Chapter 4

Genes and their Evolution: Population Genetics

• Evolution occurs in populations

• Gene pool: All the genetic information in the breeding population

• Species are defined on the basis of their reproductive isolation. There are several mechanisms that keep different species from interbreeding

• How does reproductive isolation begin?

  • Usually because of geography. Little differences in each group start to accumulate once they’re physically isolated from each other

    • Changes in behavior

    • Changes in the shape of the genitalia

    • Changes in odors, pheromones

    • And each subgroup is starting to adapt to environmental differences

• Know

  • Little changes accumulating = microevolution

    • Changes in allele frequency that occur from one generation to the next

  • Macroevolution is large scale evolution

    • Such as a speciation event, that occurs after hundreds or thousands of generations

    • Reproductive isolation

      • Two related bird species: Ostriches are found in Africa, while Emus are found in Australia

• Speciation

  • Cladogenesis: a new species splitting off. Thought to be common

• Extinction

  • The loss of a species due to the disappearance of its members

  • Extinction is a common fate. Most species that have ever existed on the earth are now extinct

  • Sooner or later a species will encounter such severe stresses it will die

• Human Variability

  • Anatomical features such as skin color

  • Physiological traits such as metabolic rate

  • Characteristics of the blood

  • We respond most to differences we see

• Human Blood Groups

  • Red blood cells carry proteins on their surfaces that function as ‘antigens’

  • Antigens = any organic substances, recognized by the body as foreign, that stimulate the production of antibodies

  • Antibodies = proteins produced by the immune system as a defense mechanism to attack foreign substances invading the body

  • Agglutination = the clumping of red blood cells as a result of the reaction of antibodies to an antigen

• Genes and disease

  • B allele helps protect against infant diarrhea

  • A and B alleles help protect against the plague

  • O allele protects against bronchial pneumonia

  • Rh- is less susceptible to small pox…

• The four forces of evolution

  • Mutation

  • Natural Selection

    • Directional

    • Stabilizing

    • Disruptive

  • Genetic Drift

  • Gene Flow

• Mutation: The Only Source of New Alleles

  • Mutation is the only source of new genetic information

  • Mutation can be any heritable change in the structure or amount of genetic material

  • Changes can be as small as one base pair substitution, or as large as inheriting the wrong number of chromosomes

  • New alleles are always forming through mutation

  • But if an allele’s frequency is 1% or higher, it’s not just there because of mutation

    • something increased its presence in the gene pool

  • Ply morphism

    • The presence of 2 or more alleles at a locus and where the frequency is greater than 1% of the population

• Natural Selection

  • Based on Darwin’s principle that individuals with advantageous characteristics will survive and reproduce in higher numbers (reproductive success)

  • Patterns of Natural Selection

    • Directional selection favors an extreme form of a trait

      • The increasing size in mammoths and other mammals during the Ice Ages (warm-blooded animals can hold onto their body heat better if they are big)

      • The increasing size of the human brain over the last 2 million years (gave humans survival advantages)

    • Stabilizing selection favors the average form of a trait

    • Disruptive selection favors individuals at both extremes

  • Examples of directional selection

    • The increasing size of mammoths and other mammals during the Ice Ages (warm blooded animals can hold onto their body heat better if they are big)

    • The increasing size of the human brain over the last 2 million years (gave humans survival advantages)

  • Examples of stabilizing selection

    • Living fossils are a great example of stabilizing selection

    • Carcharocles angustidens

  • Examples of disruptive selection

    • Finch beak size

  • Natural Selection in Animals: The Case of the Peppered Moth and Industrial Melanism

    • Numerous examples exist for natural selection in animals

    • The peppered moth is the best evidence of natural selection documented

    • The peppered moth was found in England

    • It had two forms: light and dark

Mutations provide the variation and then natural selection can act on them

Malaria is caused by a parasite named Plasmodium, carried by female mosquitoes