VMBO Year 3 · Inheritance and evolution · Section 3.1

Genotype and phenotype

What are genotype and phenotype?

Most human body cells have 46 chromosomes, made of DNA and proteins. Their DNA carries inherited information. An organism's genetic information is its genotype. This is largely maintained throughout life, although DNA changes called mutations can occur. Its observable or measurable characteristics form its phenotype. These include appearance, such as eye colour and hair structure, but also characteristics such as blood pressure and aspects of behaviour.

How is genetic information inherited?

At fertilisation, chromosomes from the father's sperm and the mother's egg come together. Each sex cell contributes one chromosome from each pair, restoring the paired sets. For most genes, a person therefore inherits two alleles: one from each parent. There are exceptions, including genes on the sex chromosomes.

Genes and alleles

A gene is a section of DNA carrying information for a functional product and contributing to characteristics. Each chromosome contains many genes. An allele is a version of a gene. The two copies a person carries may be the same or different. A gene does not itself consist of two alleles: the alleles occupy corresponding positions on the two chromosomes. Many characteristics, including human hair colour, are influenced by several genes.

Environmental influences

Phenotype is influenced by genotype and environment. Sunlight, diet and stress can affect characteristics. Dyeing hair changes its appearance without changing its inherited DNA. Newly growing hair retains its genetically influenced colour. Environmental effects are not always temporary, but a change in appearance does not automatically change the genotype.