Adaptations and variation

Variation

Differences between individuals of the same species

Inherited variation

Differences caused by genes passed from parents

Environmental variation

Differences caused by surroundings such as diet, climate or lifestyle

How inherited variation is caused

Different alleles, gene mixing in fertilisation, mutations

How environmental variation is caused

Climate, diet, lifestyle, experiences

Where information is stored in cells

DNA inside chromosomes in the nucleus

Number of human chromosomes

46 chromosomes (23 pairs)

What fossils are

Preserved remains or traces of ancient organisms

How fossils are formed

Organism dies → buried → soft parts decay → minerals replace bones → fossil forms

Limitation of fossil record

Incomplete because soft organisms decay, fossils are destroyed, not all fossils found

Selective breeding

Humans choosing parents with desired traits to produce offspring with those traits

How selective breeding produces desired characteristics

Parents with chosen traits pass their alleles to offspring

Genetic engineering

Direct modification of an organism’s DNA using biotechnology

Variation in a population

Differences caused by inherited and environmental factors

Adaptations

Features that help organisms survive in their environment

How adaptations arise

Useful variations from mutations become common through natural selection

Natural selection

Individuals with advantageous traits survive and reproduce, passing on beneficial alleles

Competition in animals

Animals compete for food, water, mates, territory

Competition in plants

Plants compete for light, water, space, minerals

Adaptations for hot environments

Large ears, thin fur, nocturnal, water storage

Adaptations for cold environments

Thick fur, blubber, small extremities, white fur

Punnett square

Diagram used to predict probability of inheriting traits

Symptoms of cystic fibrosis

Thick mucus, breathing difficulty, digestive problems

Symptoms of sickle cell anaemia

Painful episodes, fatigue, infections, sickle-shaped blood cells

Symptoms of Huntington’s disease

Mood changes, memory decline, uncontrollable movements

Continuous variation

Range of values with no distinct categories (e.g., height)

Discontinuous variation

Clear categories with no in-between values (e.g., blood group)

Data collection for variation

Gather measurements, organise into tables and graphs, analyse patterns