The baby’s sex is determined at the moment of. The genes of the egg have no part in deciding this — it’s up to the sperm. Sperm, are divided roughly equally into those carrying ‘male making’ genes and those carrying ‘female making5 genes. Whether it’s a boy or girl depends on which type penetrates the egg.
There is little a couple can do to alter the mathematical chances involved: 50.5 per cent chance of a boy being produced atand a 49.5 per cent chance of it being a girl. Ideas about a certain position for intercourse producing one sex or the other are mosdy based on folklore, going back to the ancient Greek myth that boy children were lodged on the right-hand side of the and the girls on the left – which is simply not true.
Research work is being done on how the acidity of the vagina may affect the odds; it is believed that male-making sperm are more active in a slighdy acid vagina while female-making sperm are more active in a slightly after a few days abstinence. For a man with a alkaline environment.
Normal sperm count this actually makes no great In die past some people used to be recom- difference. With a low sperm count, this ‘saving mended a douche using vinegar or sodium up’ of sperm for two or three days helps a bit, but bicarbonate. These were a terrible nuisance and longer than that makes no difference. Used to put many people off intercourse corn- Some women produce a particularly thick pletely. Newer techniques include the use of gels mucus from the neck of thewhich sperm – which are more elegant than douches and are find difficult to penetrate. Medical treatment formulated to alter slightly the acidity of the may help thin this to make fertilization easier. Vagina. Research into this is still in progress.
There are two sorts of twins – identical and nonidentical. Identical twins are made from one egg fertilized by one sperm. When the fertilized egg divides to form two cells, normally these stick together, and go on to reproduce, making 4, 8, 16, 32 cells and so on. In some rare cases, however, at the two cell stage the clump divides completely and instead of going on to form a four cell unit, makes or two cell So two absolutely identical clumps of cells are made. Each of these goes on to develop into a separate individual with a common genetic background – the result is identical twins.
Nonidentical twins are the result of a woman making more than one egg during the menstrual cycle. If the two eggs are fertilized by two separate sperms they will develop into two separate individuals with genetic backgrounds. They may also be of different sex, and bear no more resemblance to each other than any other brother or sister – they simply share the sameat the same time. Identical twins, however, not only look like each other, they often resemble each other mentally and psychologically – even if they are separated and brought up in different families.