Genetic effects on personality
Prof. Roomana N. Siddiqui Chairperson, Dept. of Psychology Aligarh Muslim University
Heredity is the transmission of traits from parents to children and from one generation to another.
The general perception is that everything is heritable but this does not mean that your personality is determined by biological processes.
Similarities and differences in genetic makeup are associated with how close individuals are biologically. Immediate family members have more in common with each other genetically than distant relatives and have less in common with extended families.
You may have noticed that many traits run in families. For instance, members of a family may share similar facial features, hair color or a predisposition to health problems such as diabetes. Characteristics that run in families often have a genetic basis, meaning that they depend on genetic information a person inherits from his or her parents.
Individuals inherit 23 pair of chromosomes from their parents half coming from the mother an half coming from father.
Chromosomes are the carriers of genes that carry the genetic information. It is accepted that genetic differences account for the difference in personality. But we need to further explore how genes contribute to individual differences in the development of personality.
Recent estimates of heritability of personality traits based on twin studies suggests that 30 to 50% of variance in personality is due to genetic factors while the rest is due to environmental factors.
Gregor Mendel a monk got interested in finding out how traits are inherited from parents to children’s.
Example if the mother has blue eyes and the father has brown eyes what colour will be the eyes of the child?
Will it be blue like the mother, or brown like the father or a mix of blue and brown, that is brownish blue eyes?
For hair also if the mother has straight hair and the father has curly hair what will be the texture of hair of the child?
To get the answer to these questions he did experiments but as it was unethical to do it on humans he did it on garden peas.
Mendel took peas having different coloured flowers one white in colour and the other violet. Similarly he did experiments on tall and short pea plants.
He was interested in seeing how physical characteristics are transmitted from parents to children.
He cross bred peas and kept record of them for generations and noted how they were similar or different from parents.
When he cross bred on height he found that in the first generation all the peas were of tall stem (F1 generation). This made him wonder what had happened to the short height peas, had they disappeared. If that was the case then if the F1 generation were cross bred among themselves then we should have only tall height peas.
So he cross pollinated the tall height peas among themselves.
In the second generation he observed that there were some short height peas also along with tall height peas.
For every 1 short height peas there were 3 tall height peas.
In the next generations when he cross pollinated the short height with short height peas he only got short height peas but when he cross pollinated the tall peas with tall peas then he got 1/3rd all tall and of the 2/3rd there were 1 short for every three tall peas. The ratio 1:3 was maintained.
On the basis of his experiment he concluded that:
The inheritance of each trait is determined by something (which we now call genes) passed from parent to offspring unchanged. In other words, genes from parents do not ‘blend’ in the offspring.
For each trait, an organism inherits one gene from each parent.
Although a trait may not appear in an individual, the gene that can cause the trait is still there, so the trait can appear again in a future generation.
On the basis of this finding he discovered the fundamental laws of inheritance. He concluded that genes come in pairs and are inherited as distinct units, one from each parent. He tracked the segregation of parental genes and their appearance in the offspring as dominant or recessive traits.
1. Law of segregation:
Each inherited trait is defined by a gene pair. Parental genes are randomly separated to the sex cells so that sex cells contain only one gene of the pair.
Offspring therefore inherit traits on an all or none basis, that is either have blue eyes or brown and not a mix of them. When two parent cell unite and reproduce each cell provide a gene for a particular characteristics like color of eye. If both parents have blue eyes then the child may have blue eyes but if one parent has blue and the other has brown then which color he child will inherit.
2. Law of Dominant and Recessive genes
An organism with alternate forms of a gene will express the form that is dominant. If in a pair of genes both traits are dominant then like tallness then the peas will have tall peas, if both the traits are short then the offspring will be short but if in the pair one trait is dominant (Tall) and the other is recessive (Short) then the dominant trait will be expressed. It will not be a blending that is average height but offspring will be tall.
Similarly for color brown eyes are associated with dominant genes and blue eyes are associated with recessive and curly hair is dominant and straight hair is recessive.
3. Law of Independent Unit Characters.
Genes for different traits are sorted separately from one another so that the inheritance of one trait is not dependent on the inheritance of another. That is the color of the eyes will not influence heigh or texture of hair or skin color.
Each trait will be inherited according to the first two laws.
Hence children of the same parents have different characteristics because the combinations of chromosomes in each cell is different.
Relationship between genetics and personality is complex
The branch of sociobiology has tried to established that even social behaviour like helping, conformity and cheating have a biological or genetic basis. They were guided by the ideas of Darwin.
Darwin argued that human facial expressions were inherited, for example one shows his teeth when angry, smiles when happy etc.
Research done on facial expression of deaf and blind showed a lot of agreement between cultures and this helped in identifying emotions.
Freedman did a study on blind and deaf children and observed that they showed quite normal facial expression in different cultures. The only difference was that culture plays an important in controlling the facial expression and deciding which situation is appropriate for which emotion.
Friesen and Ekman took six primary emotions---fear, surprise, disgust, anger, happiness and sadness and identified the facial expression in these emotions. He showed these photographs to people in United States, Brazil, Chile, Argentina and Japan. The results showed that there was a high degree of agreement amongst the five emotions. It appears that facial expressions of some emotions are to a great extent genetically determined.
In one study Buss and his colleagues selected four temperament : emotionality, activity, sociability and impulsivity. They found that correlation were higher for identical rather than fraternal twins suggesting that temperament has a genetic component.
Interesting evidence for the effect of biological temperament on temperament comes from the work of Eysenck in the area of introversion- extroversion. Introverts are generally quiet, reserved and thoughtful while extroverts are active, sociable and outgoing. According to him extroverts have very low level of brain arousal so they seek stimulation. Introverts on the other hand are thought to have higher level of central nervous system arousal and so they shy away from stimulating social environments.
