2.7 Genes and Behaviour

What are Genes

• They are segments of DNA

• Carry the instructions for the development every cell in the body.

What are Genes made up of?

specific sequences of nucleotides = the building blocks of DNA.

determine the specific traits/characteristics of an organism.

Where are genes contained in the human body?

In chromosomes
Cell with nucleus = chromosomes

What is a chromosome?

thread-like structure that contain a DNA molecule

long DNA molecule is tightly coiled many times around supporting proteins

Package of DNA

What is DNA

Deoxyribonucleic acid = basic unit of inheritance

Set of Genes?

The set of Genes = genotype.

The set of traits manifested = phenotype.

What is a phenotype?

observable traits that result from the interaction of genotype with the environment.

E.g. height, weight, eye colour

Nature vs Nurture

long-lasting debate in psychology

attempts to establish whether human behaviour is determined primarily by biological factors or environmental factors

Methods of research for the nature vs nurture debate?

research design

investigates genetic and environmental factors

compares similarities and differences of relatives with common ancestry.

What do Twin Studies allow researchers to estimate?

proportion of variance in a trait due to genetic and environmental factors (genetic heritability)

Genetic heritability

The quantitative measure of the relative contribution of genetic factors into a trait or behaviour.

How is Genetic heritability estimated?

twin studies

based on the Falconer model.

Falconer Model

assumes phenotype is comprised of three types of influence. There are: genetics, shared environment, individual environment (I = A + C + E)

Kendler et al.

Used the Falconer model to estimate genetic heritability while investigating the environmental and genetic influences on the risk of major depression

Kendler et al. year

2006

Aim 1: Past Studies

Past studies suggest a 35-45% heritability of major depression. Would this be true in a large Swedish sample

Aim 2: Gender

Are there significant gender differences in the heritability of major depression

Aim 3: Factors

Is there evidence that genetic and environmental factors in major depression differ over time

Method

Correlational Studies

Design

Independent Measures Design

Sampling Strategy

Purposive Sampling (Swedish twin registry)
15,493 complete twin pairs

IV

Sex or zygosity

DV

Concordance of diagnosis

Procedure 1

Team of trained interviews - telephone interviews

Maths 1998 - Jan 2003

Procedure 2

Assessment criteria - modified DSM 4

Procedure 3

Also asked questions about the twins ‘shared environment’ and their ‘individual specific environment’

Findings 1

8056 twins met criteria for a diagnosis of major depression at some point in life
322 voluntarily discussed antidepressant treatment

Findings 2: Condordance

Female-Female MZ: 0.44

Female-Female DZ: 0.16

Male-Male MZ: 0.31

Male-Male DZ: 0.11

Male-Female DZ: 0.11

Conclusion 1

Heritability of major depression was significantly higher in women than in men - sex specific
Monozygotic was much higher
0.38 heritability of depression estimated

Conclusion 2

No correlation between number of year lived together and MDD

Conclusion 3

Confirms the level of heritability of MDD found in other studies

What study should be used with Kendler for an ERQ about Genetics and Behaviour

Weismann

Weismann et al. Year

2005

Aim

To study the potential genetic nature of MDD over 3 generations

Method

Correlational, longitudinal

Design

Independent Measures

Sampling Strategy

Purposive; 161 grandchildren and their parents and their grandparents

IV

Whether they were an outpatient (or relative of) or a non-patient local resident

DV

Concordance of diagnosis

Procedure 1:

Study spanned 20 years, tracking families at high/low risk for depression.

Original depressed (now grandparent) sample came from a mood disorder outpatient clinic; controls from the same community.

Parents and children were interviewed four times.

Now adults, the children have their own children, enabling third-generation analysis.

Data was collected by clinicians blind to prior diagnoses and interviews.

Researcher triangulation increased credibility.

Children were assessed by both a child psychiatrist and a psychologist.

Procedure 2:

.

Findings 1:

Inter-rater reliability;

0.82 for MDD

0.65 anxiety disorders

0.94 alcohol dependency

Findings 2:

High rates of psychiatric disorders in the grandchildren with two generations of MDD

12 years old, 59.2% grandchildren already showing signs of psychiatric disorder (most commonly anxiety)

Increased risk of disorder if depression was observed in both grand and parents

Severity of depression correlated with an increased rate of mood disorder in children

Parent depressed by grandparent wasn’t = no significant effect of parental depression on grandchildren