If we believe that chromosomes contain genes (see post 21.10), then genes must be made of either DNA or a type of protein called a histone – because that’s what chromosomes are made of. The question is then – are genes made of DNA or histones? In the early 1940s, most people believed that genes… Continue reading 21.11 Genes are made of DNA

Before you read this, I suggest you read post 21.9. In post 21.9, we saw how cells can divide to produce copies of themselves during growth or to replace old cells in a process called mitosis. During mitosis, chromosomes appeared in the cell nucleus. These chromosomes appeared in pairs, so we can say that each… Continue reading 21.10 Chromosomes 2 – meiosis

A biological cell is transparent and so is difficult to see with a microscope. Biologists usually dye cells before they use a microscope to examine them. The dyes they use are called stains and the dyeing process is called staining. A stained animal cell then shows the features in the picture above – it is… Continue reading 21.9 Chromosomes 1 – mitosis

People have been selectively breeding animals and plants for thousands of years – to provide better sources of materials for food and clothing or for decoration. Carassus auratus is a small brown fish related to the carp. But, occasionally, an individual appears with an unusual shape or colour (usually red or yellow). By selectively breeding… Continue reading 21.8 Genes