Download Bio 30 Unit D1 Population GeneticsTAR

POPULATION GENETICS
BIOLOGY 30
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: is a measure of the fraction, ration, or percent
of the homozygotes and heterozygotes in a population sample for
the given variations in a trait
• Phenotype Frequency: is a measure of the fraction, ratio, or percent
of the offspring or sample population expressing either the dominant
or recessive variations of a trait (could also have intermediate
variations)
• Allele Frequency: is a measure of the fraction, ratio, or percent of the
one variation occurring in the gametes of a populaiton
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 EQUATIONS
p2 + 2pq + q2 = 1(genotype frequency
where phenotype can be interpreted)
p+q = 1(allele/gamete frequency)
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
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Large populations
Random mating
No mutations
No migration
No natural selection against any of the
phenotypes
These are to maintain no significant change in the gene pool and
are usually limited to shorter periods of time
APPLICATION OF THE HARDY-WEINBERG
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 in that they are constantly
responding to both the biotic and abiotic changes
in their ecosystems
• Evolutionary change takes time, especially with Kselected populations and involves Agents of
Change …
AGENTS OF CHANGE
1. Mutation (changes in the nucleic base sequence
causing a change in protein production)
2. Non-random mating (survival of the fittest)
3. Non equal viability (struggle to exist with competition)
4. Genetic Drift (chance changes in populations –
Founder Effect and Bottleneck Effect
5. Gene Flow (migration of gene pools)
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
• Examples:
• Blue Fugates
• Philadelphia Amish
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:
• Northern Elephant Seals
• Cheetahs
NATURAL SELECTION
• Natural selection is
the only process
that leads directly
to evolutionary
adaptation
• Example:
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Sexual Selection
Heterozygote Advantage
Lethal Alleles
Alpha Males
Reproductive Isolation
Geographic Isolation
• Recall that natural
selection occurs in
the following order:
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Variation
Overproduction
Struggle to Exist
Survival of the Fittest
Origin of a New Species
HUMAN ACTIVITIES & GENETIC DIVERSITY
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1.
2.
3.
4.
5.
Humans can affect genetic diversity of
populations in many ways:
Habitat fragmentation
Unregulated hunting & habitat removal
Introduction of mutagens
Introduction of non-native species
Introduction of new genomes to give one species
an advantage over another
CLONING TO SAVE SPECIES
• Cloning can be one way to preserve ancient gene
pools
• Creating clones of endangered species could
reverse the threat of extinction
• In 2000, a cloned Asian gaur (a rare ox-like
mammal) was born in Iowa to a domestic cow that
served as a surrogate mother