chromosome

Everyday

1. A chromosome is a tiny thread-like structure inside the centre (nucleus) of a living cell, made of DNA, which carries the instructions (genes) for how a living thing grows and works. tree →
2. Humans usually have 46 chromosomes in each cell, in 23 pairs: one of each pair comes from the mother and one from the father. tree →

In the lessons

In science lessons on inheritance and genetics, chromosomes explain why children look like their parents. The X and Y chromosomes are involved in whether a baby is usually born a boy or a girl. Some people are born with an extra chromosome, as in Down syndrome; they are just as valued as anyone. Phrases: «X chromosome», «Y chromosome», «pairs of chromosomes».

Examples

• Chromosomes are inside the nucleus of a cell. tree →
• People usually have 23 pairs of chromosomes. tree →
• Each chromosome carries many genes. tree →
• You get half your chromosomes from each parent. tree →
• People with Down syndrome have an extra copy of chromosome 21. tree →
• We looked at a picture of chromosomes under a microscope. tree →

Note

Countable. Pronounced KROH-muh-sohm. In number problems: 23 pairs = 46 chromosomes (23 × 2); an egg or sperm cell has only half, 23. Chromosomes, genes and DNA are linked: DNA makes up genes, and genes sit on chromosomes.