Lavinia Buckenham Baines, of Ilam School, asks :-

Why does this world only have boys and girls?

Frank Sin, a Geneticist at the University of Canterbury, responded.

All living things such as plants, animals and people are built with millions and millions of building blocks, called cells. Like the Lego blocks, these cells can have different sizes and shapes, but they all have a set of memory banks, called chromosomes. In people there are 46 of such memory banks in each cell; cats have 38.

Why are there boys and girls? This is because in almost all plants and animals, including people and cats, two of the memory banks in each of the cells store information for boys and girls. These are called the X and Y chromosome. Girls have two Xs, while boys have one X and one Y.

Funny things do happen in some fish. For example, a father salmon can change into a mother salmon when it has grown to a certain size. In other fish, such as reef wrasses, a mother fish can change into a father fish. In some lizards there are only girl lizards, but they can behave like a boy or a girl depending on some chemical changes inside them. Even in plants such as gum trees the flowers can change from a boy to a girl flower within a few hours. All these different forms are thought to be good for the future generations.