection acts upon them nid=vSsuBQ-o-EFlxM:&tbnh=131&tbnw=219&ei=- 6ahTYjRF6iU0QGo5JSEBQ&prev=/images%3Fq%3Dpterodactyl%26um%3D1%26hl%3Den%26rlz%3D1G1GGLQ_ENUS398%26biw%3D1438%26bih%3D680%26tbm%3Disch&um=1&itbs=1&iact=hc&vpx=1109&vpy=148&dur=18 95&hovh=174&hovw=290&tx=91&ty=85&oei=-6ahTYjRF6iU0QGo5JSEBQ&page=1&ndsp=19&ved=1t:429,r:5,s:0

HARDY- WEINBERG PRINCIPLE: The frequencies of alleles in a population do not change unless evolutionary forces act on the population.

Hardy-Weinberg Holds true for: large populations in which members do not mate with relatives AND as long as evolutionary forces are not acting on the population

5 Evolutionary Forces 1. Mutations 2. Gene Flow 3. Nonrandom mating 4. Genetic drift 5. Natural Selection

#1 Mutations Mutation rates are slow in nature Not all result in phenotype changes (remember the codon wheel) Mutation IS the source of variation though & makes evolution possible odFQbQMhttp:// odFQbQM

#2 Gene Flow The movement of individuals to or from a population (MIGRATION) creates gene flow. Immigrants = arriving individuals Emigrants = departing individuals

#3 Nonrandom Mating In-breeding alters Hardy-Weinberg Also occurs when organisms choose their mates

#4 Genetic drift Small populations that are isolated from one another can differ greatly because of genetic drift Fires - landslides - etc.

# 5 Natural Selection The frequency of an allele will increase or decrease depending on the allele’s effects on survival and reproduction N.S. is one of the most powerful agents of genetic change.

Natural Selection affects the Distribution of Phenotypes in 4 Ways! 1 – Stabilizing Selection 2 – Directional Selection 3 – Disruptive Selection 4 - Sexual Selection

1- Stabilizing Selection Individuals with the average form of a trait have the highest fitness.

2 – Directional Selection Individuals at one end of the curve have higher fitness and are favored more than individuals in the middle or other end.

3 – Disruptive Selection Individuals with either extreme variation of a trait have greater fitness than individuals with the average form of the trait.

4 – Sexual Selection The preferred choice of a mate based on a specific trait. Peacocks -- females choose males based on certain traits

V. I.S.T. V = Variation: All life forms vary genetically within a population. It is this genetic variation upon which selection works. I = Inheritance: Genetic traits are inherited from parents and passed on to offspring. S = Selection: Organisms with traits that are favorable to their survival get to live and pass on their genes to the next generation. T = Time: Evolution takes time. It can happen in a few generations, but major change, such as speciation, often take very long periods of time.