chromosome pair, and the child will be a female. On the other hand, if a Y type sperm fertilises the egg, the 23rd chromosome pair will be XY, and the child will be a male. Chromosomes are composed mainly of a substance called Deoxyribonucleic Acid (DNA). Our genes are composed chiefly of DNA molecules.
The two genes that control the development of each trait are situated at the same locus, one on each chromosome of a particular pair. The exception is the sex chromosomes, i.e. the pair of chromosomes that determines an individual’s sex. other behavioural traits).
The traits, which can be passed on to the offspring through genetic material are called its genotype. All biological and psychological characteristics that a modern man possesses are the result of genotype inheritance with phenotypical variations. A given gene can exist in several different forms. Change of a gene from one form to another is called mutation .
The type of mutation that occurs spontaneously in nature provides variation in genotypes and permits the evolution of new species. Mutation permits recombination of new genes with the genes already present. This new combination of genes structure is then put to test in the environment, which can select out those genotypes that turn out to be best fitted for the environment. C ULTURAL B ASIS : S OCIO -C ULTURAL S HAPING OF B EHAVIOUR After reading the biological basis of behaviour you may have developed an idea that many of our behaviours are influenced by hormones and many others occur as reflexive responses.
However, hormones and reflexes do not explain all of our behaviour. The hormones play an important role in regulating human physiology, but they do not completely control human behaviour. Similarly stereotype (fixed pattern), which is the most distinguishing feature of a reflex, does not appear with most human responses. We can draw examples from several domains of our life to argue that our behaviour is more complex than the behaviour of animals.
A major reason for this complexity is that unlike animals, human beings have a culture to regulate their behaviour.