Genetics and Behavior – Psychology – UGC NET – Notes

Behaviour genetics, also known as psychogenetics, is the study of how an organism’s genetic composition influences its behaviour, and how heredity and environment interact to shape behaviour.

The question of what determines behavioral abilities and disabilities is often referred to as the “nature-nurture controversy”, which examines the relative influence of genes (nature) and environment (nurture) on behaviour.

Early History

The relationship between behaviour and genetics (heredity) dates back to the work of Sir Francis Galton (1822–1911), who coined the phrase “nature and nurture.” Galton studied families of outstanding individuals and concluded that mental abilities run in families, similar to the ideas of his cousin Charles Darwin. He was also the first to use twin studies in genetic research and developed important statistical methods still used today.

In 1918, Ronald Aylmer Fisher demonstrated how Mendel’s laws of inheritance apply to complex traits influenced by both multiple genes and environmental factors. Early research on human behaviour, especially intelligence and mental illness, began in the 1920s, during a time when environmentalism (the belief that behaviour is shaped mainly by environment) was widely accepted.

However, the misuse of genetics during Nazi Germany made ideas about heredity controversial. Despite this, research continued, and by the 1970s, a more balanced understanding emerged, recognizing the importance of both nature and nurture. In psychology, this balance became widely accepted in the 1980s.

Today, behavioral genetic research focuses on identifying specific genes that influence personality, intelligence, and disorders such as autism, hyperactivity, depression, and schizophrenia.

Methods Of Study

Quantitative genetic methods are used to estimate the effects of both genetic and environmental factors on individual differences in complex traits, including behaviour. In addition, molecular genetic methods help identify specific genes responsible for these influences. Research is conducted on both animals and humans, though animal studies often provide more accurate and controlled data.

By mating related animals over generations, scientists create inbred strains that are genetically similar. This allows researchers to study genetic influence on behaviour by comparing animals raised in the same environment. Another method, known as selective breeding, involves breeding individuals with extreme traits over generations to observe genetic effects. These methods have been widely used to study behaviours like learning and drug responses, showing strong evidence of genetic influence.

In humans, since genes and environments cannot be directly manipulated, researchers use quasi-experimental methods. One important method is the twin method, which compares monozygotic (MZ) twins and dizygotic (DZ) twins. MZ twins are genetically identical, while DZ twins share about 50% genetic similarity, like regular siblings.

If behaviour is influenced mainly by the environment, both MZ and DZ twins should show similar levels of resemblance. However, if genetic factors play a role, MZ twins will be more similar than DZ twins. For example, in schizophrenia, the concordance rate is about 45% in MZ twins and 15% in DZ twins. For intelligence (IQ), the correlation is around 0.85 for MZ twins and 0.60 for DZ twins.

Thus, the twin method is considered a reliable tool for estimating the genetic influence on behaviour, even though it provides only a rough approximation.

Chromosomal Abnormalities

Almost every cell in our body contains 23 pairs of chromosomes (a total of 46). Half of these come from the mother and half from the father. The first 22 pairs are called autosomes, while the 23rd pair consists of the sex chromosomes (X and Y). Females typically have XX, while males have XY chromosomes.

All the information required for growth and development is stored in these chromosomes. Each chromosome contains thousands of genes, which produce proteins that regulate body functions and chemical processes.

There are two main types of chromosomal abnormalities: numerical abnormalities and structural abnormalities. Numerical abnormalities involve extra or missing chromosomes, while structural abnormalities involve changes in chromosome structure, such as missing or rearranged segments. These abnormalities can occur during the formation of egg or sperm cells or early fetal development. Factors like maternal age and environmental influences may increase the risk.

Chromosomal abnormalities can lead to various effects such as miscarriage, diseases, or developmental problems. One well-known example is Down syndrome (trisomy 21), caused by an extra copy of chromosome 21. The most common type of abnormality is aneuploidy, where there is an abnormal number of chromosomes. Examples include trisomy 18, trisomy 13, Turner syndrome (45, X), Klinefelter syndrome (47, XXY), XYY, and XXX conditions.

Structural abnormalities result from breakage and incorrect rejoining of chromosome segments. These can include deletions, duplications, insertions, ring chromosomes, and isochromosomes. Structural changes may be balanced (no genetic material lost or gained) or unbalanced (extra or missing genetic material).

Even balanced rearrangements may sometimes cause disease if they disrupt a gene or create a faulty protein. Thus, chromosomal abnormalities can significantly affect health and development, depending on their type and severity.