Population Genetics and Speciation Chapter 16 Evolution O

Population Genetics and Speciation Chapter 16

Evolution • O. Understand the mechanisms that can cause change in the genetics of a population. • J. Explain the 4 steps in the process of natural selection as explain by Darwin

Evolution and Genetics • Microevolution: the change in the collective genetic material of a population. • Populations are the smallest unit in which evolution occurs.

Section 1 • Population biologists study many different traits in population such as size and color

• Traits vary and can be mapped along a bell curve, which shows that most individuals have average traits, whereas a few individuals have extreme traits.

What causes variation? • Could be environmental…. but most often it is heredity • Variations in genotype arise in three different ways: – Mutation – Recombination – Random pairing of gametes

Gene Pool the total genetic information available in a population

This can be used to determine the frequency of the alleles for a particular trait in a population • Assume a gene pool of 10 gametes for a gene which is controlled by only 2 alleles – 8 are allele A – 2 are allele a – Frequency of A is 8/10 or. 8 – Frequency of a is 2/10 or. 2 – How many light blue individuals would you expect in a population of 100? 0. 2 X 0. 2 =. 04 or 4 light blue individuals.

Hardy-Weinberg: showed allele frequencies don’t change unless they are acted on by outside forces. • So… a population that is not evolving: – 1. – 2. – 3. – 4. – 5. no mutation no individuals enter or leave the population is very large individuals mate randomly selection does not occur

Does this ever happen? NO!

Disruption of Genetic Equilibrium • Mutation: affect genetic equilibrium by producing totally new alleles for a trait. • Gene flow: the movement of individuals into or out of a population causes gene flow– the process of genes moving from one population to another • Genetic Drift: the change of allele frequencies in a population due to random chance. Happens most often in small populations.

Nonrandom Mating is nonrandom whenever individuals may choose partners. Sexual selection occurs when certain traits increase an individual success at mating. Sexual selection explains the development of traits that improve reproductive success but that may harm the individual bright colors = sexy bright colors = more visible to predators.

Natural Selection • Can influence evolution in one of three general patterns. – Stabilizing selection favors the formation of average traits – Disruptive selection favors extreme traits rather than average traits. – Directional selection favors the formation of more -extreme traits.

Formation of Species • A species is a population of organisms that can successfully interbreed but cannot breed with other groups • Geographic isolation results from the separation of population subgroups by geographic barriers. Geographic isolation may lead to allopatric speciation.

• Reproductive isolation results from the separation of population subgroups by barriers to successful breeding. • Reproductive isolation may lead to sympatric speciation. • In the gradual mode of speciation, species undergo small changes at a constant rate. • In punctuated equilibrium model, new species arise abruptly differ greatly from their ancestors and then don’t change for long period of time.

Rates of Speciation Gradualism Punctuated Equilibrium