This is the 2007 version. Click here for the 2017 chapter 10 table of contents.

Summary: Genetic Influences

The word gene is a shorthand term for a pattern of chemicals called bases on the double helix of the DNA molecule. The sequence of bases determines the construction of a molecule such as a protein. Chromosomes an be seen in a karyotype. They contain about 20,000 active genes. Fifty percent of a person's genes come from the mother and fifty percent from the father, but grandparents can contribute more or less than twenty-five percent.

Many psychologists dislike the idea of "nature versus nurture" because these are not two opposing forces. Genetic control is required for any biological system, but this can only take place in an environment, and the environment can alter the way the genes are expressed.

The heritability index is based on measuring some trait in identical twins and comparing the correlation with the same trait measuring in fraternal twins. A trait with a high heritability index is more likely to be similar in identical twins. However, even behaviors that are clearly not passed down in the genes (like TV watching) have a high heritability index, so a high heritabiliy index should not be interpreted as proof that a trait is somehow coded into a person's DNA.

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