GENETIC DANGERS

To understand fully why genetic dangers exist we need to take a brief glimpse into the principles or the “mechanics” of heredity. This takes us into the microscopic field of chromosomes and genes.

The word “chromosome” comes from the Greek, meaning “color-body.” This name is used because these threadlike particles located in the nucleus of each cell of the human (or other living) body are visible when a certain dye is applied. There are forty-six chromosomes in every human body cell, but only half this number, namely, twenty-three, are in the individual’s sex or reproductive cells. Therefore, when conception takes place, the fertilized egg cell has received half of its chromosomes from the father and half from the mother, to make up its total of forty-six chromosomes. This cell is the beginning of the new individual.

Lying along the threadlike chromosomes, there are untold numbers of “genes.” These are certain chemicals that operate to direct or “trigger” chemical reactions that build a certain feature of the body. At the time of conception, the chromosomes from the father carrying genes for building specific bodily features lie parallel to the chromosomes from the mother carrying similar genes. The genes for eye color, for example, will lie next to each other on the two chromosomes. The gene received from the father will cooperate or function with the like gene received from the mother. In this way the eye color of the baby is determined.

In some cases, a gene for determining some factor is “dominant” over (or “swamps” the effect of) its corresponding gene. Some genes are “recessive,” tending to be submerged in the presence of the dominant one. Because of this, a trait in the father may not appear in the child (or, conversely, a trait of the mother may be suppressed). The child will then exhibit the dominant trait​—it will be apparent in his appearance or characteristics. Nevertheless, the child’s body cells and some of his reproductive cells will contain the “recessive” gene or trait-producing unit. He will be a “carrier” of this trait, without his manifesting it himself. When he grows up and marries, if he marries a girl who has or “carries” the same “recessive” trait, then, when conception takes place, their child’s cell may receive the “recessive” gene from each parent. Their child, the grandchild of the first-mentioned individual, will then exhibit that trait that was not manifest in the personality or body of the father and perhaps not of the mother. Sometimes a “recessive” trait will be hidden for generations and then will suddenly manifest itself.

Not all “recessive” traits are bad, just as not all “dominant” traits are good. However, undesirable traits are often “recessive.” On this matter of gene combination hangs a primary reason why marriage to a close fleshly relative is very inadvisable.

An example of an undesirable “recessive” trait is albinism. This is a condition in which there is a lack of pigmentation in the skin, hair and eyes. Such persons cannot stand strong sunlight. Some ancestor in a family line may have been an albino. This characteristic will not manifest itself until two “recessive” genes for this trait, the one from the father and the one from the mother, come together. Individuals descending from this albino ancestor have a probability of being “carriers” of this gene or trait but not necessarily displaying the trait in their own appearance. Since this gene is rare, as long as a person marries someone outside his fleshly relationships the probability is strong that his marriage partner will not carry this gene, and that the children will be normal. The “recessive” gene will likely be suppressed in its action by a normal gene from the marriage partner.

On the other hand, an incestuous marriage, a marriage with a close fleshly relative, who is more likely to carry the “recessive” gene, would greatly increase the probability of albinism in the child. The closer the relative, the greater the probability. Suppose a father is an albino. Then, incestuous sex relations with his daughter will make the probability one out of two, a 50-percent chance that​—if conception results—​the child produced will be an albino. If a brother and sister, the children of this father, marry (even though neither is an albino), the probability of albinism in their child is cut to one out of four.

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UNDESIRABLE CHARACTERISTICS THAT MAY RESULT FROM A PAIR OF RECESSIVE GENES

Trait Conspicuous Signs

Acheiropody Lack of hands and feet

Albinism Lack of pigment in skin, hair, eyes

Deafness Deafness from birth

Microcephaly Abnormally small head

Phenylketonuria Enzyme disorder leading to mental retardation

NOTE: Not all these abnormalities are due to incestuous marriages. They can and do occur in other marriages, but more frequently in cases of incest.