VMBO Year 3 · Organs and cells · Section 1.4
Chromosomes
What are chromosomes?
Most human body cells contain a nucleus with long structures called chromosomes. Chromosomes consist of DNA and proteins. DNA carries information that contributes to inherited characteristics, such as eye colour and a tendency to develop freckles.
When can you see chromosomes?
Between cell divisions, chromosomes are spread out as thin strands and cannot normally be distinguished individually with a light microscope. Before and during cell division, the DNA becomes tightly coiled and the chromosomes become shorter and thicker. They can then be seen using suitable staining and a microscope.
Chromosome pairs and numbers
In most human body cells, chromosomes occur in pairs. One chromosome of each pair comes from the mother and one from the father. Corresponding chromosomes carry genes for the same types of characteristics. Most human body cells contain 46 chromosomes: 23 pairs. There are exceptions: mature red blood cells have no nucleus, and sex cells contain 23 unpaired chromosomes.
Different species, different numbers
Different species usually have a characteristic chromosome number. In organisms with two sets of chromosomes, the chromosomes generally occur in pairs, giving an even total. This is not a rule for every organism or every type of cell.
Glossary
- Chromosomes
- Structures made of DNA and proteins, carrying genetic information passed from parents to offspring.
- Chromosome pairs
- Corresponding chromosomes carrying genes for the same types of inherited characteristics, usually one from each parent.
- DNA
- The molecule carrying genetic information that can be passed from parents to offspring.
- Inherited characteristics
- Features influenced by genetic information received from parents, such as eye colour or a tendency to develop freckles.
- Body cells
- Cells forming an organism's body, as opposed to its sex cells. Most human body cells have 23 chromosome pairs.