Mechanisms of Evolution

Question 1

Gene pool

Answer 1

total of all alleles within the population

Question 2

Allele frequency

Answer 2

The % of each allele of a given gene in population (allele frequency) determines the genetic characteristic of that population.

Question 3

Microevolution

Answer 3

Changing percentages or frequencies of alleles within populations leads to evolution within a population

Question 4

Mutation

Answer 4

• Description: mutation randomly introduces new alleles into a population.
• Effect: Mutation changes allele frequencies.
• Mutation is a change in the DNA of an individual.
• If it affects body cells cannot be inherited
• If it affects sex cells (gametes) inheritable
• A heritable mutation has the potential to affect an entire gene pool
• Inheritable mutations can either be: neutral, harmful or beneficial to the individual’s fitness.

Question 5

Gene flow (or migration)

Answer 5

• Description: Gene flow occurs between two different interbreeding populations that have different allele frequencies.
• Effect: Gene flow may change allele frequencies in either or both populations through a “flow”, or movement, of genes (alleles).
• When individuals move from one population to another, they alter the allele frequency of both populations.
  Gene flow: the net movement of alleles from one population to another as a result of migration of the individuals
  Ex: gray wolf travels many km in search of new territory, it mates with a member of a nearby population bringing a new allele to the gene pool therefore genetic diversity in nearby population may increase

Question 6

Non-random mating

Answer 6

• Description: During non-random mating, individuals in a population select mates, often on the basis of their phenotypes
• Effect: Non-random mating increases the proportion of homozygous individuals in a population, but does not affect the frequencies of alleles.
• Mating among individuals on the basis of mate selection for a particular phenotype or due to inbreeding
  1. Preferred phenotypes: choosing mates based on physical and behavioural traits
• It prevents individuals with certain phenotypes from mating and only individuals that mate contribute to the gene pool
  2. Inbreeding: closely related individuals breed together.
• Homozygous genotypes become more common. - - - - Harmful recessive alleles are more likely to be expressed.
• Pure bred animals have a higher incidence of deformities and health problems (low fertility, die young)

Question 7

Genetic drift

Answer 7

• Description: Refers to the random change in genetic variation from generation to generation due to chance.
• Effect: Genetic drift changes frequencies of alleles.
  Genetic drift: change in frequency of alleles due to chance events in a breeding population
• Genetic drift has greatest effect on smaller populations
• The smaller the population the less likely it is too see the parent gene pool in the next generation

Question 8

Natural selection

Answer 8

• Description: Natural selection is the result of the environment selecting for individuals in a population with certain traits that make them better suited to survive and reproduce than others in a population.
• Effect: Over many generations, frequencies of alleles of many different genes may change, resulting in significant changes in the characteristics of a population.
• Environment selecting for individuals in a population with certain traits that make them better able to survive & reproduce.
• There are 3 types of natural selection that affects the frequency of a heritable trait in a population
  Stabilizing selection, directional selection & disruptive selection

Question 9

Founder effect

Answer 9

• Effect: a change in gene pool that results when a few individuals start a new isolated population
• These “founders” carry some but not all alleles from the original population’s gene pool which means diversity of new population is limited
• This is usually seen in island populations
  Ex: The Amish population of Philadelphia, PA was found in the 1700s by only a few families. Now the population has an unusually high frequency of polydactylism (presence of 6th finger or toe)

Question 10

Bottleneck effect

Answer 10

• Effect: changes in gene distribution that results from a rapid decrease in population size
• Things like starvation disease and natural disasters can severely reduce the size of a population
• Survivors only have a few of the various alleles that were present before in the larger population so now the gene pool now has less diversity

Question 11

Stabilizing Selection

Answer 11

• favours an intermediate phenotype and selects against extreme variants of the phenotype
  Ex weight of human babies

Question 12

Directional Selection

Answer 12

• favours phenotypes at one extreme over the other
• This type of selection is common during times of environmental change
  Ex: colour of pepper moths or antibiotic resistant bacteria

Question 13

Disruptive Selection

Answer 13

• favours extreme phenotypes rather than intermediate phenotypes
• Sometimes intermediate phenotypes are completely eliminated from the population
  Ex: Male coho salmon -> Very large phenotypes (4500 grams or more) are better at fighting for access to females’ eggs and very small phenotypes (~ 500 grams) are better at “sneaking” & fertilizing females’ eggs.