Chromosomes

• Chromosomes are thread-like structures located inside the nucleus of animal and plant cells.
• Each chromosome is made up of protein and a single molecule of deoxyribonucleic acid (DNA).
• DNA contains all the specific instructions that make each type of living creature unique.
• The DNA molecule in a chromosome is so long, it must be ‘coiled’ up to fit inside the cell.
• Humans normally have 23 pairs of chromosomes in each cell, totalling 46. The only cells that do not contain a full set of chromosomes are the sex cells, or gametes which have half the number.
• Chromosomes are best seen in the nucleus during cell division, whether mitosis or meiosis.
• Chromosomes are responsible for determining the inherited characteristics of every organism.
• The 23rd pair of chromosomes, known as the sex chromosomes, differs between males and females. Females have two copies of the X chromosome, while males have one X and one Y chromosome.
• During cell division, it is vital that each new cell receives the correct number of chromosomes. Errors can lead genetic disorders. For example, Down’s syndrome is caused by having an extra copy of chromosome 21.
• Understanding chromosomes helps us to study and comprehend genetic diseases, human biology, and evolution.
• Chromosome structure, numbers, and types are some of the key points used in the study of genetics.

In cell division and stem cell topics, attention should be given to the role of chromosomes in mitosis and meiosis, and the potential for errors during these processes.