A baby develops from the union between the mother's egg and the father's sperm. This union determines what the child will be like, such as how tall he or she will be, what colour the eyes will be, and what the shape of the nose and mouth will be. How the parents pass these characteristics to their child is called genetics.
Each cell in the human body contains 46 structures called chromosomes. The reproductive cells, that is, the male sperm and the female egg, each contain only 23 chromosomes - half as many as all other cells in the human body. Each chromosome is made up of many genes, and it is these genes, half of which come from the father and half from the mother, that combine to determine what a person will be like.
Some families would rather have sons than daughters, and in parts of Africa women are blamed if they do not bear sons. Some wives have been divorced for not producing a son. In actual fact, however, it is the father, not the mother, who determines whether the baby is a boy or a girl.
How? A sperm contains 22 regular chromosomes and one sex chromosome, either X (female) or Y (male). All eggs contain 22 regular chromosomes and one sex chromosome, which is always X (female). If a sperm with a Y chromosome fertilises the egg, the baby will be a boy, and if a sperm with an X chromosome fertilises the egg, the baby will be a girl (see Figure 5.1).
Children inherit other characteristics from their parents besides height and the colour of their eyes. Certain physical or mental disorders can also be passed from one generation to the next. Among Africans, or people of African descent, two well-known conditions that can be passed from parents to their children are sickle cell disease and albinism.
Figure 5.1: How the Sex of the Baby is Determined
SICKLE CELL DISEASE
Sickle cell disease affects the blood cells and, in particular, the ability of the blood to carry oxygen to the tissues of the body. The disorder is quite common in Africa. In its severe forms, it causes a great deal of illness, pain, and even early death. It can also cause serious complications during pregnancy.
The abnormality which causes sickle cell disease is contained in the genes a person inherits from his or her parents. If both parents suffer from the disease -that is, they each have a pair of sickle cell genes - all their children will have the disease. On the other hand, if both parents are carriers - that is, they each have one sickle cell gene - each child has a 25% chance of being completely normal, a 50% chance of being a carrier, and a 25% chance of having the severe form of the disease. It is possible for a couple to produce a number of children with sickle cell disease even if both parents are only carriers; it is equally possible for such a couple to produce a number of children who do not have the disease. If one parent is normal and the other parent is a carrier, each child has a 50% chance of being born completely normal, and a 50% chance of being a carrier.
All couples, therefore, should have a blood test to determine whether they have the sickle cell disorder before they try to have a baby. Couples who are likely to have a baby with sickle cell disease should be informed about their chances, so that they can decide whether to run the risk or, perhaps, adopt a baby instead.
Albinos lack skin pigmentation - that is, their skin is white instead of dark, their hair is light yellow instead of black, and their eyes are blue instead of brown or black. Albinism is another condition common in Africa that children inherit from their parents. It cannot be caught or "transmitted" from person to person; it can only be passed from parent to child. Both parents of an albino must either be albinos or carriers. Because albinos lack skin pigmentation which protects people from the sun, they are more likely to get skin cancer from being in the sun too much. Albinos should always cover their skin as much as possible and avoid being in the sun.
On average, about one out of every 85 pregnancies results in the birth of twins. Triplets, quadruplets, and higher numbers are less common. A woman who is a twin herself, or who has a close relative such as a mother or sister who is a twin, has a higher chance of having twins. Older women and women who are very fertile (more likely to release two eggs at once) are also more likely to have twins.
There are two types of twins, identical and fraternal. About one-fourth of all twins are identical. This means they develop from the same fertilised egg which, for reasons not properly understood, divides into two separate groups of cells, each of which then develops into a separate individual. But because they develop from a single fertilised egg, identical twins have exactly the same genes. They are always the same sex, and not surprisingly, look almost exactly alike.
Fraternal twins develop when, at ovulation, a woman's ovaries release two eggs instead of just one. Both eggs are then fertilised by different sperm, and grow in the womb at the same time. Apart from growing inside the same womb at the same time, fraternal twins have no more in common than any two children of the same parents. They may be of different sex.
When a mother hears her newborn baby cry for the first time, many thoughts and feelings may come to her: Is it a boy or girl? Is it healthy? Does it have any deformities?
Unfortunately, a small percentage of babies are born with some form of abnormality. These can be minor, such as a cleft palate (a problem with the upper lip and top of the mouth), or more serious, such as mental retardation or heart problems. Considering the millions of changes that take place between fertilisation and birth, it is a miracle that the overwhelming majority of children are born healthy and normal. As discussed in Chapter 9, most foetuses that have severe abnormalities miscarry by themselves. Some abnormalities, such as a cleft palate, can be corrected by an operation, especially if it is done while the child is still very young. Others cannot, so the child and his or her family must learn how to manage, and try to help that child develop as fully as possible. While this can be difficult, it can also help make a family closer and more caring.
WHAT CAUSES ABNORMALITIES IN A BABY?
In the past, and still in some countries today, a deformity in the baby was thought to be the result of witchcraft, adultery, sin, or a curse. Today, the causes of some abnormalities are still not known, although many are. For example. Down's Syndrome (mental retardation) is due to problems in the baby's genes that can come from either the father's sperm or the mother's egg. Other abnormalities can be caused by illness during pregnancy, such as German measles or syphilis. Some medicines, if taken during pregnancy, can also cause abnormalities. For example, tetracycline (an antibiotic) can cause damage to the baby's teeth and bones. It is also considered unsafe for a pregnant woman to be exposed to too many X-rays, especially during early pregnancy. Some common chemicals used for farming or in factories can find their way into water, food, or air; if the concentrations are high enough, these chemicals can cause birth defects.
It is almost impossible to identify exactly what causes an abnormality in a baby. In most cases, only common-sense precautions can be taken, such as getting tested (and, if necessary, treated) for syphilis. Mothers should also avoid alcohol, drugs, X-rays, and harsh chemicals during pregnancy. Proper nutrition can help ensure that the baby is as healthy as possible. When all precautions are taken, the chances are overwhelmingly in favour of the child being completely healthy and normal.
Summary: What Will the Baby Be Like?
The way a child looks, as well as other characteristics, is passed on from the parents. These characteristics include:
BOY OR GIRL:
It is sperm from the father, not the mother's egg, that determines the sex of the baby.
Identical twins look alike because they come from the same egg in the mother's womb. Fraternal twins do not necessarily look alike, because they come from two different eggs even though they grow in the womb at the same time.
Some disorders or conditions, such as albinism and sickle cell disease, are passed on from the parents to the children. Others can be caused by drugs the mother takes or illnesses she has during pregnancy. Many of these can be avoided if the mother takes proper precautions during pregnancy.