Natural Selection

Question 1

Explain allele frequencies.

Answer 1

• genetic differences cause a variance in phenotype.
• the frequency of polymorphic alleles can be affected by:
• reproduction rate of various individuals in the population.
• immigration and emigration of individuals.
• genetic drift.
• bottleneck effect.
• founder effect.
• mutation of an allele.

Question 2

Explain migration and gene flow.

Answer 2

• Few populations are completely isolated from each other and generally migration takes place.
• ‘gene flow’ may occur if the migrants breed (immigrants may add new alleles to the gene pool, while emigrants may completely remove alleles)

Question 3

Explain genetic drift.

Answer 3

• Random changes within a population; our alleles are inherited at chance.
• in large populations: randomness isn’t noticeable.
• in small populations: there’s a chance that some alleles won’t be passed on and may be permanently lost.

Question 4

Explain the bottleneck effect.

Answer 4

• When the size of a population is drastically reduced and certain alleles may be lost through chance.
• often occurs from a catastrophic event.
• the expanded population can only carry the alleles that existed in the population that survived the event.

Question 5

Explain the founder effect.

Answer 5

-when a few individuals move to a new area and become isolated from a larger population.
- not all alleles from the original population will be carried on.
- the isolated population has less genetic diversity and deleterious recessive alleles may have a higher chance of coming together.

Question 6

The principle of natural selection.

Answer 6

1. Individuals show variation from one another within a population.
2. Many variations are caused by mutations in alleles and are inheritable.
3. More offspring are born than can survive to maturity and reproduce; there is a struggle for existence and only some organisms can reproduce.
4. Some individuals have traits that make them more suited to their environment than others, making them more likely to reproduce and pass on alleles.

Question 7

Define sexual selections.

Answer 7

Occurs when individual animals with certain inherited characteristics are more successful than other individuals in finding mates.

Question 8

Define the three types of selections.

Answer 8

Stabilising Selection- when an environment is unchanging, selection pressures act against deleterious alleles.
Direction Selection- leads to a change in a trait over time. Changes in the environment lead to selection pressures to favour new traits.
Disruptive Selection- operates in favour of extremes.

Question 9

Define micro and macro evolution.

Answer 9

Microevolution- the outcome of natural selection pressure shows a change in the frequency of various alleles within a population; any change in the gene pool of a population.
Macroevolution- major evolutionary changes above the species level.
- speciation and macro-evolutionary changes result from an accumulation of micro-evolutionary changes over time.