Transcript Important to note is that a change in allele

Micro Evolution
-Evolution on the smallest scale
-Evolutionary change within a population
Read p. 468
Chapter 23 Objectives
1. Mutation and Sexual Reproduction produce genetic variation and allow
evolution to occur.
2. To understand the Hardy-Weinberg equation.
3. Natural Selection, Genetic Drift and Gene Flow can alter allele frequencies
within a population
4. Natural Selection is the only mechanism that consistently causes adaptive
Evolution
Only inherited traits are passed on. The color in these caterpillars are due to diet not genetics.
Genetic Variation
-Genetic variation within a population
1. Gene Variability
2. Nucleotide Variability
-Geographic Variation
1. Populations in different
locations can have genetic
variation
2. Some due to Natural
Selection and others by
chance.
Example of chromosomal
changes that spread by drift
or chance events. (No
phenotypic differences
between two populations.)
Cline variation due
to natural selection
Mutations
The ultimate source
of new alleles
1.
Only mutations on gamete forming
cells are passed on. (Not Somatic cell
mutations)
2.
Most mutations aren’t passed on
3.
Point Mutations are changes in at
least one base pair.
Why are most
mutations harmless
or neutral?
1.
Many mutations happen
on the non protein coding
part of DNA.
2.
If mutation does occur on
protein coding portion it
may not change the amino
acid it codes for.
3.
Even if the amino acid
changes it may not
change the shape of the
protein.
Mutations that do alter protein
coding genes.
1.
Deletion, disruption, or rearrangement
of protein coding genes results in
harmful mutations
2.
Duplication can be beneficial.
(Olfactory genes in mammals) p. 471
Sexual Reproduction promotes genetic variation by
1.
Crossing over
2.
Independent Assortment
3.
Random Fertilization
Populations and Gene Pools
-Population is a group of individuals of
the same species that live in the same
area and interbreed.
-Gene Pool is the sum of all alleles
within the population
-Allele Frequency is the total amount of
dominant and recessive alleles in an
environment
Hardy-Weinberg Principle –
Describes a hypothetical
population that isn’t
evolving
-A population whose gene pool will
remain constant or at equilibrium if
only Mendalian segregation and
recombination of alleles is at play
-Gene pool calculation is the sum of all
dominant alleles and the sum of all
recessive alleles
Hardy-Weinberg Conditions
*Populations shift or evolve if at least one
of the below conditions aren’t met
(p. 474)
1.
No mutations occur
2.
Random Mating
3.
No Natural Selection
4.
Extremely large population size
5.
No Gene Flow
*Application example p. 474
-Hardy-Weinberg equation is used to predict percentage of
a genotype being heterozygous or homozygous
p2 + 2pq + q2 = 1
p = one allele
q = different allele
Genetic Drift is a condition
that alters allele frequencies
within a population. P. 476
1. Random events can cause
genetic drift
** Small populations
2. The Founder Effect
3. The bottle neck effect
Possible Outcomes
-Genetic Drift can
lead to loss of
genetic variation
-Genetic Drift can
cause harmful alleles
to become fixed in a
population
Important to note
is that a change in
allele frequency
means the
population is
evolving.
Gene Flow also
contributes to changes in
Allele Frequency
-Transfer of alleles into our out of
a population
-Copper mine example p. 478
Important to note is
that a change in
allele frequency
means the
population is
evolving.
Natural Selection contributes to changing allele frequencies within a population
Individual’s
phenotypic
traits
Genotypes indirectly
contribute to
individual’s relative
fitness
**Natural Selection is
the only condition that
leads to adaptive
evolution
Important to note
is that a change in
allele frequency
means the
population is
evolving.
Gives Individual
Relative Fitness
for Environment
1. Directional Selection
Favors extremes phenotypes
mostly caused by extreme
environmental changes
2. Disruptive Selection
favors phenotypes at both
extremes
3. Stabilizing Selection
favors intermediate
phenotypes
Relative Fitness
leads to an
individual’s
advantage or
disadvantage to
reproduce
Reproductive
success =
passing on
genes and
contributing to
the
population’s
gene pool
Limitations to Natural Selection
p. 484
1. Selection can only act on existing variations
2. Evolution is limited by historical constraints
3. Adaptations are often compromises
4. Chance, Natural Selection and the Environment interact
Frequency
Dependent
Selection p.
484
Sexual
Selection p.
483