What will your baby inherit? What will he be like? Will he be fat or thin ? Will he be tall or short ? Fair or dark ? Will he have blue eyes like you or the athletic prowess of his father? As they sit and think and let their minds wander over the whole range of combinations that may affect, and therefore alter, the appearance and character of an unborn baby, there is usually a time when both the mother and father become more serious and perhaps a trifle anxious. Will he be normal ? Will he be perfect ? All mothers and certainly f most fathers experience this apprehension at some time during a pregnancy and for the majority it remains a lurking anxiety that is only satisfied after the safe delivery of a healthy, normal baby.
Despite the fact that 97 per cent of babies are perfectly normal, anxiety over the normality of your own child is understandable. Some people, however, cannot stop worrying about the health of their unborn child, usually because there is some disease or disorder somewhere in the family. A relative may have suffered from a nervous breakdown; a grandfather may have been a diabetic, or someone may suffer from, tuberculosis or someone else from cancer. Even such minor abnormalities as colour blindness, bat ears or a crooked toe can occasionally cause immense worry and distress to a woman throughout her entire pregnancy.
A great deal of information is now available on hereditary factors, or genetics, and genetic counselling is’ becoming a rapidly expanding part of the medical services available to anyone who wishes to enquire into the chances of any trait, good or bad, being handed down to their baby.
Very few, if any, of us ever pause to think why we are who we are, and why we have developed into our present unique, physical and mental personalities. Few people appreciate that an average number of 400 million spermatozoa (sperms) may be deposited with each ejaculation and that any one of these 400 million sperms is capable of fertilizing an ovum. The first and perhaps the greatest battle for survival is fought amongst these 400 million sperms only one of whom may succeed in fertilizing the ovum. It seems reasonable to suppose that this is one of nature’s ways of eliminating both the weak and the unhealthy, for only the strongest sperms can survive the journey through the cervix, up the uterus and along the Fallopian tube to arrive in a sufficiently fit and .healthy state to have the power to fertilize by penetrating the outer cell membrane of the ovum.
Each sperm, as well as every ovum, contains 23 tiny rod-shaped chromosomes, every one being formed in a chain-like structure by thousands of smaller beads known as genes. Every single detail of a person’s anatomy and personality is dependent upon a specific factor present in the genes so that, at the moment of conception when the 23 chromosomes of the sperm join with the 23 chromosomes of the ovum to form the 46 chromosomes which are normally present in a human cell, a complete ‘ working drawing’ of the subsequent human is laid down to the ultimate detail. Environment and environmental changes in the uterus, as a baby, a child, an adolescent and later throughout adult life, may change certain aspects of anatomy, physiology or personality, but nevertheless the precise form of the future person is decided exactly by the genes carried within the chromosomes of both the sperm and the ovum. Half the chromosomes, including therefore half the genes, have come from the mother and half have been produced by the father. Thus a person may inherit or develop characteristics from either parent. It is this choice of inheritance from two people which gives a certain amount of latitude and variation to nature, allowing hereditary trends to develop within a species’which may gradually change certain aspects of that species.
All human beings develop from one ovum and one sperm each containing half the adult number of chromosomes, so that when fertilization occurs they weld together to form a single cell containing the correct number of chromosomes required to be present in each cell of the adult body. The fortune of one’s biological inheritance is even greater when one considers the process of natural selection which has also been taking place in the ovary prior to the production of a single ovum. At the time of birth the ovaries in a female baby already contain all die ova that she will produce during her adult life. The ovaries do in fact contain many more than she will require, since they each contain approximately 40,000 ova. The average woman starts to ovulate (produce ova or eggs) at about the age of 13 and thereafter ovulates once with each menstrual cycle until the age of approximately 45. Some menstrual cycles may not be associated with an ovulation, whilst others are suppressed by either pregnancy or lactation. Most women will Ovulate for about 25 years, so the number of Ovulating cycles will be 13 per year for 25 years—that is 325 ova, or eggs, will be produced throughout the life of the average woman. At the beginning of each menstrual cycle somewhere between 100 and 150 ova will start to ripen in each ovary but only one will be successful. Each ovum will have a slightly different gene pattern, although the number of chromosomes will be the same.
The arrangement of the genes within the chromosomes is known as the genetic pattern. Each ovum, when it starts to mature at the beginning of the menstrual cycle, will have a slightly different genetic pattern, so that when the possible variations of genetic pattern amongst the ova and the sperms are considered it is easy to realize how variations in the final form of the eventual individual may arise. Each ovum has a chance of about 1 in 250 of being selected and each sperm, 1 in 400 million, so that the overall chance of obtaining a particular genetic pattern is in the region of 1 in 100,000 million.