What is Down’s syndrome?
Down’s syndrome is a condition caused by the appearance of an extra chromosome in the embryo. This extra chromosome is repeated in all the body cells. A child with Down’s syndrome has 47 chromosomes instead of the usual 46, and this difference causes physical and mental changes.
How do I inherit genes from my parents?
Sperms and egg cells contain only half of the normal number of chromosomes. During fertilization these chromosomes combine to make up the usual total of 46 chromosomes. This means that half of a baby’s genetic information comes from the mother, and half from the father, mixing together their characteristics in a random order. In this way you develop a mixture of characteristics from both parents.
Are there such things as ‘bad’ genes?
Some genes cause us to inherit a harmful condition. The disease haemophilia is an example of such a ‘bad’ gene. It is handed down through the male side of the family but the disease is carried on the female, or X, chromosome. This means that women pass the disease on to their sons, even though they are not affected themselves. Haemophilia will not affect a female unless both parents have the gene, which is a very rare occurrence.
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