What Are Chromosomes? GCSE Biology Explained
Learn what chromosomes are, where they are found, how they carry genes, and why they are copied before cell division for AQA GCSE Biology exams in clear notes.
Chromosomes are structures made of DNA that carry genetic information. In animal and plant cells, they are found inside the nucleus. Each chromosome carries many genes.
Chromosomes, DNA and genes
These terms are closely connected but do not mean the same thing:
- DNA is the chemical that makes up genetic material.
- A chromosome is a structure made of DNA.
- A gene is a small section of DNA found on a chromosome.
Genes contain the instructions that help determine an organism’s characteristics. They also control the production of particular proteins.
In human body cells, chromosomes are normally arranged in 232323 pairs. One chromosome in each pair is inherited from each parent.
What happens during cell division?
Before a cell divides, it grows and increases the number of sub-cellular structures, such as mitochondria and ribosomes. Its DNA then replicates, meaning that it is copied. This produces two copies of each chromosome.
During mitosis, one set of chromosomes is pulled to each end of the cell. The nucleus divides, followed by the cytoplasm and cell membrane. This produces two genetically identical cells.
Worked example
Suppose a skin cell needs to divide for growth or repair:
- The cell grows.
- Its DNA replicates, copying each chromosome.
- One set of chromosomes moves to each end.
- The nucleus and then the rest of the cell divide.
- Two identical cells are produced, each containing the same genetic information.
Common exam mistake
Do not say that chromosomes are “made of genes”. Chromosomes are made of DNA, while genes are sections of that DNA.
This answer assumes AQA GCSE Biology 8461 Higher tier and the separate Biology qualification. However, the chromosome content explained here is common to both Foundation and Higher tiers and is not biology-only content.
