Chapter 3 Section 4

1. Chapter 3 Section 4 Heredity: Our Genetic Background Obj: Explain the role of chromosomes and genes in heredity, and evaluate the methods used by psychologists to study the role of heredity in determining traits.

2. Role of Chromosomes and Genes in Heredity Heredity is the transmission of characteristics from parents to offspring. We study this as a means of understanding why people behave as they do. Heredity plays a key role in the development of traits, and psychological disorders.

3. Genes and Chromosomes Genes are the basic building blocks of heredity and 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; some are more complicated and involve combinations of genes.

4. Genes are found in threadlike structures called chromosomes, which 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 chromosome comes from the mother. Each chromosome contains instructions for the development of particular traits in the individual.

5. Researchers have learned that 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. In males, the 23rd pair consists of an X chromosome (so called because of its X shape) and a Y chromosome (because of its Y shape). Females have two X chromosomes, so they always pass an X chromosome on to their offspring.

6. When a child is born without 46 chromosomes in each cell, physical and behavioral disorders may result. One of the most common disabilities of this type occurs when there is an extra, or third, chromosome on the 21st pair. When this happens, a baby will be born with Down syndrome. People with Down syndrome usually have some level of mental retardation and may have heart and respiratory problems.

7. The Nature-Nurture Debate People have debated the role that nature (biological makeup, what we inherit) plays in forming who we are, versus nurture (refers to environmental factors we are exposed to). Most scientists believe that it is a combination of both.

8. The Study of the Role of Heredity Role of heredity in studies through various types of kinship research such as: • Twin Studies – a useful way to learn about nature and nurture. • Adoptee Studies – provide ways of sorting out the effects of nature and nurture. • Twins Reared Apart – a way of finding out that twins reared apart share many of the same mannerisms despite their separation.