Microevolution Random Events

Question 1

Hardy Weinberg Principle

Answer 1

A principle that states that allele frequency will stay the same as long as…
1) The population remains large
2) Mating opportunities are equal
3) No mutations occur
4) No migrations occur
5) No natural selection
→ It gives a baseline to compare actual allele frequencies to

Taking this into account evolution can be defined as the change in allele frequency

Question 2

Mutations

Answer 2

→ Ultimate source of all variation
→ all mutations are random changes to DNA
↪ May be a result of unrepaired changes in DNA sequences or chromosome breakage. (DNA replication failing during Synthesis, Meiosis mutations, mutagens)
→ They are the only source of additional genetic material and new alleles.
→ Can be passed to later generations only if the mutation is in the gamete (mutations in somatic cells are not passed on)

Question 3

3 Types of Mutations

Answer 3

Neutral Mutation: has no immediate effect on an individual’s fitness. Most are silent mutations.

Harmful Mutation: Inheritable change in a cell’s DNA that impairs the proper operation of a gene product or regulatory function.
↪ Decreases fitness, therefore natural selections selects against

Beneficial Mutation: gives individual selective advantage 🡪 increased reproductive success
↪ Increases fitness, therefore natural selection selects for the mutation

Question 4

Genetic Drift

Answer 4

Changes in allele frequency due to chance
↪ Not natural selection
↪ E.g. when a natural disaster strikes and many individuals die (who survives wasn’t more fit to survive a natural disaster - it was by chance)
The alleles present in the survivors are only a (random) sample of those of the original population

→ Because genetic drift alters the distribution of variants in a population, it is still a mechanism that drives evolution, but it doesn’t work to produce adaptations.
→ Genetic drift occurs in all populations of non-infinite size, but its effects are strongest in small populations.

Question 5

Genetic Drift: Allele Fixation

Answer 5

→ Genetic Drift tends (doesn’t have to) to ‘fix’ alleles (Allele Fixation), meaning that there is only one allele left and the allele frequency is 100%
↪ As a result, it reduces genetic frequency

Question 6

Genetic Drift: Bottleneck Effect

Answer 6

A dramatic, often temporary, reduction in population size
→ Only a small sample of alleles survives to establish the new population
↪These individuals often do not reflect the allele makeup of the original population, and because of that, genetic drift often results

Ex: Poaching is a bottleneck effect

Question 7

Genetic Drift: Founder Effect

Answer 7

Results after a small portion of a population isolate themselves and create a new population.
↪ The distribution of variation for a trait will likely not be the same as the original population.

Question 8

Gene Flow

Answer 8

The movement of alleles from one population to another
↪ Permanent Migration
↪ Mating between populations without permanent migration.
→ Genetic info is shared between populations
→ Unlike genetic drift, gene flow reduces genetic differences between populations
↪ New alleles possibly introduced into one population
↪ Alleles potentially lost from another population