Chapter 17: Selection and evolution

Question 1

Discontinuous variation

Answer 1

• Specific intermediate
• Linked gene -> advantageous
• Are entirely genetically controlled, cannot be altered by external conditions
• Bar chart represents data
• Different alleles at a single locus have large effects on the phenotype.
• Different genes have quite different effects on the phenotype.

Question 2

Continuous variation

Answer 2

• There are many intermediates between the extremes.
• Under genetic control but there are several pairs of genes involved.
• Environment
• Normal distribution
• Different genes have the same, sometimes additive effect on the phenotype.
• A large number of genes may have a combined effect on a particular phenotypic trait
• Different alleles at a single locus have small effects on the phenotype.

Question 3

Natural selection

Answer 3

the way in which individuals with particular characteristics have a greater chance of survival than individuals with out those characteristics, and are therefore more likely to breed and pass on the genes for these characteristics to their offspring.

Question 4

Why natural selection occurs

Answer 4

All species have the reproductive potential to increase the sizes of their population, environmental factors come into play to limit population growth.
-> Decrease the rate of reproduction or increase the rate of mortality so that many individuals die before reaching reproductive age.

Question 5

Biotic factor

Answer 5

caused by other living organisms

- predator, competition for food, infection by pathogens

Question 6

Abiotic factor

Answer 6

caused by non-living components of the environment

- water supply or nutrient levels in the soil

Question 7

Selection pressure

Answer 7

an environmental factor that confers greater chances of survival and reproduction on some individuals than on others in a population

Question 8

Stabilising selection

Answer 8

Natural selection keeps allele frequencies as they are

Question 9

Directional selection

Answer 9

If environmental factors that exert selection pressures change, or if new alleles appear in a population, then natural selection may cause a change in the frequencies of allele.

Question 10

Evolution occurs

Answer 10

Over many generations, directional selection may produce large changes in allele frequencies.

Question 11

Genetic drift

Answer 11

A change in allele frequency that occurs by chance, because only some of the organisms of each generation reproduce.
- most noticeable when a small number of individuals are separated from the rest of a large population

Question 12

The Hardy-Weinberg principle

Answer 12

p + q = 1

p^2 + 2pq + q^2 = 1

Question 13

Hardy-Weinberg principle is not applied when:

Answer 13

• the population is small
• significant selective pressure against one of the genotypes
• migration of individuals carrying one of the two alleles into, or out of, the population.
• non-random mating

Question 14

Artificial selection

Answer 14

When humans purposefully apply selection pressures to populations

Question 15

Selective breeding

Answer 15

• individuals showing one or more of desired features to a larger degree than other individuals are chosen for breeding.
• some of the alleles conferring these characteristics increase in frequency.
• repeat this for generations

Question 16

The Darwin-Wallace theory of evolution by natural selection

Answer 16

• Observation:
  1. Organisms produce more offspring than are needed to replace the parents.
  2. Natural populations tend to remain stable in size over long periods.
• > Deduction 1: There is competition for survival
  3. There is variation among the individuals of a given species.
• > Deduction 2: The best adapted variants will be selected for by the natural conditions operating at the time.