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Ch 16 Population

Genetics and

Speciation

1. What is population genetics?

• The study

of evolution

from a

genetic

point of

view.

2. What is microevolution?

• Evolution at the genetic level

• A change in the collective genetic material

(genes) of a population.

2. What is microevolution?

• Genetic Material – the many

alleles or variations of the

many genes that code for

various traits

3. What is a population?

• A population consists of a group of

individuals of the same species that

routinely interbreed • same SPECIES

• same PLACE

• same TIME

– Example: all the trout in Dos Picos pond

Could this be a single population?







4. Why are populations important

to the study of evolution?

• A population is the smallest unit in which

evolution occurs.

4. Why are populations important

to the study of evolution?

• Natural selection favors an increase in the

genes of successful reproducers rather

than merely those of successful survivors.

5. In populations in nature, what patterns

are seen in certain quantitative traits?

• Quantitative traits, such as height and

weight tend to follow a bell curve pattern

Skill Builder

• Make a line graph of the following human

height data: 11 people are 160 cm tall, 61

are 165 cm tall, 149 are 170 cm tall, 199

are 175 cm tall, 153 are 180 cm tall, 58

are 185 cm tall, and 9 are 190 cm tall.

• Describe the shape of the distribution

6. What are things that can affect

species within a population?

• Environmental factors such as the amount

or quality of resources available to an

organism.

6. What are things that can affect

species within a population?

• Heredity / genetics

7. What causes genes to vary

within a population? A. Genomic Mutation – a random change in

genes that is passed on to offspring. This

may change or add alleles within a

population.

B. Recombination – the reshuffling of genes

in a diploid individual during meiosis


within a population?

C. The random

pairing of

gametes during

sexual

reproduction


within a population?

1. What three things cause genes

to vary?

2. Why is it important to have

variation within a population?

8. What is a gene pool?

• The total genetic information in a

population.

• Allele frequency: how common a specific

allele is within a population

• Phenotype frequency: how common a

specific phenotype is within a population

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.2

.9

.1

Figure 16-3

• Open the textbook to page 319 and look at

figure 16-3

• Use this figure to explain how allele

frequency is determined

• How could a white flower appear in the

second generation when there were no

white flowers in the first generation?

Flower Color • The red and white squares represent white, r,

and red, R, alleles in four o’clock flowers.

What are the allele frequencies?

• Put the alleles in a pile. Have each person in

your group with eyes closed put them in

pairs.

• Write down the genotypes and determine the

phenotypes and phenotype frequencies.

• Compare your results with other

groups.

9. What is genetic equilibrium?

• The state within a population at which the

frequency of alleles and genotypes does

not change from generation to generation.

• When a population is in genetic

equilibrium it means no evolution is

occurring

10. What forces disrupt genetic

equilibrium causing evolution to occur?

1. Mutation: a change

in the DNA of an

organism resulting

in new alleles, which

change the

population.



2. Gene Flow – the

process of genes

moving from one

population to

another



2. Immigration: new individuals enter the

population

Emigration: individuals leave the

population



3. Non-random mating: individuals pair by

choice not by chance



4. Genetic Drift: the phenomenon by which

allele frequencies in a population change

as a result of random events or chance.



• Study figure 16-5 on page 322 and answer

the following:

– What is the graph comparing?

– Which line on the graph represents a

population in which the frequency of the allele

changes very little over many generations?

– What is the significance of the green

line intersecting the x-axis?



Genetic drift occurs more rapidly and has a

greater affect on small populations

Small population = small gene pool = less

genetic information

Check it…

• Why is genetic variation so important???



Example: Genetic bottleneck

A genetic bottleneck occurs when

environmental disturbances cause

populations to become so small that

inbreeding occurs which often leads

to decreased genetic variability.



Over evolutionary time, populations with low

variability are less likely to survive in

changing environmental conditions.

Examples: cheetahs and black footed ferrets



5. Selection: one of the strongest

evolutionary forces

a) Natural selection: Darwin’s theory.

The environment selects against

individuals that cannot survive AND

reproduce. This acts on the

PHENOTYPE of the

organism

b. Sexual Selection

• When one of the genders (male or

female) chooses a mate based on the

phenotype or certain traits.

• e.g. Female peahens choose attractive

peacocks



c. Sexual Dimorphism

• When the appearance of the female is

different from the appearance of the

male.

• e.g. Male lions have a

mane, female lions

don’t



Sexual Dimorphism

in Antelope

c. Artificial Selection

• When humans select a specific trait and

breed for that specific trait.

– Dogs, livestock, farming



Thought Question….

• What five things cause there to be a

disruption in genetic equilibrium?

• In other words what five things cause

there to be evolution?

11. What is speciation?

• The process of

species formation

which results in

closely related

species.

12. What causes speciation?

• Geographic Isolation – the physical

separation of members of a population. e.g. Death Valley pupfish

Grand Canyon squirrels

12. What causes speciation?

• Reproductive Isolation – results from

barriers to successful breeding

between population groups in the same

area. e.g. Frogs -

Nocturnal vs

diurnal

13. What is Hardy-Weinberg

Genetic Equilibrium?

• A theoretical state where genotype

frequencies in a population tend to remain

the same from generation to generation

unless acted on by outside influences

Hardy-Weinberg Genetic Equilibrium

• Allows us to consider what forces disrupt

genetic equilibrium.

1. Alleles remain the same

2. Individuals don’t enter or leave the

population

3. Population is large

4. Individuals mate randomly

5. Selection does not occur

• p and q represent the different allele

options;

• p = dominant allele and q = recessive

allele

• #1: p2 + 2pq + q2 = 1

• #2: p + q = 1

13. What is Hardy-Weinberg

Genetic Equilibrium?

• #1: p2 + 2pq + q2 = 1

• #2: p + q = 1

• #1: p2 + 2pq + q2 = 1

• #2: p + q = 1

• Are your earlobes attached or

unattached?

• Use equation #1 to find q.

• Use equation #2 to find p.

• If 1 out of every 2000 fruit flies has the

recessive condition of stubby wings, how

many will be homozygous (SS) for normal

wings?

• Use equation #1 to find q.

• Use equation #2 to find p.

• #1: p2 + 2pq + q2 = 1

• #2: p + q = 1

Ch 16 Population Genetics and Speciation - Home - …rhs.ramonausd.net/UserFiles/Servers/Server_129518/File...Ch 16 Population Genetics and Speciation 1. What is population genetics?

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