Transcript Ch 023 evolupop

The Evolution of Populations
•Darwin and Mendel’s discoveries merged.
•Darwin’s theory of natural selection
•Mendel’s inheritable information
•Population Genetics: genetic variation within a
population
•Modern Synthesis: 1940’s; integrated discoveries
Population is the unit of evolution
Natural selection is means of mechanism
Gradualism: large changes evolve from
small changes over long period of time.
Genotype Frequencies
Population: Localized group of individuals belonging to the
same species.
Species:
Individuals that have the potential to interbreed
and produce fertile offspring in nature.
Gene Pool: Total aggregate of genes in a population at any
on time. Consists of all alleles at all gene loci in
all individuals of the population
Diploid, locus, fixed pop.,
•Individuals are selected but
•Populations evolve.
Imaginary Population of Flowers
• R is Dominant (Red), r is recessive (white)
• 500 plants (20 are white, HR)
• 480 are red meaning R? (HD or Ht)
•IF
•320 are RR and 160 are Rr……then
1. How many copies of the gene are
there in the population?
2. How many genes are dominant?
Recessive?
3. What are the percentage of each
•1000 genes
•800 dominant
•200 recessive
•80%....20%
Hardy-Weinberg Theorem
Frequencies of alleles and genotypes in a population’s gene pool
remains constant over the generations unless acted upon by other
agents. The number of times an allele occurs within a population.
p= frequency of dominant allele
q= frequency of recessive allele
p+q=1
Hardy Weinberg Equation
p2 + 2pq
Frequency
of AA
genotype
Frequency
of Aa +aA
genotype
+
q2 = 1
Frequency
of aa
genotype
•PKU: recessive allele disease
1 in 10,000 births (q2=0.0001)
•What percentage of US
population are carriers?
Solution
• One PKU per 10,000 births….
• q2 = 0.0001 frequencies of HR
•Therefore….q = √0.0001 = 0.01 Frequency of
Reccesive Allele
•Frequency of Allele is p + q = 1 and if q = 0.01
•then p = 0.99
•Now using HW Equation solve for 2pq
•2pq = 2 x 0.99 x 0.01 = 0.0198 or close to 2%
•2% of the Population are PKU Carriers.
You Solve
1. Allele Frequency of B is 0.7, what would the
frequency of heterozygotes by if in HW
equilibrium? Frequency of recessive allele?
0.42
0.30
1. 313 out of 1432 individuals have a recessive
disorder. What percentage of this population are
carriers?
50%
2. If 511 individual out of 2315 show the
characteristic of a DOMINANT disorder, what is
the frequency of the recessive allele? How many
individuals would be show the recessive trait?
0.53
648 INDIV.
Microevolution
Changes of the gene pool of a population at the
smallest level.
Frequencies of Allele in a population.
5 Conditions needed for HW Eq.
1.
2.
3.
4.
5.
Very Large Populations:
Isolation from other populations
No Net Mutations
Random Mating
No Natural Selection
•A deviation from HW eq. in a gene pool
signifies evolution
•Natural Population are not EXPECTED to
be in HW eq.
5 Agents of Microevolution
1. Genetic Drift: changes in the gene pool of a
small population
Genetic Drift can be caused by:
A. Bottleneck effect: Disaster eliminates large population.
Surviving population is not represented of the original.
Genetic variability is low
B. The Founder Effect: Genetic drift may occur when a
smaller colony breaks away from original. (Darwin’s Finches)
Cause of Microevolution Cont.
2. Gene Flow: genetic exchange due to alleles
migrating in or out of a population. Will
tend to reduce differences b/w populations.
3. Mutations: Change in DNA of an organism. Must
occur in gametes, rare occurrence of this occurring.
Cause of Microevolution Cont.
4. Nonrandom Mating: “Inbreeding”; relative
frequency of genotypes deviate from H-W.
W/ each generation Heterozygote # decreases.
Assortive Mating: selecting partners with
similar characteristics.
5. Natural Selection: differential success of
reproduction. Most likely agent to cause
microevolution. Selects favorable genotypes
Inheritable Variations
•Differences can occur between populations
•Quantitative Variations occur along a continuum.
•Polymorphism: Two or more contrasting forms (morphs)
of a characteristic. High frequency of alleles of
all forms.
Ex: garter snakes, freckles, Blood type (ABO).
Variation Between
Populations
•Geographical Variations: differences b/w pop (or w/i). due
to environmental factors. Natural selection and
genetic drift can cause.
Cline: graded change in a trait along a geographic
axis.
Mutations generate Genetic
Variations
•Mutation:
•Point mutations mostly harmless, occur
in somatic cells. Rarely will cause mutant
allele allowing for better reproduction success.
•Chromosomal Mutation: disrupts development
may have benefits.
•Bacteria: reproduce every 20 minutes, mutation
in one may produce millions in an hour.
Antibiotic resistant bacteria
Natural Selection as a means of
Evolution
•Darwinian Fitness: the measure that is critical to
selection, is the relative contribution an
individual makes to the gene pool of the next
generation.
•Relative Fitness: contribution of a genotype to the
next generation compared to another. Based as
a % based on best reproductive member (1).
Modes of Selections
•Diversifying Selection: environmental factors
favors extreme individuals at both ends.
•Directional Selection: changes that occur when
moving to new area with different conditions.
•Stabilizing Selection: cuts extreme varients, reduce
phenotypic variation, status quo
Natural Selection and Perfection
•Natural Selection cannot produce perfection
•WHY???
1.
2.
3.
4.
Evolution is limited by historical constraints
Adaptations are often compromised
Not all evolution is adaptive
Selection can only edit existing variations