Heredity and environment both play a role in shaping human beings. Heredity refers to biologically inherited characteristics received from parents, influencing physical and behavioral traits. The environment includes prenatal conditions in the womb and postnatal factors like family, society, and culture that one is exposed to. While heredity sets limits, the environment helps reach an individual's potential, as both work together in development.

1. INFLUENCE
OF
HEREDITY
AND
ENVIRONMENT

2. INTRODUCTION
 All human beings are a product of HEREDITY
and ENVIRONMENT.
 Heredity and environmental factors together
play a vital role in shaping human beings.
 Psychologists commonly refer to heredity as
“NATURE” and environment as “NURTURE”.

3. ROLE OF HEREDITY
 Heredity refers to our biologically inherited
characteristics.
 In common words heredity refers to
characteristics that we get from our parents.
 Our physical characteristics such as the color
of the skin, shape of the nose, color of eyes are
inherited from parents.
 Besides influencing our physical
characteristics, heredity also influences our
“BEHAVIOUR”.

4. THE MECHANISM OF
HEREDITY
 The true beginning of human being is a
“SINGLE SECOND EVENT.”
 A human being is conceived when a single
sperm (male reproductive cell) from the
father‟s body fertilizes the ovum (female
reproductive cell or egg) from the mothers
body to form a “Zygote.”
 This process is called “Fertilization” in which a
sperm and ovum combine to create a single cell
called “Zygote.”

5.  Which sperm meets which ovum is of critical
importance as it will determine the sex,
appearance and several other characteristics of
the new life.
 The sperm is one of the several million sperm cells
produced in the father‟s body and the ovum is one
of the several thousands ova produced in the
mother‟s body.

6. CHROMOSOMES
 The zygote consists of 46
chromosomes, half from
each parent.
 That is the zygote
receives 23 chromosomes
from the father (sperm)
and 23 from the mother
(ovum).
 Each chromosome
contains “Thousands of
Genes.”
 This discovery is
credited to “GREGOR
MENDEL.”

7. GENES
 GENES are made of a
complex chemical
substance called the
DNA (Deoxyribonucleic
Acid.)
 Each gene has a different
role to play.
 They go on to become
different structures of
the human body from
the skin, muscle and
other tissues of the body
such as heart, lungs, eyes
etc..

8. The genes that we get from our parents are purely
a matter of “Chance.”
This is the reason why two children of the same
parents are so different (except in the case of
identical twins.)
Studies have found that there is almost a 50%
difference in the genes of Brothers and Sisters.

9. They are basic units of heredity.
Genes are structures present on the chromosomes.
Genes are only responsible for passing of heredity
traits from one generation to another.
Hence, Genes are commonly known as “Carriers of
Heredity.”

10. CLASSIFICATION OF
GENES
GENES
Dominant Genes Recessive Genes

11. A) DOMINANT GENES
 A gene whose effect
shows up in a child,
whether or not, it is
paired with a similar
type of gene is called a
“Dominant Gene.”
 For example, If a child
receives a gene for blue
eyes from the father and
brown eyes from the
mother, then the child
will have „brown eyes.‟
This is because, the gene
for the „brown eyes‟ is a
dominant gene.

12. B) RECESSIVE GENES
 A Recessive Gene is one
whose effect shows up
only and only when it is
paired with one just like
itself.
 It will not reveal its
characteristics when it is
paired with a dominant
gene.
 For example, the gene for
blue eyes is a recessive
gene. It will express its
characteristics only when
it is paired with another
gene for blue eyes.

13. DETERMINANTS OF THE
SEX OF THE CHILD
 The zygote consists of 46 chromosomes.
 These 46 chromosomes are arranged in 23
pairs.
 Out of these 23 pairs, the first 22 pairs are
called “Autosomes” or “Non-sex
chromosomes.”
 The 23rd pair is called the “Sex chromosome.”
 This pair determines whether the new human
being will be a male or a female.

14.  Sex chromosomes are
either “X” or “Y”
chromosomes.
 The ovum always
contributes an X
chromosome.
 The sperm may
contribute an X or a Y
chromosome.
 When the zygote formed
is „XX‟, a Female child
will be born.
 When the zygote formed
is „XY‟, a male child will
be born.

15. Thus, the sex of the child depends entirely on the
sperm whether it contributes an X or a Y
chromosome.
And hence,“it is the father who is solely
responsible for the sex of the child.”
But due to ignorance in our Indian Society, there is
tremendous pressure on the woman to give birth to a
male child.
This is indeed sad because it is the father‟s sperm
that determines a child‟s sex.

16. TWINS

17. A) MONOZYGOTIC TWINS
 Monozygotic Twins
develop from a “Single
Fertilized Egg.”
 In the case of these
twins, the zygote splits
into “Two Halves.”
 They are commonly
known as “Identical
Twins.”
 They are of the same sex
and look alike.

