UNIT 2 PRENATAL DEVELOPMENT
(GENETICS, ENVIORNMENT
INFLUENCE AND HAZARDS OF
DEVELOPMENT)
Structure
2.0 Introduction
2.1 Objectives
2.2 Beginnings of the Life
2.3 Characteristics of Prenatal Period
2.4 Period of Prenatal Development
2.4.1 Period of Zygote
2.4.2 Period of Embryo
2.4.3 Period of Fetus
2.5 Environmental Influences
2.6 Let Us Sum Up
2.7 Unit End Questions
2.8 Suggested Readings and References
2.9 Answers to Self Assessment Questions
2.0 INTRODUCTION
Prenatal development is the process in which an embryo or fetus, gestates during
preganancy, from fertilisation until birth. Often, the terms fetal development, foetal
development are used in a similar sense.Most physiologists and members of the
medical profession believed that most development takes place before birth.
Development before birth takes place in three stages or period’s i.e. ovum, embryo
and fetus. Many factors are considered to understand the behaviour of a developing
child. Mainly five factors are considered:
1) Genetically determined biological variables
2) Nongenetically determined biological variables (i.e., lack of oxygen during the
birth process and malnutrition)
3) The child’s past learning
4) The immediate socio psychological environment (parents, siblings, peers and
teachers)
5) The social and cultural milieu in which the child develops.
We always considered biological and environment separately for ease of exposition
but they always act in unison. This is as true of the individual cell as it is of the whole
person. The science of genetics and embryology has shown dramatic progress during
the last 25 years. This unit will deal with the current knowledge of human genetics
20 and prenatal factors affecting the course of development. In this unit you will be able
, to understand the major happenings during the nine months of prenatal developement Prenatal Development
(Genetics, Enviornment
and what genetics, environmental influence and hazards affect the course of Influence and Hazards of
development. Development)
2.1 OBJECTIVES
After going through this unit, you will be able to:
z explain the concept and characteristics of the prenatal period;
z describe the stages of prenatal period;
z point out the genetic factors;
z describe the attitudes of significant people towards the child; and
z analyse the common physical hazards in each subdivision of the prenatal period.
2.2 BEGINNINGS OF THE LIFE
The new life begins with the combination of a male sex cell and female sex cell. The
development of each individual begins when a sperm cell from the male penetrates
the wall of an ovum, or egg, from the mother. These sex cells are developed in the
reproductive organs. For example, the male sex cells are produced in the male
gonads, the testes, while the female’s sex cells are produced in the female gonads,
the ovaries. Development begins at conception. At the moment that the tiny Tadpole-
shaped sperm penetrates the wall of the ovum, it releases 23 minute particles called
chromosomes. At approximately the same time, the nucleus, the inner core of the
ovum, breaks up, releasing 23 chromosomes of its own, so that the new individual
begins life with 46 chromosomes.
All the child’s biological heritage from the father and mother is contained in these 23
pairs of chromosomes. Of these pairs, 22 are autosomes, possessed equally by
males and females. The 23 pair, the sex chromosomes, differs in males and females.
It is these chromosomes that determine a child’s sex. A female will have two X
chromosomes (XX), while a male has an X and Y chromosomes (XY).
Male and female sex cells also differ in two important ways. First, in the mature
ovum there are 23 matched chromosomes while in the mature spermatozoa there are
22 matched chromosomes and one unmatched chromosome which may be either an
X or a Y chromosomes. The X and Y chromosomes are the sex determinant
chromosomes. The mature chromosome ovum always contains an X chromosome.
If it is fertilised by a Y-bearing spermatozoa, the offspring will be a boy. If it is
fertilised by an X-bearing spermatozoa, the offspring will be a girl.
