Unit 5.2: Natural Selection

Question 1

What is directional selection?

Answer 1

Directional selection is a mode of natural selection in which selection favors one end of the range with a progressive change in population in that direction. Often occurs in isolated populations of a species.

Question 2

What is disruptive selection?

Answer 2

Disruptive selection is a mode of natural selection in which extreme types are selected and adapt to different niches. Reproductive barriers become established between extreme types

Question 3

List 3 sources of variation among individuals of a species.

Answer 3

1. Mutations, which produce new alleles and expand the gene pool.
2. Independent assortment and crossing-over during Meiosis. Indie. assortment leads to new combinations of chromosomes. Crossing over creates new combinations of alleles.
3. Sexual reproduction, which combines alleles from two different individuals. Mutations can be brought together through sexual reproduction.

Question 4

What is overpopulation? What are some of its consequences?

Answer 4

Overpopulation occurs when populations produce more offspring than the environment can/will support.
Consequences:
-When the carrying capacity is exceeded, members of the population must compete for resources, because they become increasingly scarce.

Question 5

Define an adaptation.

Answer 5

An adaptation is a characteristic developed by natural selection that makes an animal more suited to its environment.

Question 6

What are the results of adaptation?

Answer 6

Adaptations give certain members of the population an advantage and enable them to live longer and have more offspring, which also inherit the adaptation and give them a greater chance of surviving and carrying on the population by reproducing.
-There is progressive change as useful alleles become more frequent. This results in evolution, a cumulative change in heritable characteristics.

Question 7

Describe bacterial resistance.

Answer 7

Bacteria reproduce quickly, so more mutations appear, leading to more variation. If a form of bacteria inherits a mutation that makes it resistant to antibiotics, the resistant form survives against the antibiotics. It has no competition and will continue to reproduce, passing on the resistant allele to offspring.

• Bacteria can also pass genes to other bacteria species through plasmids.
• The frequency of the resistant allele in the gene pool increases.