VMBO Year 2 · HAVO/VWO Years 2–3 · Inheritance and evolution · Section 5.1
Genotype and phenotype
Inherited information
Most human body cells have a nucleus containing 46 chromosomes. Chromosomes consist of DNA and associated proteins. DNA stores information involved in inherited characteristics.
Before ordinary body-cell division, DNA is copied. The resulting daughter cells usually receive the same genetic information. Approximately half of a person's nuclear chromosomes come from each biological parent.
Genotype
A gene is a section of DNA containing information used by cells. One characteristic may depend on several genes, and one gene may affect several characteristics.
Genotype refers to an organism's genetic makeup, or to its allele combination for a particular gene being studied. Its starting combination is established at fertilisation. Most cells retain this information, although mutations can cause changes.
Most body cells contain the same genes but use different ones according to their function. Some specialised cells, such as mature red blood cells, have no nucleus.
Active genes
Only some genes are active in a given cell at a given time. Different patterns of activity help make cell types different. For example, liver cells perform tasks involved in bile production, while cells in hair follicles make hair.
Levels of gene activity
Genes can be active to different degrees, affecting how much of a product is made. Cells can adjust gene activity in response to signals and changing needs; pancreatic cells, for example, regulate insulin production and release.
Phenotype
The phenotype includes an organism's observable and measurable characteristics, not just its visible appearance. Examples include eye colour, muscle development and blood pressure.
Phenotype results from interactions between genotype and environmental influences, including lifestyle. Dyeing hair purple changes appearance without changing the inherited DNA sequence.
Some characteristics are strongly influenced by genes, while others, such as a scar, reflect environmental events. Many, such as muscularity, involve both.
Glossary
- Cell division
- A process producing new cells; ordinary body-cell division follows DNA copying and normally produces two daughter cells.
- Chromosomes
- Structures containing DNA and proteins that carry inherited information.
- DNA
- The molecule storing genetic information.
- Daughter cell
- A cell formed by division of a parent cell, usually with the same genetic information in ordinary body-cell division.
- Phenotype
- Observable and measurable characteristics resulting from genotype and environmental influences.
- Gene
- A section of DNA containing information used by cells and contributing to biological characteristics or processes.
- Genotype
- Genetic makeup, either overall or for a particular gene or set of genes.
- Body cells
- Cells forming the body, most of which contain the same set of nuclear genes.