Sexual and asexual reproduction

• A human baby is born nine months after its mother's egg cell (female gamete) has been fertilised by a sperm (male gamete) from the father.
  This is called sexual reproduction.
• After fertilisation, the fertilised egg is called a zygote. The zygote divides into two cells, then four cells, then eight and so on. Soon the cells begin to specialise to make organs and limbs. When this happens, the zygote becomes an embryo. The embryo will grow and become a baby girl or a baby boy. The baby (offspring) will have some similarities to both parents.
• Most plants and a few simple animals are able to reproduce asexually.
  Asexual reproduction allows cells to separate from a parent organism and then grow and develop on their own. Unlike sexual reproduction, asexual reproduction does not involve mating or fertilisation and it
  requires only one parent. For example, when one daffodil bulb is planted, it makes tiny side bulbs which grow and produce flowers after 3 or 4 years. These new daffodils are exactly like the first daffodil. The
  offspring from asexual reproduction are identical to their parent and are called clones.

The nucleus, chromosomes, genes and DNA

• The nucleus of every cell in your body contains long, threadlike structures called chromosomes.
• Chromosomes are made of long molecules of the polymer DNA (deoxyribonucleic acid).
• Sections of the DNA polymer in each chromosome make up a gene. Each gene controls the synthesis of a particular enzyme. Enzymes are the catalysts for biological processes.