Evolutionary Mechanisms: Microevolution
Objectives
Identify the mechanisms that produce change in allele frequencies.
Test hypotheses about allele frequencies using simulations
Draw conclusions about how effective different evolutionary mechanisms can be.
You, as an individual, have a whole set of genes, your genome, which are segments of the DNA
molecules we call chromosomes. The genes code for building and maintaining you as a living
creature. Can you (or any individual) evolve in the biological sense? In other words, will your
alleles, the different versions of a particular gene, change over your lifetime?
You share genes with other humans and it is possible to determine allele frequencies for a
population, members of a species that share a particular area at a specified time. The sum total
of these genes in a population is called the gene pool. Population membership changes over
time. Think of some ways in which this could happen. If population membership changes,
would you expect that, under certain conditions, allele frequencies in this population could
change over time as well?
This is the topic of today’s lab—how allele frequencies can change over time or the mechanisms
of evolution. If allele frequencies are significantly changing over time, the population has
evolved. To observe evolution, we would need to look at several generations (perhaps 100’s or
1000’s) of a population. This would be difficult to achieve in a three-hour laboratory. Even
bacteria need approximately a half-hour to reproduce! Instead, you will use simulations
(simplified models of the real thing) to determine if and how evolution of population occurs. The
primary goal of this lab is to give you insight about how evolution can and does work.
Review of Mendelian Genetics
It is important to distinguish an individual’s appearance, or phenotype, from the alleles present in
that individual’s cells. Every individual carries two alleles of a given gene; the description of
these alleles is a genotype. Recessive alleles are those that are masked or hidden by another
allele. For example, the allele for blue eye color (recessive) is masked by an allele for a pigment
such as brown. Pigment is thus dominant over blue. By convention, recessive alleles are denoted
be lowercase letters and dominant alleles by uppercase letters. If “P” stands for pigment and “p”
stands for nonpigmented eye color, then blue-eyed individuals have the genotype “pp” since they
have two recessive alleles, while individuals with pigmented eyes are either “Pp” or “PP”.
We cannot identify the correct genotype for the pigmented phenotype unless we gain more
information about parents and/or offspring, since it takes only one dominant allele to mask a
recessive allele. Note that some genotypes involve identical pairs (“pp” and “PP”, called
homozygous (alike) and some involve a mixed pair (“Pp”, called heterozygous).
Most human traits, such as facial features, height, dexterity, etc. are controlled by numerous
alleles, and many of these have complex interactions among themselves and with the
environment. These traits can be very difficult to study. Some human physical and biochemical
traits are controlled through the inheritance of single genes with two or more alternate alleles, for
example traits such as blood type. We will examine eight such traits in this class.
Bi 102 Laboratory Microevolution 1
