Variation and Selection

Vocabulary flashcards covering variation, mutations, natural selection, and artificial selection based on the lecture notes.

Variation

The differences in characteristics that exist between individuals belonging to the same population or species.

Continuous Variation

A type of variation that exhibits many intermediate characteristics across a wide range of individuals, producing a normal distribution curve when graphed.

Discontinuous Variation

A type of variation featuring sharply contrasting characteristics with no intermediate forms, which is easily distinguished and typically represented in a bar graph.

Mutations

Spontaneous changes in chromosomes or genes that cause them to code for a different characteristic, introducing new genes into a gene pool.

Mutagens

Environmental agents—such as ultraviolet light, high energy radiations, cyclamates, and formaldehyde—that significantly increase the rate of mutation.

Gene Mutation

A change in the sequence of base pairs in a DNA molecule, causing it to code for a different protein or characteristic.

Sickle Cell Anaemia

A genetic condition caused by a gene mutation in haemoglobin, causing red blood cells to become rigid and sickle-shaped under low oxygen levels, leading to capillary blockages and a reduced lifespan of red blood cells.

Sickle Cell Genotypes

The genetic combinations displaying incomplete dominance: $H^S H^S$ (not anaemic), $H^S H^s$ (sickle cell trait), and $H^s H^s$ (anaemic).

Haemophilia

A hereditary disorder caused by a mutant recessive allele found on the X chromosome, causing blood to lack necessary blood clotting factors.

Chromosome Mutation

A change in the number and size of chromosomes resulting from abnormal chromosome behavior during meiosis, which alters the phenotype.

Down Syndrome

A human condition caused by a chromosome mutation where chromosome $21$ fails to separate during anaphase in ovum formation, producing a zygote with $47$ chromosomes instead of $46$.

Natural Selection

The process of competition for existence where individuals better adapted to their environment have an increased chance of survival and reproduction, while poorly adapted individuals die off.

Charles Darwin's Theory of Evolution

A theory proposing that existing species colonising isolated habitats develop adapted characteristics through natural selection over millions of years, leading to the formation of new species.

Peppered Moth Natural Selection

An example of natural selection where dark-coloured peppered moths were selected for after the industrial revolution because they were camouflaged against soot-blackened tree trunks, while light-coloured moths were preyed upon by birds.

Artificial Selection

The process where human beings deliberately choose and interbreed individual plants or animals with desirable characteristics so those genes remain in the population.

In-breeding

Artificial selection involving the crossing of closely related individuals within a species (such as self-pollination in crop plants or breeding pedigree dogs) to maintain parental characteristics.

Out-breeding

Artificial selection involving the crossing of unrelated species or strains, such as crossing wild grass with wheat to produce disease-resistant hybrid varieties.

Gene Pool

The total number of alleles or versions of genes present within a species or population.

Disadvantages of Inbreeding

Processes that reduce the gene pool—making populations vulnerable to extinction from new diseases—and increase the chance of inheriting physical defects or genetic diseases.