1. Heredity: Our Genetic Background
Psychology: Chapter 3, Section 4

2. Heredity: Our Genetic Background
Heredity is the transmission of characteristics from parents to offspring
The traits we inherit help shape our behavior
Shyness, leadership ability, aggressiveness, even an interest in arts and crafts are influenced by heredity (while environment also plays a big role)
Psychological disorders, such as depression, schizophrenia, bipolar disorder and alcoholism are also affected by heredity

3. This chart seems to indicate that the closer someone is related to someone with schizophrenia, the more likely that person is to develop a similar diagnosis

4. Genes and Chromosomes Genes are the basic building blocks of heredity
Genes match up in pairs, one gene in each pair from each parent. As these genes pair up, traits are determined.

5. Genes and Chromosomes
Genes are found in threadlike structures called chromosomes
Chromosomes are composed of deoxyribonucleic acid (DNA)
DNA looks like a twisting rope ladder (called a double helix)

6. Genes are the building blocks of chromosomes

7. DNA: The Genetic Code
The threadlike molecules of DNA that make up chromosomes contain the codes for the development of particular traits.
Each chromosome has more than 1000 genes.
The rungs in the ladder form the genetic code that causes the organism to develop certain traits, and can be the source of some mutations

8. Genes and Chromosomes
Most normal human cells have 46 chromosomes, organized into 23 pairs
In each of the 23 pairs, one chromosome comes from the father and one from the mother
These chromosomes contain instructions for traits.
That mixing of chromosomes is why you may look and act a little like your mother and also like your father

9. Genes and Chromosomes
22 out of 23 of the chromosomes are the same for both males and females
The 23rd pair is the sex chromosome, determining whether we are to be male or female
In females, both chromosomes are in the shape of an X, so they are both called X chromosomes (XX)
In males, one of the chromosomes looks like a Y, so the males are said to have XY
This X or Y is contributed by the father; he determines the sex of the child

10. In the case of these 23 chromosome pairs, this offspring is a boy, as he has the larger x chromosome matched with the smaller y chromosome in the 23rd pair

11. Genes and Chromosomes
Occasionally, there is a mutation where there are not 46 chromosomes in each cell
If there is an extra chromosome on the 21st pair, then the baby will be born with Down syndrome.
Down syndrome usually means there will be some level of mental retardation, with some heart and respiratory problems

12. People with Down syndrome have some similar facial features

13. The Nature- Nurture Debate
For many years, people have debated about the role of biology in determining who we are as people
This is often called the Nature-Nurture debate
Nature refers to what people inherit biologically from their parents
Nurture refers to how a person is raised– living conditions, parental involvement, educational opportunities, etc.

14. The Nature- Nurture Debate
Most psychologists agree that influences from both nature and nurture determine our psychological traits
There may be someone who has the genetic potential to write a brilliant novel, but won’t because she never gets the chance to read or write
Heredity is not destiny, but it is a predisposition within an environment

15. Nature vs. Nurture
We inherit our physical, intellectual, and emotional characteristics from our ancestors, but these things are also greatly affected by where/ how we live.

16. Kinship Studies
The most common way to figure out the roles of heredity and environment is to do kinship studies
Kinship is based on degree people are related
Identical twins share 100% of their genes
A parent and child shares 50% of their genes (1/2)
Brothers and sisters also share 50% (1/2)
Aunts/ uncles share 25% with their nieces and nephews (1/4)
First cousins share 12.5% (1/8)

17. Kinship Studies
Psychologists can look at traits in individuals and see how they compare with relatives
Two common types of kinship studies are twin studies and adoptee studies

18. Identical twins share 100% of their genetic code, whereas fraternal twins are basically just like any other siblings

19. Twin Studies
Studying identical and fraternal twins can show a lot about nature vs. nurture, as identical twins share 100% of the same genetic makeup
If identical twins are more similar on a certain trait than fraternal twins, then that could be an indication that that trait is influenced by genetics

20. Twin Studies
Some traits that do seem to be more similar between identical than fraternal twins are shyness, activity level, irritability, sociability, and overall happiness
Autism is highly linked by genetics– if one identical twin has autism, there is a 96% chance the other has autism. In fraternal twins, there is a 24% chance.

21. Adoptee Studies
One problem with twin studies is that identical twins tend to also be raised in the same environment and treated similarly, so that complicates the nature/ nurture discussion
But if twins were adopted, then they would have different environments but still the same genetics

22. Twins Reared Apart
It can therefore be useful to study twins who were raised apart from each other
In such studies, researchers have found that intelligence, following rules, risk avoidance, aggression, and leadership traits were very similar in twins, even when reared apart
They also may sit or stand very similarly, and have similar tastes in clothing
Twins: Is it All in the Genes?

23. Assessment
Complete the three questions on page 72