8.1 Microevolution

Question 1

Describe a gene pool

Answer 1

-All the alleles in the individuals that make up a population
-The reservoir for the next generation to get its genes
-Where “Genetic Variation” exists

E.g. wild mustangs

Question 2

List two sources of variation

Answer 2

mutation and sexual reproduction

Question 3

Describe a mutation

Answer 3

-Change in DNA sequence
-Due to mistakes or environment
-Some don’t change phenotype
-Affects organisms’ fitness

Question 4

Describe sexual reproduction

Answer 4

-Variation due to scrambling of alleles
-Differences among individuals due to sexual recombination

(i.e. meiosis)

Question 5

Describe the Hardy-Weinburg Equilibrium concept

Answer 5

-Population NOT undergoing change to their gene pool
-Therefore, NOT EVOLVING
-Frequency of alleles in gene pool are constant
-Population rarely remains long in H-W Eq. in nature

Question 6

What are the 2 equations used in the H-W Equilibrium?

Answer 6

p (squared) + 2pq + q (squared) = 1

p + q =1

Question 7

What does the p mean in the H-W Equilibrium?

Answer 7

Homozygous dominant (AA)

Question 8

What does the q mean in the H-W Equilibrium?

Answer 8

Homozygous recessive (aa)

Question 9

What does the pq mean in the H-W Equilibrium?

Answer 9

Heterozygous (Aa)

Question 10

For a population to be in Hardy-Weinberg Equilibrium there MUST BE…

Answer 10

1. Random Mating
2. Large Population
3. No movement in/out of the population (NO gene flow)
4. No mutations
5. No Natural Selection

Question 11

Describe microevolution

Answer 11

Generation-to-generation change in freq. of alleles in a population

-occurs if any conditions of H-W Eq. are NOT MET
-small scale evolution

Question 12

Mechanisms of microevolution

Answer 12

-Natural Selection
-Sexual Selection
-Artificial Selection
-Genetic Drift
-Gene Flow

Question 13

Describe Natural Selection

Answer 13

-Is NOT random
-Environment increases frequency of alleles that provide reproductive advantages to individuals

-Therefore, leading to evolution of adaptations
-3 Types of Selective Pressure that can account for
Natural Selection:
- Stabilizing Selection
- Directional Selection
- Disruptive Selection

Question 14

What is Stabilizing Selection

Answer 14

Individuals near the centre of the phenotypic range are selected for

Question 15

What is Directional Selection

Answer 15

Individuals near one end of the phenotypic range are selected for

Question 16

What is Disruptive Selection

Answer 16

-Individuals at the upper and lower ends of the phenotypic range are selected for
-May lead to 2 distinct phenotypes in the population

Question 17

Describe Sexual Selection

Answer 17

-Form of Natural Selection in which individuals with certain traits are more likely to obtain mates than others
-Mating is often NOT RANDOM

Examples…
Male peacocks with elaborate tails evolved because females preferred to reproduce with those males
Longer tailed male widow birds are more successful at reproduction

Question 18

Describe Artificial Selection

Answer 18

-Intentional breeding to produce certain traits
-Darwin used as evidence of Natural Selection
-Is a mechanism of Microevolution
-Results in DECREASED genetic variability

Example…
Impressive was a fast horse chose for breeding
Unfortunately, descendants have Hyperkalemic Periodic Paralysis (HYPP) disorder

Question 19

Describe Genetic Drift

Answer 19

-Unlike Artificial Selection and Natural Selection, Genetic Drift is RANDOM!

-Change in gene pool due to chance

-Has a huge effect on a small population

2 types:
Bottleneck Effect
Founder Effect

Question 20

What is the Bottleneck Effect

Answer 20

-Disasters reduce the size of a population

-Therefore, reduce gene pool

-Survivor alleles represented more frequently

-Therefore decreased genetic variation

-Loss of variation results in a decreased ability of a population to adapt to environment change because of such small numbers

E.g. cheetah

Question 21

What is the Founder Effect

Answer 21

-Few individuals colonize an isolated island, lake, etc.

