Biology 100/101
Lectures 23 and 24
Microevolution: The Forces of Evolutionary Change


Announcements

Objectives

Web Resources

Lecture Activity

What is Evolution?

Darwin's Ideas

Artificial Selection

Examples of Microevolution

Hardy-Weinberg

Conditions causing Change

Nonrandom Mating

Migration

Genetic Drift

Mutation

Natural Selection

Balanced Polymorphism

Lecture Syllabus

IB 100/101 Home Page


Genetic Drift

  • Occurs within a small group of individuals when it is separated from a larger population and establishes a new gene pool.
  • Changes in allele frequencies in the isolated, smaller population are random and unpredictable.
  • A new population is formed from a subset of genotypes in the original population.
  • Population Bottleneck: A type of genetic drift occurring when many members of a population die, and a few remaining individuals mate, eventually restoring their numbers. The new population has lost much of the genetic diversity that was present in the larger ancestral population.

    Founder Effect: A type of genetic drift resulting in the establishment of a new, geographically isolated population from a single or very few individuals. It is very unlikely that the gene pool of a founding population is representative of the original population.

      A solitary penguin

      Figure 15.2a, The Founder Effect

      Ellis-van Creveld Syndrome. Small groups of people founding new settlements may have different allele frequencies than the original population, and may also have higher incidents of certain traits (such as genetic disorders) because they marry within the group.

      Ellis-van Creveld is an autosomal recessive disease and occurs in 7% of the people in the Amish community of Lancaster County, Pennsylvania. The occurrence of the disease is high because these Amish marry among themselves. See page 291, text, for more information.

    Founder Effect: A type of genetic drift resulting in the establishment of a new, geographically isolated population from a single or very few individuals. It is very unlikely that the gene pool of a founding population is representative of the original population.

      A solitary penguin

      Figure 15.2a, The Founder Effect

      Ellis-van Creveld Syndrome. Small groups of people founding new settlements may have different allele frequencies than the original population, and may also have higher incidents of certain traits (such as genetic disorders) because they marry within the group.

      Ellis-van Creveld is an autosomal recessive disease and occurs in 7% of the people in the Amish community of Lancaster County, Pennsylvania. The occurrence of the disease is high because these Amish marry among themselves. See page 291, text, for more information.