Natural Selection Notes 2 Moths and Natural Selection Spoons Evidence for Evolution Notes 3 Comparative Anatomy Biogeography DNA Packet Video Webquest Biochemical Comparisions Mechanisms of Evolution ID: 929992
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Slide1
Where we’ve been:
Charles Darwin and his travels (Darwin Notes 1)
Natural Selection (Notes 2)
Moths and Natural Selection Spoons
Evidence for Evolution (Notes 3)
Comparative Anatomy, Biogeography, DNA
Packet, Video,
Webquest
, Biochemical
Comparisions
Mechanisms of Evolution (
webquest
and
this
)
Genetic Drift, Sexual Selection, Mutation, Migration, Natural Selection
Slide216.1 GENES AND VARIATION
Slide3I.
“Gaps” in Darwin’s Theory
1. How do
VARIATIONS
arise? -Variation was one of the key “ingredients” of NATURAL SELECTION
- Remember:
variation, selection, time- Some variations are better than others, the environment SELECTS those. 2. How are FAVORABLE variations (traits) passed on to offspring?
Slide4What scientist’s work could have help Darwin with these questions?
Slide5MENDEL!!!
(
Remember, he described
INHERITANCE
of “factors” in pea plants).
Slide6II. Putting it all together!
By the 1930s, Mendel and Darwin’s work were combined. Molecular biologists had also discovered that:
1) DNA was the molecule of heredity.
DNA
determines phenotype.
2) Sources of variation include MUTATION and GENE SHUFFLING
+
Slide7We can now describe evolution in
GENETIC
terms. We can be more specific than “
change
over time.” Evolve: change over time
Evolution
(in genetic terms) is any CHANGE in the relative FREQUENCY of ALLELES in a population.ORAKA:
biological evolution
or
microevolution
A change in genetic composition within a population over generations.
Slide8Genetic Vocabulary Review
Gene
Trait
Genotype
AllelePhenotype
Slide9Vocab:
1. A
POPULATION
is a group of individuals of the same species that interbreed and reproduce.
2. A GENE POOL is all genes, including different alleles, that are in a population.
Slide103.
RELATIVE FREQUENCY
is the # of times an allele appears in a population.
General Equation
:
Relative frequency of an allele=
# of the certain allele in the population # of TOTAL alleles in the population
Slide11MAIN IDEA!
Allele Frequency is about finding
(# of A’s)
(total # of A’s + a’s)
Slide12Application
What is the allele
f
requency in the
mice population
Slide13Which mice genotypes contain the dominant allele for fur color (B)?
48% heterozygous black
16% homozygous black
36% homozygous brown
allele
for
brown fur
allele for black fur
2, the BB and Bb mice
How many dominant alleles are in the homozygous dominant black mouse? The heterozygous mouse?
2, 1
Slide14***Relative frequency of a DOMINANT allele
=
(# homozygous dominant
x
2) + (# heterozygous x 1)
(# individuals in population
x 2) Why multiply the # of individuals by 2?
48% heterozygous black
16% homozygous black
36% homozygous brown
allele
for
brown fur
allele for black fur
Each individual has two alleles for a trait, one from mom, one from dad.
Slide15Which mice genotypes contain the recessive allele (
b
)?
How many recessive alleles are in the heterozygous mouse? The homozygous recessive mouse?
48% heterozygous black
16% homozygous black
36% homozygous brown
allele
for
brown fur
allele for black fur
2, the Bb and bb mice
1, 2
Slide16****Frequency of a RECESSIVE allele=
(# homozygous recessive x 2) + (# heterozygous x 1)
(# individuals in population
x
2)
48% heterozygous black
16% homozygous black
36% homozygous brown
allele
for
brown fur
allele for black fur
Slide17III. Example: Calculating the relative frequency
Example 1: Let's consider a gene with only two alleles. In mice, Black fur color (BB or Bb) is dominant to brown fur color (bb).
In a population of 100 mice, 36 mice are homozygous dominant (BB), 48 mice are heterozygous (Bb) and 16 are brown (bb).
Relative frequency of B=
# of B alleles in the population
# of TOTAL alleles in the population
Relative frequency of a
dominant
allele:
=
(# homozygous dominant x 2) + (# heterozygous x 1)
(# individuals in population x 2)
Slide18Relative frequency of B
=
(36
x
2) + (48
x
1)
= .60 = 60%
(100 x 2) = 200
or
36+36+48
=
120
= 60%
100+100 200
How could we figure out the frequency of “
b
” without doing the big equation?
0.6 + 0.4 =1.0
Slide19Note that the allele frequencies add up to 1. *This is a law of population genetics:
The sum of all allele frequencies
will always be equal to 1
.
This is because 1 represents the frequency of all possible alleles within the population.
Slide20Frequency of b?
Frequency of
b
=
# of
b
alleles in the population # of TOTAL alleles in the population
Frequency of a recessive
allele:
=
(
# homozygous recessive x 2) + (# heterozygous x 1
)
(
# individuals in population x 2)
Slide21Frequency of
b
=
(16 x 2) + (48 x 1)
=
80
= 0.4 = 40%
(100 x 2) = 200 200
or
(16 + 16 + 48)
=
80
= 0.4 = 40%
(100
+100 )
=
200
Note that the two allele frequencies
add up to
ONE.
0.6 + 0.4 =1.0
Slide22Let’s say that these mice have several generations of offspring. We want to know if EVOLUTION
has occurred. How would we know?
If the relative frequencies of the alleles
CHANGE
, then evolution has occurred!
Slide23IV. 2 Sources of Variation: A Review
1.Mutations are any change in the DNA sequence (AATAC
AATA
T
)
May be caused by:Mistakes during replicationRadiation or chemicals in the environment Effects: INCREASE Fitness, DECREASE
Fitness, or
NO
Effect
When would a mutation have no effect?
Ex: Silent mutation, no change in amino acid sequence
Clip: Why don't horses have wheels?
Slide24When would a mutation that caused a phenotypic change have no effect on fitness?
If it were something that did not effect
SURVIVAL
and
REPRODUCTION
. Ex. extra finger or extra teeth.
Slide252.
Sexual Reproduction (Gene Shuffling)
Q: Why don’t you look exactly like your parents? (what were the sources of genetic variation you learned in meiosis?)
Slide26Meiosis
:
Random assortment of genes, random separation of chromosomes
(the
Law of Independent Assortment).
Crossing Over
: exchanging parts of homologous chromosomes
Slide27REMEMBER! Some variations are better than others, the environment
SELECTS
those.
The source of variation is on the
DNA level!