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any chromosome that is not a sex chromosome

Back Cross

The individual with the unknown genotype is bred with a homozygous recessive individual. (test cross)

Continuous Variation

Variation measured on a continuum rather than in discrete units or categories (eg height in human beings).

Crossing Over

the interchange of sections between pairing homologous chromosomes during the prophase of meiosis

Dihybrid inheritance

Considers 2 different alleles from each parent

discontinuous variation

characteristics that have either one phenotype or another eg. tongue rolling, eye colour etc.

Dominant Allele

an allele whose trait always shows up in the organism when the allele is present

gametic mutation

A mutation in the sex cells. Can be inherited.


genetic makeup of an organism

independant assortment

the process of random segregation and assortment of chromosomes

law of segregation

members of a pair of homologous chromosomes separate during the formation of gametes and are distributed to different gametes so that every gamete receives only one member of the pair


cell divison that produces gametes

monohybrid inheritance

inheritance of a single trait, controlled by alleles of a single gene


any agent (physical or environmental) that can induce a genetic mutation or can increase the rate of mutation. (mutagens are, ionising radiation, viruses & microbes, environmental poisons, alcolol and diet.)


a permanent change in the genetic code.


The physical expression of a gene

recessive allele

an allele that is masked when a dominant allele is present


The alternate form of a gene


the exchange of alleles between homologous chromosomes.

sex chromosome

chromosomes that code for gender (XX =female XY=male)

somatic mutation

mutation in body cells. These can not be inherited

test cross

The individual with the unknown genotyoe is bred with a homozygous recessive individual. (back cross)


any difference between individuals of the same species

Gene mutations

Mutations that produce changes in a single gene

Chromosome Mutations

Either changes in structure of a chromosome or the loss of an entire chromosome

mate selection

Individuals select for desired phenotypes in mates. (prefereble traits will become more common in the gene pool)

Significance of meiosis

ensures that offspring have the correct amount of chromosomes in the somatic cells

Stages of Meiosis

interphase, prophase1, metaphase1, anaphase1, telophase1, prophase2, metaphase2, anaphase2, telophase2,


term used to refer to an organism that has two different alleles for the same trait eg Bb


term used to refer to an organism that has the same alleles for one trait, having two identical alleles for a trait eg BB, bb


a genetically determind characterisitc.


the change in an organism over time


inherited characteristic that increases an organism's chance of survival

allele frequency

how often a form of a gene appears in a gene pool

artificial selection

selection by humans for breeding of useful traits from the natural variation among different organisms

founder effect

change in allele frequencies as a result of the migration of a small subgroup of a population forming a new population

natural selection

a natural process resulting in the evolution of organisms best adapted to the environment

genetic drift

The gradual changes in gene frequencies in a population due to random events

gene flow

exchange of genes between populations


movement of individuals (and therefore alleles) into a population


movement of individuals (and therefore alleles) out of a population

bottleneck effect

Genetic drift resulting from a drastic reduction in population size

Stabilising selection

extremes variations are selected against.

directional selection

one extreme is selected for

disruptive selection

extreme phenotypes are selected for over the intermediate forms.

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