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HEREDITY AND ENVIRONMENT
From the moment of conception onward, heredity and environment affect
every stage and aspect of development.
Heredity:
Every species must have a mechanism for transmitting characteristics
from one generation to the next. Heredity is that unique sum of the inherent
qualities – physical and mental – transmitted to an individual by his/her
parents at the moment he/she is conceived. After that significant moment,
there is no other possibility of him/her acquiring any other innate
characteristics. Because of that human genetic code that we inherit from
our parents, a fertilized human egg cannot grow into an elephant, eagle, or
earthworm.
Mechanisms of Heredity:
The mechanism by which heredity is passed on to a person begins
with conception, when the ovum of the mother unites with the sperm of the
father to form a zygote. The ovum and sperm merge into a cello consisting of
a nucleus surrounded by cytoplasm, the whole being enclosed in an external
membrane. The nucleus contains the genetic material that transmits
heredity characteristics from the parent to the mew individual.
What are genes?
The heredity factor hidden within the chromosomes are called genes,
which means determiners. Basically genes work in pairs, each member
coming from one of the parents, some of the genes are dominant while some
are recessive. For example, a child receives 2 genes for eye color, one from
each parent. A gene determining brown eye is dominant while one
determining blue eyes is recessive. If the child draws 2 determiners (i.e.
genes) for brown, his/her eyes will be brown. If he/she draws 1 brown gene
and 1 blue gene, his/her eyes are just as brown. To have blue eyes, the child
has to draw 2 recessive blue genes. There is no way of predicting however,
which genes are drawn from each parent and which come together in the
offspring. It is very much a chance.
Environment:
Environment is everything, other than heredity, that influences an
individual’s growth and development. Environment refers not only to the
physical surroundings but, even to thoughts and attitudes of others which
exerts an influence on the individual.
Nature (heredity) versus Nurture (environment) prompts so many questions.
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Which is more important – Nature or Nurture?
Is what we inherit the major factor in deciding what we become?
Is opportunity the reason why some succeed and others fail?
If we say, an individual is a product of, heredity and environment,
then, what proportion of a trait such as intelligence is determined by
heredity and what by environment?
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How much difference, can variation in the environment make in traits
that are partly determined by heredity?
Do some in-depth study on heredity and environment and discuss the above
issues.
STAGES OF PRE-NATAL DEVELOPMENT
Pre-natal development proceeds according to genetic instructions, from a
single cell to an extremely complex being. This development before birth,
called gestation, takes place in three stages – germinal, embryonic, and fetal.
Period
2 Weeks
3 Weeks
4 Weeks
5-8
Weeks
9-12
Weeks
13-16
Weeks
17-20
Weeks
21-24
Weeks
25-28
Weeks
29-36/38
Weeks
Description
The Germinal Period
Creation of the zygote, the cell wall division, and the attachment
of the zygote to the uterine wall. Inner and outer layers of the
organism are formed.
The Embryonic Period
Head and blood vessel from brain begins to develop.
Heart begins to beat and pump blood. Arm buds and leg buds
begin to appear and eyes, ears, nose, and mouth form. Nerves
begin to develop. Weigh a fraction of an ounce and is 1/2 inch
long
Hands and feet develop. Webbed fingers and toes are fully
formed. Undifferentiated sex organs appear. Teeth buds develop.
Kidneys and liver start functioning. Weighs 1/30 of an ounce and
is 1 inch long.
The Fetal Period
All major systems are formed. Fingers and toes are fully formed.
Eyes can be clearly distinguished. Sex of the fetus can be
determined visually. Fetus responds to external stimulation.
Weighs 1 ounce and 3 inches long.
Mother detects fetal movement. Many reflexes are present.
Fingernails and toenails are formed.
Hair develops on head. Fine downy hair covers the body. Fetus
sucks thumb and hiccoughs.
Eyes open and close. Light and sound are perceived. Fetus
alternates between periods of sleep and wakefulness. Skin looks
ruddy because blood vessels show through the surface. Survival
rate is low if fetus is born. Weighs about 2 pounds and is about
14 inches long.
Organ systems matured further. Fatty layer begins to develop
under the skin. Fetus turns head down in the uterus. Chances of
survival are good if born. Weighs 3-4 pounds and is 16 inches
long.
Organ systems function well. Fatty layer develops further. Weight
increases to about 7-71/2 pounds and length to 20 inches.