biology science - genetics - definitions

Variation

The differences in characteristics of a population.

Continuous variation

describes characteristics that can change over a range of values. Examples can be affected by environmental and inherited factors. eg. height.

Discontinuous variation

describes characteristics that can be one of a limited number of options. Can only be affected by inherited factors. An example is eye colour.

Characteristic

A distinctive, specific trait of an organism.

inherited characteristics

When you gain characteristics from your parents through genetics eg. brown eyes.

Environmental characteristics

When you gain characteristics from external factors eg. a scar.

DNA

The molecule that contains the genetic information of an organism. (deoxyribonucleic acid)

Gene

A small segment of DNA

Dominant allele

When only one allele is required to be present in an organism's genotype for the characteristic to be expressed.

Recessive allele

When two alleles are required to be present in an organism's genotype for the characteristic to be expressed.

Nucleotide

The building block of DNA, made up of a nitrogenous base, a phosphate group and a sugar.

Nitrogenous base

A molecule that contains nitrogen and has the chemical properties of a base. Adenine (A), thymine (T), cytosine (C), and guanine (G). A+T, G+C.

Allele

A variation of a gene (eg gene is eye colour, this is blue eyes).

Phenotype

The expressed, observable alleles of an organism for a particular gene.

Genotype

All alleles present within an organism for a particular trait.

Punnett square

A method used in order to predict the phenotypes and genotypes of the offspring of a cross between organisms.

Homozygous

When an organism's genotype contains two of the same alleles (could be dominant or recessive).

Heterozygous

When a person's genotype contains two different alleles.

Chromosome

A tightly wound package of DNA found inside the nucleus of the cell.

Pedigree chart

A method of viewing information about a family's genetic traits.

Karyotype

All of the chromosomes within an organism, arranged in an organised way.