Chromosomes

A chromosome is a long DNA molecule associated with proteins. It carries many genes, which are sections of DNA. A gene can exist in different versions, called alleles.

In body cells, chromosomes generally occur in pairs. One chromosome of each pair is inherited from each parent. The two chromosomes in a pair carry the same genes at corresponding positions, but they do not necessarily carry the same alleles. For example, they may carry different alleles of the same gene.

Gametes, such as egg and sperm cells, normally contain one chromosome from each pair. When an egg and sperm join, the new cell receives one chromosome of each pair from each parent.

Cell nucleus

The nucleus is a membrane-bound structure in eukaryotic cells. It contains chromosomes, which carry the cell’s genetic information.

The membrane surrounding the nucleus is called the nuclear envelope. It separates the genetic material inside the nucleus from the cytoplasm outside it.

Chromosomes contain genes. Genes hold information used to make proteins, and proteins help control the cell’s activities. In this way, the genetic information in the nucleus helps direct what the cell does.