Know that a new individual develops when a male cell (sperm) combines
with a female cell (ovum). Soon after the sperm penetrates the ovum, the
head of the sperm divides and releases twenty-four small bodies in the
nucleus of the cell
(chromosomes). These chromosomes pair with those of the ovum which also
number twenty-four. The new individual, therefore, starts life with
forty-eight chromosomes, each different from the others in shape and
size. Through a process of division and re division, each cell in the new
individual eventually has an exact duplicate of the original set of
chromosomes. This explains why a child resembles his father's family in
some respects and his mother's family in others, for the chromosomes
carry the characteristics of the families concerned.
Each chromosomes is made up of small elements called genes which
are inherited from the parents. Each pair of genes, one from the father
and one from the mother, is responsible for a particular aspect of a
child's development. Each pair determines some physical feature of the
child.
The genes contain the hereditary factors which determine eye and hair color and quality, height, shape of the head and facial features, skin color and other physical features. There are traits which are strong or dominant and traits which are weak or recessive
When a gene carrying a dominant trait is paired with a gene carrying a recessive trait, the dominant
trait is transmitted to the child. This explains why a child, for
example, has his father's height or his mother's nose. Other paired
genes join to produce a seeming combination of both traits which
explains a skin color somewhere between that of the father's very dark
skin, and the mother's which is very fair.
Heredity also influences the nervous system and affects the child's mental development. Let us distinguish two important terms: aptitude and ability. Aptitude is a pattern of traits needed for learning a particular task. Ability
is the power to do the task. Our abilities depend to a considerable
extent upon our aptitudes. Aptitudes are inherited; abilities are
acquired through practice. If you are an excellent musician,
painter or sculptor, will your children be excellent artists, too? If
you are a bright student, will your children also be bright student?
Aptitudes for the arts or for scholarship
are inherited, but artistic or scholastic abilities must be built upon
aptitudes through proper training and experience. Aptitude alone does
not mean ability to perform the task. Aptitudes set a limit on ability,
but training and experience will help determine how far you can develop
your abilities. Abilities are developed; not inherited. Things that you
do to improve yourself mentally or physically cannot be passed on to
your offspring through heredity.
There are hereditary factors transmitted to the child by parents for traits they do not show
themselves. This explains why a child may not resemble either parent
but resembles relatives on both sides. The parents, of course, received
their physical characteristics from the chromosomes of their own parents
who in turn received theirs from the respective parents, and so on, as
far back as we can imagine. This explains why members of a family do not
always resemble each other as a result of the various combinations
of the genes. You can also understand why these members of the family
are at the same time more like each other than the people outside their
family.
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