Biology - inheritance

Genome

The entire DNA of an organism

Gene

A section of a molecule of DNA that codes for a combination of amino acids to make a specific protein

Homologous chromosomes / autosomes

Chromosomes that have the same genes, in the same location. There are 22 homologous pairs of chromosomes in human nuclei.

Alleles

Different forms of the same gene

Dominant

An allele that is always expressed in the phenotype when present in the genotype (regardless of the other allele)

Recessive

An allele that is seen in the phenotype only if two copies are present in the genotype and there is no dominant allele present

Homozygous

This describes a genotype in which the two alleles for a particular characteristic are the same

Heterozygous

This describes a genotype in which the two alleles for a particular characteristic are different

Phenotype

The visible characteristics of an organism which occur as a result of its genetics and the environment

Genotype

The DNA an organism has for a certain characteristic

Monohybrid inheritance

Inheritance of one gene

Sex chromosomes

The 23rd pair of chromosomes in humans (not homologous), XX in biological females and XY in biological males

Chromosome

A structure made of a long length of coiled up DNA

Codominance

When two alleles are both expressed in the same phenotype (e.g. blood group AB)

Selection pressure

An environmental factor that affects the chance of survival of an organism

Mutation

A rare, random change to the sequence of bases in DNA

Uses of mitosis

Growth, repair, cloning, asexual reproduction

Use of meiosis

To produce gametes, for sexual reproduction

Continuous variation

A characteristic that changes gradually over a range of values shows continuous variation. Examples include height, weight and handspan.

Discontinuous variation

A characteristic with a limited number of possible values shows discontinuous variation. Examples include eye colour, blood group and biological sex.