-Genetic Drift in a new colony changes allele frequencies due to the genetic makeup of the founders of the colony

-The smaller the colony, the less its genetic makeup will represent the gene pool of the larger population from which the colonists came

E.g. Darwin’s finches & Afrikaner population in South Africa

Question 22

Describe Gene Flow

Answer 22

-RANDOM

-Exchange alleles with another population

-Occurs when fertile individuals or gametes migrate between populations

-Disrupts H-W Eq.

-Decreases genetic difference between populations

-If strong enough, can mix neighbouring populations into a single population with a common gene pool

Question 23

In genetic terms, what indicates that
microevolution is occurring?

Answer 23

-a change in gene frequency within a population
-evolution at this scale can be observed over short periods of time, such as from one generation to the next

Question 24

Define the terms “allele” and “gene pool.”

Answer 24

allele- alternative version of a gene

gene pool- consists of all the alleles in all
the individuals that make up a population

Question 25

Which source of variation brings more diversity into a gene pool of a sexually reproducing species?
Explain.

Answer 25

Sexual Reproduction
-In sexually reproducing organisms, variation due to the scrambling of existing alleles, including those that originated as mutations in earlier generations
-each offspring receives a new combination of alleles

Question 26

Which source of variation brings diversity into a gene pool of asexually reproducing species?

Answer 26

Mutation
-some change an organism’s phenotype
-can have an effect on an organism’s fitness in
the environment
-especially important as a source of variation in
ASEXUALLY reproducing organisms that clone themselves rapidly, such as bacteria

Question 27

How are pesticide-resistant insects an example
of natural selection?

Answer 27

Directional selection

• By spraying crops with poisons to kill insect pests, humans have favoured the reproduction of insects with inherited resistance to the poisons over those with no resistance.

-Most survivors of the first pesticide treatments were insects with genes that somehow enabled them to resist the chemical attack.
-Their offspring inherited the genes for pesticide resistance.
-In each generation, the percentage of
pesticide-resistant individuals in the insect population increased.
-The population underwent directional selection.
-The alleles that produce higher pesticide resistance increase in the population

Question 28

What are the three patterns of natural selection

Answer 28

stabilizing(centre chosen), directional(one end chosen) and disruptive selection(both ends chosen)

Question 29

Which pattern of natural selection is most likely to lead to two distinct phenotypes? Explain

Answer 29

Disruptive selection
-takes place when individuals at the upper and lower ends of the range of phenotypes are favoured
-may lead to the rise of two distinct phenotypes within a population because 2 phenotypes are favoured by the environment

Question 30

What is another name for disruptive selection?

Answer 30

diversifying selection

Question 31

Under what circumstances is Hardy-Weinberg
equilibrium disrupted?

Answer 31

Several factors may disrupt Hardy-Weinberg equilibrium, or in other words, cause microevolution.

These include natural selection, sexual
selection, artificial selection, genetic drift, and gene flow.

Question 32

Describe what can happen to a gene pool as a
result of the bottleneck effect.

Answer 32

Disasters such as earthquakes, floods, droughts, and fires may drastically reduce the size of a population, which also reduces the size of its gene
pool

Question 33

Explain the concept of sexual selection and
provide an example

Answer 33

-form of natural selection in which individuals with certain inherited traits are more likely to obtain mates than other individuals.
-in sexual selection, other individuals of the same species screen the traits

e.g.
-in widow birds, females pick males with long tails
-male peacocks with elaborate tails evolved because females preferred to reproduce with those males

Question 34

Give an example of directional selection

Answer 34

Peppered Moths
-light-coloured peppered moths are better camouflaged against a pristine environment; likewise, dark-coloured peppered moths are better camouflaged against a sooty environment
-as the Industrial Revolution progressed, the colour of the moth population shifted from light to dark

dark-coloured moths were favoured by the environment

Question 35

Give an example of disruptive selection

Answer 35

Rabbits
-grey and himalayan (grey+white) rabbits are better able to blend with a rocky environment than white rabbits, resulting in diversifying selection

grey and himalayan were favoured over white by the environment

Question 36

Give an example of stabilizing selection

Answer 36

Robins
-robins typically lay four eggs, larger amounts of eggs may result in malnourished chicks, while smaller amounts of eggs may result in no viable offspring

