Chapter 3 – Biology and Behavior Section 4 Heredity: Our Genetic Background adapted from the Holt textbook by Mrs. Bartolotti

Heredity and Environment On your paper, list 10 physical and/or emotional traits that you have. In the columns marked “heredity” and “environment,” place a check mark next to those traits you believe are a result of either your heredity or your environment. Share with your neighbor

Section 4: Heredity What is heredity? Heredity is the transmission of characteristics from parents to offspring. Heredity gives a person their height, hair texture, eye color, etc. Heredity also helps psychologists to explain why people act the way they do based on what personality and temperament traits they get from each of their parents.

Section 4: Heredity What are some of the other traits that heredity influences? Here is a list of other traits that heredity influences: Shyness Leadership Abilities Aggressiveness Interests in arts and crafts Psychological Disorders such as depression, anxiety, schizophrenia, and even alcoholism.

Section 4: Heredity What are genes? Genes are the basic building blocks of heredity. Traits are determined by pairs of genes. Genes are found on chromosomes, and are formed of DNA. We get 23 chromosomes from each of our parents to make 46 total. It is the male that determines the sex chromosome of the child. We each get one x chromosome from our mom, and either an x or a y chromosome from our dad. XX = girl Xy = boy

Truth or Fiction Revisited Truth or Fiction: It is the father who is responsible for the sex of the child? Truth! If you don’t like the fact that you are a boy or a girl, go blame your dad!

Section 4: Heredity What happens when a child is born without 46 chromosomes? Physical and behavioral disorders may be a result. This happens in disorders like Down syndrome, where there is an extra chromosome on the 21 st pair. Although a person with Down Syndrome has some type of mental retardation, children with Down Syndrome enjoy many of the same activities that other children enjoy and they may go on to lead active lives.

The Nature Vs Nurture Debate Nature Refers to what people inherit. Think of this as your genetics – it’s what nature gave you. Supporters of the nature debate argue that a person’s traits and personality are primarily determined by their biological makeup. Nurture Refers to the environmental factors that affect a person. These are the things that a person experiences in their life. Supporters of the nurture debate argue that the environment we live in – not our biological makeup – determine how we think and behave.

So, is it nature or nurture? To believe solely in one view or the other is extreme. Psychologists tend to believe that humans are a combination of both their genetics (nature) and their environment (nurture). For example, someone may have the genetic potential to be a grand concert pianist, but unless they had a piano in the home or were ever exposed to piano lessons, they may not end up becoming that pianist. So, heredity is not necessarily destiny because the environment plays a role in determining who we are.

Kinship Studies The most common way to sort out the roles that heredity and environment play in determining a trait is to do kinship studies. Kinship refers to the degree to which people are related, based on the genes they have in common.

Kinship Studies Identical twins share 100 percent of their genes. A parent and child share 50 percent of their genes, as do full brothers and sisters. Aunts and uncles related by blood share 25 percent of their genes with their nieces and nephews. First cousins share about 12.5 percent of their genes. Psychologists use this information to determine, then, how much personality is shaped by genes or environment.

Twin Studies The study of identical and fraternal twins helps psychologists observe the differences between nature and nurture. Identical twins share the same genetic makeup, so any differences between the two of them must be due to the environment. For example, if one likes rock and roll and the other likes jazz, that is due to the environment instead of their heredity.

Twin Studies Identical twins share traits like shyness, irritability, and even happiness. They also are more likely to share genetic disorders like schizophrenia and autism. Fraternal twins, on the other hand, share only 50 percent of their genetic makeup, so, differences between them could be due to genetics or environment.

Imagine that seeds from the same mixture are sown in normal and deficient soil. Although height differences within each box will be due to genetics, the height difference between groups will be due to the environment, and it will be harder for us to know how much of that height difference was due to genetics, because we will never know what the potential for their height could have been. Copyright © Allyn & Bacon 2007

Adoptee Studies One problem with twin studies is factoring in that identical twins are raised in the same environment so it is tough to determine whether or not their similarities are nature or nurture. One way to study this is by looking at adoption studies of identical twins who have been reared apart. If twins act more like their biological families than their adopted families, then their behavior is largely influenced by heredity. Share video clip of the Jim Twins.

What is the Nature Vs Nurture Debate? How much of our personality and traits are determined by genes and our environment.