The full set
Half of your DNA comes from your mum and half from your dad. When the sperm and egg combined to make you, 23 chromosomes from the egg combined with 23 chromosomes from the sperm to form a full complement of human DNA - 46 chromosomes.
Chromosomes pair up and copy themselves every time before cells divide. This division happens billions of times in your lifetime as you grow, and to replace old cells (like skin cells or cells in the lining of your mouth).
If a cell is stopped during cell division, and stained with Giemsa dye, the 23 pairs of human chromosomes are visible with a light microscope. The dye stains regions of chromosomes that are rich in the base pairs adenine (A) and thymine (T), producing banding patterns in the chromosomes, each one different from the rest.
Genetics Education, Murdoch Children's Medical Research Institute
DNA is packaged so tightly together that even the thinnest bands contain over a million base pairs and potentially hundreds of genes.
The chromosomes can be matched in their pairs, arranged and numbered by size from largest to smallest based on the banding patterns that you see and the position of the centromere. The centromere is the central most condensed and constricted region of a chromosome and also the part to which the spindle fibre attaches during cell division to allow the chromosomes to separate.
Genetics Education, Murdoch Children's Medical Research Institute
Once the chromosomes are lined up, this is called a karyotype.
If a person has too many or too few chromosomes, missing pieces of chromosomes, or mixed up pieces of chromosomes, it can lead to a genetic disease. Karyotyping is one of many techniques that can detect chromosomal abnormalities, by looking at the number and structure of chromosomes.
Cytogenetics is the study of chromosomes using a microscope.
Chromosome preparations can be taken from different types of tissue including blood, bone marrow, amniotic fluid, and embryos.
Go on a chromosome hunt and put together a karyotype - www.genecrc.org/site/ko/ko5c.htm