Psychology Chapter 3 Section 4: Heredity: Our Genetic Background

Heredity is the transmission of characteristics from parents to offspring. Psychologists are interested in studying heredity, along with the brain and hormones, as a means to understanding how and why people behave as they do.

Heredity is vital in the transmission of physical traits such as height, hair texture, and eye color.

Researchers have found that some psychological traits such as shyness, leadership, aggressiveness, and even an interest in arts and crafts are influenced by heredity.

Heredity has been shown to be one factor involved in many pshcological disorders including… Anxiety Depression Schizophrenia Bipolar disorder Alcoholism

Genes and Chromosomes Genes are the basic building blocks of heredity. Traits are determined by pairs of genes, with one gene in each pair inherited from each parent. Some traits, such as blood type, are controlled by a single pair of genes. Complex psychological traits, such as intelligence, involve combinations of genes, as well as environmental factors.

Genes are found in threadlike structures called chromosomes.

Chromosomes are composed of deoxyribonucleic acid (DNA). DNA takes the form of a double helix.

Most normal human cells contain 46 chromosomes that are organized into 23 pairs. In each of the 23 pairs, one chromosome comes from the father and the other chromosomes comes from the mother. Each chromosome contains instructions for the development of particular traits in the individual.

22 of the 23 pairs of chromosomes are similar in males and females. The 23rd pair, the sex chromosomes, determines whether we are female or male. XY Male XX Female

The chromosomes that comes from the father determines the sex of the offspring.

When a child is born without 46 chromosomes in each cell, physical and behavioral disorders may result. Down syndrome Extra or third chromosome on the 21st pair.

The Nature-Nurture Debate Nature refers to what people inherit. Nurture refers to environmental factors. Today, most psychologists agree that the influences of both nature and nurture determine our psychological traits.

Kinship Studies Degree to which people are related, based on the genes they have in common. Identical twins share 100 percent of their genes. A parent and his or her child share 50 percent of their genes, as do full brothers and sisters. Aunts and Uncles related by blood share an average of 25 percent of their genes with nieces and nephew, and first cousins share an average of 12.5 percent.

Psychologists use this information to determine how much a trait is influenced by genetics and how much by environment. People who share more genes should be more likely to exhibit the same trait.

Two common types of kinship studies. 1. Twins 2. Adoptee

Twin Studies Identical twins Share the same genetic makeup Differences must be the result of environment

Fraternal Twins Share, on average, 50 percent of their genes. Differences between fraternal twins must stem from heredity or the environment.

Researchers have found that identical twins resemble one another more strongly than fraternal twins in certain traits including… Shyness Activity levels Irritability Sociability These traits appear to be influenced by heredity.

Identical twins are also more likely than fraternal twins to share psychological disorders such as autism, substance dependence, and schizophrenia. In one study on autism 96 percent of both identical twins were likely to be autistic Only 24 percent of both fraternal twins were likely to be autistic. This evidence strongly suggests a role for heredity in autism.

Adoptee Studies Psychologists look for the relative similarities between children and their adoptive and biological families.

Twins Reared Apart Thomas Bouchard Examined twins who were reared apart. Found that many psychological and personality traits including intelligence, traditionalism, risk avoidance, aggression, and leadership are influenced by heredity.