18 1 variation and natural selection

Variation refers to the differences between individuals of the same species.

False. It is discontinuous variation that results in a limited number of phenotypes with no intermediate values. Continuous variation results in a range of phenotypes.

Examples of continuous variation include:

Examples of discontinuous variation include:

The term environmental variation refers to differences in traits caused by factors in the environment, e.g.

True. Genetic and environmental factors interact with each other to produce observable traits in individuals, e.g. body mass is affected by diet and lifestyle, but there is also a large genetic component.

False. Continuous variation is caused by a combination of genetic factors and environmental factors.

True. Traits that show discontinuous variation are usually caused by genetic factors and not environmental factors.

The results of an investigation into student height variation would be plotted on a histogram; a graph with bars that touch each other and that would show a bell-shaped curve. This is because height is an example of continuous variation.

Mutations are changes to the genetic material.

True. Mutations can result in new alleles.

Factors that increase the rate of mutation include:

False. Mutations are random changes to the base sequence of a DNA molecule.

Sources of genetic variation in populations include:

An adaptive feature is an inherited feature that helps an organism to survive and reproduce in its environment.

Adaptive features of the dolphin include:

Adaptive features of a venus flytrap include:

Hydrophytes are plants adapted to live in very wet environments, e.g. aquatic plants.

Hydrophyte adaptations of the water lily include:

Xerophytes are plants that are adapted to live in very dry environments.

Xerophyte adaptations shown by the cactus include:

False. Natural selection can only occur when genetic variation is present. This is why populations with no, or limited, genetic variation are unable to adapt to changes in their environment.

The process of natural selection states that:

Adaptation is the process by which populations become more suited to their environment over many generations. It occurs as the result of natural selection.

Antibiotic resistance is the ability of bacteria to withstand the effects of an antibiotic; bacteria with resistance to a particular antibiotic are more likely to survive when they are exposed to the drug.

True. Random mutations in bacterial DNA can lead to antibiotic resistance, enabling some bacteria to survive antibiotic treatment.

Antibiotic resistant strains of bacteria can arise by natural selection as follows:

Antibiotic use can increase the probability that a resistant population of bacteria will arise because the antibiotics kill any non-resistant individuals, meaning that any randomly occurring alleles for resistance become advantageous. The resistance alleles are therefore more likely to be passed on.

The selective breeding process involves:

The purpose of selective breeding is to improve the yield from crops and domesticated animals.

Features that might be selectively bred for in plants include:

Features that might be selectively bred for in animals include:

Natural and artificial selection are different as follows: