Chapter 19
Genetic Diversity in Populations
Chapter Outcomes:
Define a gene pool.
Describe the gene pool of a population at
genetic equilibrium.
Summarize the five conditions upon which
the Hardy-Weinberg principle is based.
Describe how the Hardy-Weinberg
equation is used to determine whether a
population is undergoing microevolution.
Chapter Outcomes
Calculate allele and genotype frequencies
in a population.
Outline the conditions required to maintain
genetic equilibrium.
Identify and compare the effects of
mutations, gene flow, non-random mating
and genetic drift on gene pool diversity.
Apply the Hardy-Weinberg principle to
published data.
Chapter Outcomes
Distinguish between founder effect and the
bottleneck effect on gene pools.
Explain how the process of natural selection is
related to microevolution.
Explain the cause of heterozygote advantage
and how it affects a gene pool.
Describe strategies used in captive breeding
and population management.
Explain that genetic engineering can have
intended and unintended effects on gene pools.
Genetic Diversity in Populations
Recall that a population is a group of
organisms of the same species living in
one area
Within a population, there are many genes
The sum of the genes (and their different
alleles) is known as the gene pool
Gene pools are studied by population
geneticists
Genotype, Phenotype & Allele
Frequency
Genotype Frequency:
Phenotype Frequency:
Allele Frequency:
The Hardy-Weinberg Principle
the Hardy-Weinberg principle predicts
that if other factors remain constant, the
gene pool will maintain a constant
composition over many generations
this is expressed by a mathematical
equation:
The Hardy-Weinberg Equation
p2 + 2pq + q2 = 1
Where:
p is the frequency of the A allele
q is the frequency of the a allele
if the values of p and q are known, we can
calculate the frequency of the alleles AA,
Aa, and aa (and vice-versa)
Limits to the Hardy-Weinberg
Principle
Large populations
Random mating
No mutations
No migration
No natural selection against any of the
phenotypes
Application of the HardyWeinberg Principle
In a population, we know that a dominant
trait is present 82% of the time. Determine
the percentage of individuals that make up
each genotype.
The Hardy-Weinberg & Population
Change
If a gene pool changes over time, one of
the 5 conditions it is based on must also
have changed
Therefore, the strength of this principle is
to determine whether or not a population is
evolving
The Hardy-Weinberg equation also allows
us to determine what percentage of a
population are “carriers” of a trait
Evolutionary Change
gene pools are unstable
factors that bring about evolutionary
change are mutation, genetic drift, and
migration (or gene flow)
Mutation
Gene Flow
Non-Random Mating
Genetic Drift
The Founder Effect
New populations are often formed by only
a few individuals (Founders)
The founders will only carry part of the
original gene pool from the population
Therefore, the new gene pool will be
limited
The Bottleneck Effect
Starvation, disease, human activities, or
natural disasters can quickly reduce a
large population
The survivors only have a subset of the
alleles present before the disaster, and
therefore, the gene pool loses diversity
Gene pool change caused by a rapid
decrease in population is known as the
bottleneck effect
Examples of the Founder Effect
“Blue Fugates”
Philadelphia Amish
Examples of the Bottleneck Effect
Northern Elephant Seals
Cheetahs
Natural Selection
Natural selection is the only process that
leads directly to evolutionary adaptation
Recall that natural selection occurs in the
following order:
Advantage & Natural Selection
Sexual Selection:
Heterozygote Advantage & Lethal Alleles:
Human Activities & Genetic
Diversity
Humans can affect genetic diversity of
populations in many ways:
1. Habitat fragmentation
2. Unregulated hunting & habitat removal
Biotechnology & Gene Pools
We can use many techniques to modify
organisms and the gene pools of
populations
We now have added genes to species that
come from completely different species,
thereby adding a gene to a gene pool that
most likely would never have been there
otherwise
These genes could be passed on to others
in a population
This could ultimately affect the process of
natural selection
As well, because genes do not work alone
(often they work together), the positive
effect of the inserted genes may be
negated because the gene affects other
traits necessary for survival
Cloning to Save Species
Cloning can be one way to preserve gene
pools
Creating clones of endangered species
could reverse the threat of extinction
In 2000, a cloned Asian gaur (a rare oxlike mammal) was born in Iowa to a
domestic cow that served as a surrogate
mother