We have known for a long time that characteristics are passed from parents to their children. But science has only recently discovered exactly how this information passes between generations.
In 1953, James Watson and Francis Crick showed that DNA is shaped like a spiral staircase, commonly known as the double helix. This is an efficient way of storing the huge quantity of genetic information in each cell and it also helps cells to divide correctly. In 1962, Watson and Crick, along with Maurice Wilkins, won a Nobel Prize for their discovery.
Fig. 4.1.4 Watson and Crick
Chromosome Numbers The DNA race
The race to understand DNA was long and eventful.
Research the controversy surrounding the race to understand DNA and prepare a short multimedia presentation for your classmates.
Every human body cell contains 46 chromosomes, except gametes. Gametes are the cells involved in reproduction. z The male gamete is a sperm. It contains 23 chromosomes. z The female gamete is an egg. It contains 23 chromosomes.
During human reproduction the male sperm and the female egg fuse and a single cell called a zygote is produced. This is called fertilisation. We will learn more about how fertilisation takes place later.
The zygote contains 46 chromosomes. Twenty-three of these chromosomes come from the father and the other 23 come from the mother.
The new zygote has a unique combination of genes inherited from both the male and female parent and shares certain characteristics with both.
