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

16.1 GENES AND VARIATION

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?

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

• MENDEL!!! • (Remember, he described INHERITANCE of

“factors” in pea plants).

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

+

• 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.

Genetic Vocabulary Review

• Gene• Trait• Genotype• Allele• Phenotype

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.

• 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

MAIN IDEA!

• Allele Frequency is about finding

(# of A’s)(total # of A’s + a’s)

Application

What is the allele frequency in themice population

Which mice genotypes contain the dominant allele for fur color (B)?

48% heterozygous

black

16% homozygous

black36% 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

***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

black36% homozygous

brown

allele for brown fur

allele for black fur

Each individual has two alleles for a trait, one from mom, one from dad.

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

black36% homozygous

brown

allele for brown fur

allele for black fur

2, the Bb and bb mice

1, 2

****Frequency of a RECESSIVE allele= (# homozygous recessive x 2) + (# heterozygous x 1)(# individuals in population x 2)

48% heterozygous

black

16% homozygous

black36% homozygous

brown

allele for brown fur

allele for black fur

III. Example: Calculating the relative frequencyExample 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)

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

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.

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)

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

• 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!

IV. 2 Sources of Variation: A Review

1.Mutations are any change in the DNA sequence (AATAC AATAT)

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?

• 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.

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?)

Meiosis:• Random assortment of

genes, random separation of chromosomes

(the Law of Independent Assortment).

• Crossing Over: exchanging parts of homologous chromosomes

• REMEMBER! Some variations are better than others, the environment SELECTS those.

• The source of variation is on the DNA level!