Relative Importance Of Heredity And Environment

This article explains the role of heredity and environment in infants, and about the genes in human beings

The relative importance of heredity and environment or of nature and nurture in determining the personality is an old and much debated question. Some thinkers hold the view that heredity alone determines the personality of an individual. Where as some others are of the opinion that environment plays a significant role in the development of an individual. However we need not take either extreme of this time worn controversy. The individual is influenced by both the factors and hence he is a product of both the influences.


Heredity is the "process of transmitting certain traits - physical and psychological from parents to offsprings through gene".
Each individual is born out of a single fertilized egg of a woman. This egg or cell is smaller than a pin head. The egg or the ovum has a nucleus surrounded by a jelly like substance called cytoplasm. The nucleus has chromosomes which are always found in pairs. These are rod like structures which are present in the same number in all the members of a species. In human beings there are 46 chromosomes. In human females there are 23 pairs, where as males have 22 pairs and two singles of which one is x and another is y. It is this last pair which determines the sex of the individual. The female egg contains only xx chromosomes as it's last pair.
The heredity factors in the germ cell which shape the constitution and behaviour of the developing individual are called Genes. Genes are minute but definite particles located in the chromosomes. They are beed like structures which determine the various physical and psychological traits of an individual. Therefore the genes are called true carriers of heredity. A recent work has placed the number of genes in human beings at about forty thousand.
The chemical make up of genes shows that there are two important chemical substances namely D.N.A and R.N.A. The structure of D.N.A or de-oxyribo nucleic acid is believed to contain certain genetic information in coded form. At appropriate times in the development of the cells, this information is communicated to determine the course of further development.

Recessive and dominant genes

Geneticists have discovered that the recessive genes remain latent and fail to appear in the offspring when supressed by the dominant genes. For example if gene A indicates brown eyes and is dominant and gene "a" which is blue eyes is recessive. The offspring would be brown eye.
The original fertilized cell divides into two each of these again into two and so on. In this way the organism grows and develops. Each individual receives 23 chromosomes fro the mother and 23 from the father so that half his genes come from one parent and half from the other. In a general way we may say that one half of our biological inheritance derives from each parent, 1/4th from each grand- parent, 1/8th from each great grand parents and so on.
Two processes : Meosis and mitosis


Meosis is a reduction process which takes place to reduce the number of chromosomes fro 46 to 23. It takes place in the re - productive organs that is testes of the male and ovaries of the females. This reduction process is known as germ cell maturation or mesis. It is only after this, the ripened cell is expelled from the ovary to facilitate fertilization. The fusion of the male and the female cells constitutes fertilization or conception. The organism which is the resultant of this fertilization is known as zygote


This is cell multiplication or duplication process. This takes place after fertilization. Though the cells multiply the number of chromosomes in each cell remains the same. This multiplication process takes place in geometrical ratio. Following this process formation of the layers takes place. The three layers are endoderm (inner most layer), mesoderm (middle layer) and ectoderm (outer layer) from these layers different structures of the organism namely bones, muscles nerves emerge.

Identical and fraternal twins

The twins develop out of a single zygote are known as monozygous or identical twins. As they share the same chromosomes, the sex of both the twins will be the same. They closely resemble each other in physical and mental characteristics.
Sometimes two ova are released by the ovary. If both are fertilized simultaneously by two sperms two individual emerge and grow into twins. Such (twins who are born out of two separate ova are known as di - zygous or fraternal twins). They are not similar to each other because they carry two different hereditary units. They may be of the same sex or different.


Siblings are brothers and sisters born with a gap of time, but each is different from the other ot only in sex but in many other characteristics because there hereditary endowments are different from each other.

Parental period

This is the duration of time between conception and birth. This period is divided into three stages namely
1.Period of ovum
2.Period of embryo
3.Period of foetus


The term environment covers many factors. Environment means that which immediately surrounds on individual but in psychology the term environment is used to refer to those stimuli or factors which act upon the individual environment can broadly be classified into two namely external and internal.
The external environment can further be classified into social and physical. The social environment includes factors such as religion, family, culture, customs etc where as the physical environment includes factors such as water, air, food, shelter etc. The internal environment is further divided into two intra cellular and the internal environment is that environment prior to the birth of a child the cytoplasm is considered as an intra cellular environment the various chemicals that are present inside the cell are also included under the environment. The inter cellular environment includes the food various other substances that are consumed by mother. If the mother is in the habit of smoking or drinking or taking drugs it has a direct impact on the growth of the child. Therefore internal environment is very important in determining the development of the child.

Relative importance of heredity and environment

To study the role of heredity in the development of an individual, the environment has to be kept constant, heredity should be varied. If any difference in behaviour is found, it should be attributed to the heredity. On the other hand in the role of environment, heredity has to be kept constant and environment should be varied. The differences in behaviour have to be attributed to the environment.

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