genetic inheritance

Gamete

A male or female organism's reproductive cells such as the sperm or egg, carries half the genetic material of one parent

Chromosomes

Molecules of tightly-packed DNA that are wrapped up by proteins and contain many genes

Inheritance of chromosomes

Organisms inherit one copy of each chromosome from their mother and one copy of each chromosome from their father

Number of inherited chromosomes in humans

23 chromosomes are inherited from a mother's egg cell and 23 chromosomes are inherited from a father's sperm cell, a total of 46 chromosomes or 23 pairs

Gene

A small section of DNA that acts as a code for a specific characteristic

Alleles

Different versions or form of the same type of gene, the interaction of two alleles determines the overall displayed characteristic

Two version of each gene

There are two alleles present for each gene in an human, as humans have two copies of each chromosome

Allele representation

Individual alleles are written as single letters, if it is a dominant allele it is capitalised or if it is a recessive allele it is written in lowercase

Dominant

An allele that is always expressed, even if only one copy of the allele is present, for example "A" in AA or Aa

Recessive

An allele that is only expressed if two copies of the allele are present, for example "a" in aa

Homozygous

When the two alleles present in an organism are the same, for example AA or aa

Heterozygous

When the two alleles present in an organism are different, for example Aa

Genotype

The genetic features of an organism, specifically the combination of alleles that an organism has for a particular characteristic

Phenotype

The observable properties or characteristics of an organism that is the result of interaction between an organism's genotype and its environment

Genotype affects phenotype

The combination of alleles operate at a molecular level to develop characteristics that can be expressed as a phenotype

Single-gene expression

Some characteristics are controlled by a single gene, such as fur colour in mice and red-green colour blindness in humans

Multiple gene interaction

Most characteristics are a result of multiple genes interacting rather than a single gene

Punnett square

A diagram used to predict an offspring's possible genotypes, following the cross of a male parent with a known genotype and a female parent with a known genotype

Genetic cross

The purposeful mating of two individuals resulting in the combination of genetic material in the offspring

Probability

Punnett squares are used to work out the probability or chance that an offspring will have a specific combination of alleles

Ratio, fraction or percentages

Expressions of probability, for example a 1 in 4 chance could be expressed as 1:3, 1/4 or 25%