unit 18 bio - Variation and selection

What is variation?

Differences between individuals of the same species

What is continuous variation?

A range of phenotypes between two extremes

What are examples of continuous variation?

Body length and body mass

What is discontinuous variation?

A limited number of phenotypes with no intermediates

What are examples of discontinuous variation?

ABO blood groups, seed shape and colour in peas

What causes discontinuous variation?

Genes only

What causes continuous variation?

Both genes and the environment

What is a mutation?

A genetic change

How are new alleles formed?

By mutation

What is a gene mutation?

A random change in the base sequence of DNA

What are sources of genetic variation in populations?

Mutation, meiosis, random mating and random fertilisation

What factors increase mutation rate?

Ionising radiation and some chemicals

What is an adaptive feature?

An inherited feature that helps an organism survive and reproduce in its environment

How can adaptive features be identified?

By interpreting images or information about a species

What are hydrophytes?

Plants adapted to living in water

What are xerophytes?

Plants adapted to dry environments

How are hydrophytes adapted to their environment?

They have large air spaces for buoyancy and stomata on the upper surface

How are xerophytes adapted to their environment?

They have thick cuticles, small leaves and deep roots to reduce water loss

What is natural selection?

The process by which individuals better adapted to the environment survive and reproduce more successfully

What are the key steps of natural selection?

Variation, overproduction, struggle for survival, survival of the fittest, passing on of alleles

What is adaptation (in natural selection)?

The process by which populations become better suited to their environment over generations

How do antibiotic-resistant bacteria develop?

Through natural selection where resistant bacteria survive and reproduce

What is selective breeding?

The process where humans breed organisms for desirable traits

What are the steps in selective breeding?

Selecting individuals with desired traits, crossing them, selecting offspring with the traits

How is selective breeding used in agriculture?

To improve crop yield, disease resistance, or animal productivity

What’s the difference between natural and artificial selection?

Natural selection is driven by the environment; artificial selection is driven by human choice