4 eggs were favoured over any other amount of eggs by the environment

Question 37

Suppose a recessive allele causes a disease
that usually kills the animal before it can
reproduce.
(a) Predict what will happen to the frequency
of that allele in the population.
(b) What type of selection will occur? Explain

Answer 37

a) lesser frequency of recessive alleles in the population

b) disruptive selection because animals need 2 copies of the recessive allele, so the animals will favour animals carrying heterozygous alleles and homozygous dominant alleles.

Question 38

For each of the following situations, predict
whether the Hardy-Weinberg equilibrium
would be maintained after several generations.
Explain your reasoning.
(a) A population of long-tailed widow birds is
maintained at a local zoo

Answer 38

it would not be maintained because sexual selection disrupts the equilibrium

female widow birds favour males with long-tails and would mate with them= sexual selection

Question 39

For each of the following situations, predict
whether the Hardy-Weinberg equilibrium
would be maintained after several generations.
Explain your reasoning.
(b) A population of birds lives on an isolated
island.

Answer 39

yes because this follows the conditions for the equilibrium to be maintained which are:

1. Random Mating
2. Large Population
3. No movement in/out of the population (NO gene flow)
4. No mutations
5. No Natural Selection

Question 40

For each of the following situations, predict
whether the Hardy-Weinberg equilibrium
would be maintained after several generations.
Explain your reasoning.
(c) Climate change is melting the polar ice
where polar bears live

Answer 40

no it would not be maintained because genetic drift disrupts the equilibrium

-this would be an example of the bottleneck effect and would reduce the size of the polar bear population = eq. disrupted
-it needs to be a large population for the equilibrium to be maintained

Question 41

For each of the following situations, predict
whether the Hardy-Weinberg equilibrium
would be maintained after several generations.
Explain your reasoning.
(d) A rat population lives in the subway system
in Toronto.

Answer 41

no it would not be maintained because one of the conditions required for the equilibrium is that there is NO movement in or out of the population and there can’t be a small population

-it would be disrupted because the rats would get stepped on or killed, which would cause movement out of the population and would reduce the size of their population

Question 42

The female peacock is less colourful and has
a shorter tail than the male, pictured below.
Explain, in evolutionary terms, the advantage
that the bright colouration and elaborate tail
feathers give the male

Answer 42

sexual selection
-the advantage is that the females will be more attracted to those males and will mate with them

Question 43

Suppose a population of caribou leaves its herd
and migrates to a new area where there are no
natural predators. Hypothesize the effect this
situation might have on the original population
and on the founding population

Answer 43

effect on original population
-decrease in size
-less genetic variation
-decreased ability of a population to adapt to their environment because of such small numbers

effect on founding population
-changes allele frequencies due to the genetic makeup of the founders of the colony
-more of the new population because there are fewer predators

Question 44

Many individuals with sickle-cell disease in
North America are of African descent. Explain
this phenomenon. Predict what should happen
to the frequency of the sickle-cell allele in
North America over time

Answer 44

-in some African populations, it affects about one in 25 individuals, so they are more likely to have the disease

-if they have offspring with North Americans, the frequency of the sickle-cell allele will be more frequent in our population because the alleles from the people of African descent will pass to their offspring

Question 45

Which of the conditions that maintain
Hardy-Weinberg equilibrium does each of the
five mechanisms of microevolution upset?

Answer 45

Sexual Selection would disrupt Random Mating

Genetic Drift would disrupt a Large Population

Gene flow would disrupt No movement in/out of the population

Artificial Selection would disrupt No mutations

Natural Selection would disrupt No Natural Selection

Question 46

Choose one mechanism of microevolution and
explain how human activity has affected a
particular species in this manner.

Answer 46

gene flow
-when people cut down forests and destroy habitats to build houses, it causes animals to have to migrate to a different place which will cause them to mate with other animals of the same species (interbreeding)