Where we’ve been: Charles Darwin and his travels (Darwin Notes 1) - PowerPoint Presentation

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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

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16.1 GENES AND VARIATION

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I.

“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?

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What scientist’s work could have help Darwin with these questions?

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MENDEL!!!

(

Remember, he described

INHERITANCE

of “factors” in pea plants).

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II. 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

+

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We 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.

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Genetic Vocabulary Review

Gene

Trait

Genotype

AllelePhenotype

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Vocab:

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.

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3.

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

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MAIN IDEA!

Allele Frequency is about finding

(# of A’s)

(total # of A’s + a’s)

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Application

What is the allele

f

requency in the

mice population

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Which 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

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***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.

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Which 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

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****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

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III. 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)

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Relative 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

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Note 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.

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Frequency 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)

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Frequency 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

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Let’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!

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IV. 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?

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When 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.

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2.

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?)

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Meiosis

:

Random assortment of genes, random separation of chromosomes

(the

Law of Independent Assortment).

Crossing Over

: exchanging parts of homologous chromosomes

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REMEMBER! Some variations are better than others, the environment

SELECTS

those.

The source of variation is on the

DNA level!