Threads of information

The idea

Chromosomes are thread-like structures in the cell nucleus that carry genetic information; each species has a fixed number, humans having 23 pairs (46), each pair with one chromosome from each of two individuals.

Same number every time

The cells of a human have a fixed number of tiny thread-like structures inside the nucleus. Another species has its own fixed number.

What do you think these threads carry?

• Information about the characters of the living being
• The food for the cell
• Oxygen for breathing

Into the nucleus

Press Next step to look closer and closer.

Fixed number, in pairs

The threads in the nucleus are chromosomes. Each species has a fixed number of them, and they form pairs.

Chromosomes are thread-like structures in the cell nucleus that carry genetic information. Each species has a fixed number. Humans have 23 pairs (46), each pair with one chromosome from each of two individuals.

Notes

Chromosomes in the nucleus carry genetic information. Each species has a fixed number; humans have 23 pairs (46).

Check yourself

Humans have 23 pairs of chromosomes. How many chromosomes is that in all?

Answer: 46

23 pairs × 2 = 46 chromosomes.

A human cell has 46 chromosomes. How many pairs are there?

Answer: 23

46 ÷ 2 = 23 pairs.

Where in a cell are chromosomes found?

In a pair of chromosomes, the two chromosomes come…

• In the nucleus — correct. Yes!
• Outside the cell. Chromosomes are in the nucleus of a cell.
• Only in the food stored by the cell. Chromosomes are thread-like structures present in the nucleus.
• both from the same individual. Each pair has one chromosome each from two different individuals.
• one from each of two individuals — correct. Yes!
• from the nucleus of a different species. Each species has its own fixed number. The two in a pair come from two individuals.