3.1.1 Genes, Deoxyribonucleic Acids (DNA) and Chromosomes


3.1 Cell Division

3.1.1 Genes, Deoxyribonucleic Acids (DNA) and Chromosomes
1. The nucleus of a cell contains many small thread-like structures called chromosomes.

2. Chromosomes always exist in pairs (except in gametes).

3. Each chromosome contains a molecule of a deoxyribonucleic acid (DNA).

4. On each chromosome, there are genes which are the basic hereditary units.

5. A gene is a small segment of the DNA molecule. It passes genetic information from one generation to another.

6. Genes exist in pairs. One gene is inherited from the father and one from the mother.

7. Examples of genes:
  v A gene for body height
  v A gene for hair colour
  v A gene for fingerprint

8. Each organism has a specific number of chromosomes in its cell as shown in the table below.

Organism
Chromosomes number
Housefly
12
Onion
16
Frog
26
Apple
34
Human
46
Potato
48
Cow
60