Once the male and female cells have united, nothing can be done to change the sex
of the newly formed individual. Whether this individual is male or female has a lifelong
effect on the individual’s patterns of behaviour and personality. The question arises
why the sex of an individual is important to lifelong development. The answer of this
question consists of three points, viz. the following:
i) Each year children come under increasing cultural pressure from parents, teachers,
their peer group and society at large to develop attitudes and behaviour patterns
that are considered appropriate for members of their sex. Children who learn
to behave in ways that are considered appropriate for their sex are assured of
social acceptance. 21
(GENETICS, ENVIORNMENT
INFLUENCE AND HAZARDS OF
DEVELOPMENT)
Structure
2.0 Introduction
2.1 Objectives
2.2 Beginnings of the Life
2.3 Characteristics of Prenatal Period
2.4 Period of Prenatal Development
2.4.1 Period of Zygote
2.4.2 Period of Embryo
2.4.3 Period of Fetus
2.5 Environmental Influences
2.6 Let Us Sum Up
2.7 Unit End Questions
2.8 Suggested Readings and References
2.9 Answers to Self Assessment Questions
2.0 INTRODUCTION
Prenatal development is the process in which an embryo or fetus, gestates during
preganancy, from fertilisation until birth. Often, the terms fetal development, foetal
development are used in a similar sense.Most physiologists and members of the
medical profession believed that most development takes place before birth.
Development before birth takes place in three stages or period’s i.e. ovum, embryo
and fetus. Many factors are considered to understand the behaviour of a developing
child. Mainly five factors are considered:
1) Genetically determined biological variables
2) Nongenetically determined biological variables (i.e., lack of oxygen during the
birth process and malnutrition)
3) The child’s past learning
4) The immediate socio psychological environment (parents, siblings, peers and
teachers)
5) The social and cultural milieu in which the child develops.
We always considered biological and environment separately for ease of exposition
but they always act in unison. This is as true of the individual cell as it is of the whole
person. The science of genetics and embryology has shown dramatic progress during
the last 25 years. This unit will deal with the current knowledge of human genetics
20 and prenatal factors affecting the course of development. In this unit you will be able
, to understand the major happenings during the nine months of prenatal developement Prenatal Development
(Genetics, Enviornment
and what genetics, environmental influence and hazards affect the course of Influence and Hazards of
development. Development)
2.1 OBJECTIVES
After going through this unit, you will be able to:
z explain the concept and characteristics of the prenatal period;
z describe the stages of prenatal period;
z point out the genetic factors;
z describe the attitudes of significant people towards the child; and
z analyse the common physical hazards in each subdivision of the prenatal period.
2.2 BEGINNINGS OF THE LIFE
The new life begins with the combination of a male sex cell and female sex cell. The
development of each individual begins when a sperm cell from the male penetrates
the wall of an ovum, or egg, from the mother. These sex cells are developed in the
reproductive organs. For example, the male sex cells are produced in the male
gonads, the testes, while the female’s sex cells are produced in the female gonads,
the ovaries. Development begins at conception. At the moment that the tiny Tadpole-
shaped sperm penetrates the wall of the ovum, it releases 23 minute particles called
chromosomes. At approximately the same time, the nucleus, the inner core of the
ovum, breaks up, releasing 23 chromosomes of its own, so that the new individual
begins life with 46 chromosomes.
All the child’s biological heritage from the father and mother is contained in these 23
pairs of chromosomes. Of these pairs, 22 are autosomes, possessed equally by
males and females. The 23 pair, the sex chromosomes, differs in males and females.
It is these chromosomes that determine a child’s sex. A female will have two X
chromosomes (XX), while a male has an X and Y chromosomes (XY).
Male and female sex cells also differ in two important ways. First, in the mature
ovum there are 23 matched chromosomes while in the mature spermatozoa there are
22 matched chromosomes and one unmatched chromosome which may be either an
X or a Y chromosomes. The X and Y chromosomes are the sex determinant
chromosomes. The mature chromosome ovum always contains an X chromosome.
If it is fertilised by a Y-bearing spermatozoa, the offspring will be a boy. If it is
fertilised by an X-bearing spermatozoa, the offspring will be a girl.
Once the male and female cells have united, nothing can be done to change the sex
of the newly formed individual. Whether this individual is male or female has a lifelong
effect on the individual’s patterns of behaviour and personality. The question arises
why the sex of an individual is important to lifelong development. The answer of this
question consists of three points, viz. the following:
i) Each year children come under increasing cultural pressure from parents, teachers,
their peer group and society at large to develop attitudes and behaviour patterns
that are considered appropriate for members of their sex. Children who learn
to behave in ways that are considered appropriate for their sex are assured of
social acceptance. 21