18. B) DIZYGOTIC TWINS
 Dizygotic Twins develop
from two separate
zygotes.
 They are commonly
known as “Fraternal
Twins.”
 They are developed from
different sperms and are
„siblings‟ born at
different times.
 They may or may not be
of the same sex and they
do not look alike.

19. ROLE OF THE
ENVIRONMENT
 The term “Environment” refers to all external
events or conditions to which an individual is
exposed.
 It is the world or society in which we are born
and brought up.
 Environment includes both Prenatal and
Postnatal conditions.
 Prenatal conditions are before birth and
Postnatal are after birth conditions.

20.  Before birth, the individual develops in the
environment of his mother‟s womb.
 So everything that happens to a woman during
pregnancy can affect the child.
 After birth, he is affected by the environment
which consists of the outside world, family,
school, peers and culture.

21. A) PRENATAL
ENVIRONMENT
 The “Prenatal Environment” refers to the
environment before birth.
 Some of the factors that affect the Prenatal
Environment are:
i. Prenatal Nourishment
ii. a) Drug Intake
b) Smoking
iii. Mother‟s Health
iv. Medical X-rays
v. Mother‟s Age
vi. Environmental Hazards

22. i. PRENATAL
NOURISHMENT
 Babies develop best
when the mothers eat
well.
 A woman‟s diet before
as well as during
pregnancy is crucial to
her child‟s future.
 A pregnant woman
should have a well
balanced diet.
 It must include proteins,
dairy products, bread,
cereals, and fruits and
vegetables rich in
Vitamin C.

23. ii. a) Drug Intake
 Everything that a
mother takes finds its
way to a new life.
 A pregnant woman must
not take any medication
without consulting a
doctor.
 Drinking alcohol can
also harm the “Fetus.”
 It can lead to Fetal
Alcohol Syndrome
(FAS).
 FAS causes slow
prenatal and postnatal

24. b) Smoking
 Smoking during
pregnancy is the cause of
poor fetal growth.
 Pregnant smokers give
birth to small babies.
 Smoking during
pregnancy can cause
bleeding during
pregnancy and death of
the fetus or newborn.

25. iii. Mother’s Health
 Illnesses suffered by a pregnant woman can
have serious effect on the developing fetus.
 How serious the effects are, depends on the
level of sickness of the pregnant woman.
 Sexually Transmitted Diseases (STD) and
diseases such as measles can have terrible
effects on the health of the baby.

26. iv. Medical X-rays
 Exposure to X-ray
radiations can cause
gene mutations.
 Gene mutations are
minor changes that alter
a gene to produce a new
harmful characteristic.
 Exposure to radiations
should be avoided
especially during the
first three months.

27. v. Mother’s Age
 A woman‟s age at the time of pregnancy is also
an important factor.
 Older pregnant women are more likely to
suffer complications.
 There is a greater risk of miscarriage,
premature delivery, retarded fetal growth to
older women.
 Women over the age of 35 are at the greatest
risk.

28. vi. Environmental Hazards
 Exposure to chemicals, radiations, extremes of
heat and humidity can affect prenatal
development.
 Exposure to nuclear radiations are extremely
dangerous.
 It increases the risk of mental retardation and
is the cause of smaller head size and
chromosomal abnormalities.

29. Postnatal Environment
 The postnatal environment refers to the
environment after birth.
 It is also known as “External Environment”.
 The postnatal environment can be broadly
classified into 3 areas:
i. Physical environment
ii. Social environment
iii. Cultural environment

30. i. Physical Environment
 The physical
environment into which
an individual is born,
has a significant impact
on the individual‟s
growth and
development.
 The geographical
conditions of the region
also have an impact on
an individual‟s
development.

31.  The physical environment includes the
availability of food, clothing and shelter. Poor
nourishment and diet have negative effects on
an individual‟s height, weight, eyesight and
even mental development.

32. ii. Social Environment
 The social environment
is the society in which an
individual is born and
brought up.
 It includes the family,
school, peers,
neighborhood, to which
an individual is strongly
exposed.
 The individual is
strongly affected by the
kind of experience he
has in his social
environment.

33. iii. Cultural Environment
 Culture refers to
customs and ways of
behavior that are
common to a society.
 It is a society‟s or a
group‟s total way of life.
 It includes customs,
traditions, beliefs,
values, language, passed
on from parents to
children.

34. NATURE VERSUS
NURTURE
 Psychologists differ with
regards to the
importance they give to
nature and nurture.
 However in reality, both
heredity and
environment interact
with each other to
influence the
development of the
individual.

35. Heredity sets limits and environment helps the
individual reach the limits.
Heredity factors produce their effects under the
conditions provided by the environment.