This document discusses heredity and environment and their roles in personality, intelligence, and behavior. It covers several key points: 1) Heredity involves the transmission of traits from parents to offspring through genes and chromosomes. Traits like physical characteristics and mental abilities are influenced by genes. 2) The environment, both prenatal (mother's health/habits) and external after birth (family, socioeconomics, climate), shapes development and has lasting effects on individuals. 3) Studies of twins suggest traits like temperament are influenced by both heredity and environment, as identical twins share more similarities than fraternal twins. However, neither factor alone can determine behavior, which arises from their interaction

1. Heredity & Environment
For Physiotherapy and Nursing students

2. Heredity
• Heredity is the transmission of characteristics through genes from parents to
offspring's. These are both mental and physical characteristics, which include
intelligence, personality etc.,
• At the time of conception 23 chromosomes from father and 23 chromosomes
from mother are transmitted to the offspring's.
• Male (22 autosomes + XY)
• Female (22 autosomes + XX)
• If the offspring gets XX chromosome pair, that will be female and if it is XY then it
will be male.
• The offspring gets the physical characteristics such as height, weight, skin texture,
vision, hair and mental characteristics such as intelligence, temperament and so
on by the genes carried by the chromosomes.
• These genes contain two chemical substances, named DNA and RNA, which are
said to be responsible for carrying out the genetic code message from parent to
offspring.

3. • Transfer of traits:
• According to Gregor Mendel, some genes are dominant and others recessive.
Like chromosomes, genes also occur in pairs. Each of the pair is donated by
one of the parents.
• Forms of Gene Pair:
• A dominant gene from one parent and recessive gene from the other.
• Dominant genes from the both parents.
• Recessive genes from both parents.
• Determinations of sex:

4. • Twins mechanism:
• Life is the result of union of two cells—male and female. Normally when a single
ovum is fertilized by sperm cell of the male, it results in the birth of a single
offspring. However, in some cases, this normal function is disturbed and there
are cases of multiple births, There are two distinct types of twins:
• Identical Twins:
• During the process of fertilization of the ovum by the sperm, the ovum is made
to split into two parts but unite later. If this fails, that grows separately and leads
to twins.
• They are called as identical twins because of the genetic material (same
chromosomes and genes). They are found to possess almost the same somatic
structure and characteristics and are definitely of the same sex.
• Fraternal twins:
• In an exceptional case, two ova may be produced simultaneously and be
fertilized at the same time by two different sperms. So two individuals may be
growing simultaneously in the womb of the mother. They are known as fraternal
twins.
• They have different combination of chromosomes and genes, so they are sure to
differ in many traits. They may have similar or opposite sex.

5. Laws of Heredity
• Law of similarity: According to this law, children tend to be similar to their
parents. Thus, children of fair-coloured parents will be fair-coloured and
visceversa.
• Regarding inheritance of intellectual properties, the bright parents likely to
have bright children, average parents tend to have average children.
• Thus similarity law may work well for explaining the transfer of so many traits
and characteristics from parents to offspring's.
• Law of variation: According to this law, children may vary or differ from their
parents in relation to one or the other traits or characteristics.
• The reason for such variations lies in the characteristics of the germ cells of
the parents. Germ cells contain many determiners which are, responsible for
transmission of hereditary characteristics to offspring's.

6. Environment
• According to Woodworth, Environment covers all the outside factors that
have acted on the individual since he began life.
• The hereditary plays its game only at the time of conception. Afterwards the
environment affects the individual, his bodily structure and all of his
personality make-up and behaviour.
• Types of Environment There are two types of environment, which are as
follows:
• Internal environment/Pre-natal (Conception to till birth—9 months).
• External environment/Post -natal (After birth).

7. Internal Environment
• The embryo receives nutrition through blood stream of his mother.
• The physical and mental health of the mother including her habits, attitudes and
interest, etc. all constitutes the inner surroundings that affect the growth and
development of the individual.
• The growth and development are more rapid inside the womb than any other time in
the life.
• Proper antenatal care should be given like high calorie, high protein diet,
immunization, rest and sleep, regular check-ups, follow-up visits, preparation for
delivery etc.,
• The mechanical problems of the antenatal such as suffering from instrumental
delivery, obstructed labors may cause defects in newborn.
• Mother suffering from metabolic disorders, endocrinal disorders, habits like smoking,
drinking, drug abuse, Psychological hazards etc., may lead to prematurity or deformity
of child.

8. External environment
• The external environment has following components, which are as follows:
• Physical environment—Earth, rivers, mountains, wealth, food, water, etc.
• Social or cultural environment—Parents, family members, friends, classmates,
neighbors, teachers, communication, recreation, religious places, clubs, libraries.
• Socio- economic status- Low social standards and low economy leads to
morbidity and mortality among children.
• Climate and seasons: Seasonal variations varies the activity levels of children.
Climatic conditions will influence growth rates.
• Ordinal position in the family: The first-born child will receive all parental
attention until the second child is born. The first born, maybe raised rigidly and
with anxiety.
• Birth order research focuses on five ordinal birth positions: First born,
second born, middle and last

9. Role of Heredity and Environment on Personality, Intelligence
and Behaviour
• The role of nature has been extensively searched in the form of twins and family studies and
experiments on selective breeding.
• The results of all studies have failed to establish a clear-cut role of either heredity or
environment in explaining the presence of particular behaviour or trait in an individual. So
development of a personality trait is always a result of interaction of the environmental
forces on the genetically inherited characteristics.
• Theories: (Passivity vs Activity)
• John.B.Watson describes that the child as raw material waiting to be shaped by parents
and others.
• B.F. Skinner describes human behaviour and development as a process of responding to
rewards and punishment in the environment. (Passivity)
• In the other Piaget argued that we actively manipulate the objects and events around us.
We construct our own ways of understanding the world.

10. • Heredity on Personality:
• Psychologists are still trying to learn how much genes influence personality.
• Studies on Temperament:
• Temperament includes mood, activity level, emotion and variability of each. Studies
with animals have shown that selective breeding can heighten or diminish
characteristics like emotionality, over successive generation.
• In one of the studies, mother of (monzygotic) identical twins and (dizygotic) fraternal
twins were asked to fill out temperament questionnaires about their children. Each
mother rated child on four dimensions such as:
• Emotionality.
• Activity.
• Sociability.
• Impulsivity.
• On all four dimensions correlation were higher for identical twins than fraternal twins.
Since identical twins have 100 % identical genes while fraternal twins have only 50 %.
So this study supports the notion of genetic influence.

11. • Traits, Types and Chromosomes:
• These are evidences to contribute that a large number of adult traits have
genetic influence. Eysenck H.J. proposed that the traits related to
introversion, extroversion type.
• Dimensions are linked to reticular formation that is of the part of the brain
that influences an individual’s level of arousal.
• Tests of extroversion and introversion have shown fairly strong evidence of
hereditability.
• Conclusion:
• The genetic potentials can only be expressed by interacting with the
environment or nurture. So the human behaviour actually observed results
from the interaction of nature and nurture

12. Thank you..!