Evolution and Populations

Question 1

What is microevolution?

Answer 1

Microevolution is the change of allele frequencies of a population over generations.

Question 2

What is a population?

Answer 2

A population is an interbreeding group of individuals that occupy a geographic area

Question 3

What is a gene pool?

Answer 3

A gene pool is all the genes available for reproduction in a population

Question 4

How do populations, evolution, and individuals relate?

Answer 4

A population evolves, not individuals. However, natural selection acts on the individual. Their death or reproduction affects the populations gene pool

Question 5

What creates the genetic variation that makes evolution possible?

Answer 5

Sexual reproduction and mutations produce the genetic variation that makes evolution possible
- Most genetic variations are NOT due to mutations, but due to sexual recombination of alleles already in the population.

Question 6

What is a morph?

Answer 6

A morph is two or more forms of a phenotypic characteristic in a population

• A population is said to be polymorphic for a characteristic if two or more morphs are found in noticeable numbers
• Ex: Freckles in humans

Question 7

What is a polymorphic characteristic?

Answer 7

A polymorphic characteristic is two or more phenotypes for a given trait in a population at noticeable levels. Allows for diversity or variation of a populations gene pool.

• Ex: White vs red petals
• Ex: ABO blood type

Question 8

What is heterozygote advantage?

Answer 8

Heterozygote advantage occurs when the heterozygote has better fitness than a homozygote of either allele.
- Ex: Sickle cell heterozygote and decreased malaria fatality

Question 9

What is Frequency-Dependent Selection?

Answer 9

Frequency-Dependent Selection: The survival and reproduction rates decline for a morph as it increases in phenotype frequency.
- Ex: As a butterfly color morph is rare, birds won’t know to target it, as it becomes more prominent, birds will selectively target it and it will give rise to different morphs to become prominent.

Question 10

What is geographic variation?

Answer 10

Geographic variation occurs when the geography over a given area selects for different phenotypes or genotypes of similar or the same species.

• Rabbits with whiter fur up on the snowy mountain top vs brown rabbits down at the base.
• This is where we see ecoclines (clines for short)

Question 11

What is an Ecocline (cline)?

Answer 11

An Ecocline, or cline for short, consists of forms of species that show gradual phenotypic and/or genetic differences over a geographical area.
- Rabbits with white fur in the snowy north and rabbits with brown fur in the drier south.

Question 12

What is the Hardy-Weinberg principle?

Answer 12

The Hardy-Weinberg principle states that the genotypes and allele frequency of a given population will remain constant from one generation to another, providing that only Mendelian genetics and recombination of alleles operate.

Question 13

What are the five Hardy-Weinberg conditions?

Answer 13

The five Hardy-Weinberg conditions are:

1) Large Population: Gene frequency doesn’t change as a result of chance alone
2) Random Mating: Inbreeding causes little mixing of genes
3) No Mutations: A mutation modifies our gene pool
4) No Natural Selection: Survival differences can alter gene frequencies
5) No Gene Flow: No immigration, no emigration, no pollen transfer (If a strong wind blew from point A to point B, pollen can transfer. We don’t want this. If a population had an influx of new members this would also be disrupted)

NB. No natural population meets these criteria, so any time a population deviates from this, they are inviting evolutionary change.

Question 14

What are the Hardy-Weinberg Equations?

Answer 14

The Hardy-Weinberg Equations:

p + q = 1
p = frequency of dominant allele
q = frequency of recessive allele

p^2 + 2pq + q^2 = 1
p^2 = frequency of dominant homozygous genotype
2pq = frequency of heterozygous genotype
q^2 = frequency of recessive homozygous genotype

Question 15

What three mechanisms operate to alter allele frequencies directly and cause the most evolutionary change?

Answer 15

The three mechanisms that cause the most evolutionary change to allele frequencies are:

• Natural Selection: Fittest survive
• Gene Flow: Alleles are moved by fertile individuals from one population to another
• Genetic Drift: Loss of alleles in a small population

Question 16

What is genetic drift?

Answer 16

Genetic drift is the change to the alleles in a small population when certain alleles aren’t passed on due to the carriers dying off or not reproducing.

• This negates natural selection and instead alleles that may have been rare once can become common. These genes that are more common aren’t necessarily good.
• Reduces genetic variation

Question 17

What is gene flow?

Answer 17

Gene flow is when alleles are carried by fertile individuals from one population to another.

Question 18

What are founder effects?

Answer 18

Founder effects is a type of genetic drift. It occurs when a few members of a parent population migrate to a new area. The small gene pool interbreeds and genetic drift occurs

Question 19

What is a bottleneck?

Answer 19

A bottleneck is a type of genetic drift. Some bad event occurs that significantly reduces the population. The small population may have some alleles that are over or underrepresentative of the original population, due to chance alone.

Question 20

What is fitness?

Answer 20

Fitness is the contribution that an organism makes to the gene pool of the next generation.

Question 21

What is Darwinian fitness?

Answer 21

In a population, it is the number of fertile offspring produced by an individual

Question 22

What is stabilizing selection?

Answer 22

Stabilizing selection is when the alleles that produced uncommon phenotypes are eliminated over time.

• This tends to undo the effects of gene flow, mutation, or genetic drift.
• Ex: Babies smaller or larger than the range of 6.5-9 pounds often die
• Ex: Robins usually only lay four eggs per season. More eggs would be bad, as it would be harder for the robin to feed all the kids and they may all die. Less would be bad because it may not bring about enough healthy birds to reach sexual maturity.

Question 23

What is directional selection?

Answer 23

Directional selection is when allele frequencies shift due to changing conditions in the environment

• Ex: Peppered moth in England. Light gray used to be the most dominant color. As pollution occurred and the landscape became darker, the moth became darker too. The allele frequencies of the population changed
• Ex: Insecticide Resistance. 99% of the insects are killed off, but the 1% that have genetics allowing them to survive reproduce. The new generation will have a significantly higher % of insecticide resistance

Question 24

What is disruptive selection?

Answer 24

Disruptive selection occurs when individuals with either extreme variation of a trait have higher survivability than the intermediate.

• Ex: In a landscape of stark white and stark black rocks, only the white and black rabbits survive. The gray ones die off.
• Ex: Birds with long beaks can open fruits to get to seeds, while short squat ones can break open nuts to get to seeds. Those with average beaks can do neither and die.

Question 25

What is sexual dimorphism?

Answer 25

Sexual dimorphism is differences between a male and a females appearance. They could differ in:

• Size
• Color
• Behavior
• Outward appearance

Birds like ducks and peacocks are a good example of this.

Question 26

What is sexual selection?

Answer 26

Sexual selection is a special type of natural selection where traits that help you find a mate are selected for.

• Gives rise to sexual dimorphism
• A trait like brightly colored feathers may help you attract a mate, but it will also attract predators to you. Sexual selection ensures its passed on, although it may not be the safest trait in regards to survival

Question 27

What is diploidy? How does it counter selection?

Answer 27

Diploidy is the fact that we have two forms of each allele. The fact that recessive alleles can be hidden in heterozygotes, allows the recessive alleles to survive. If circumstances change, it will allow the recessive allele to be selected for if it becomes competitive again.

Question 28

What is Heterozygote advantage?

Answer 28

Heterozygote advantage is when the heterozygote is the fittest against the homozygotes.
- This allows the recessive genes to continue being passed on

Question 29

What is neutral variation?

Answer 29

Neutral variation is the variation in alleles that have a neutral impact on the fitness of an organism

• These tend to accumulate in a population becuase they are never selected against.
• These alleles may increase or decrease as a result of genetic drift
• Ex: eye color or fingerprint variation