Genetic Influences


Cells - the fundamental working units of every living system

Cell activity directed by DNA

DNA (deoxyribonucleic acid) - complex molecule containing the genetic information making up the chromosomes

Contains instructions for creating a unique living organism

Genome - An organism's complete set of DNA

Vary in size across species

600,000 - 3 billion base pairs

Almost all human cells contain a complete genome

Chromosomes - Molecules composed of coiled chains of DNA

Contain many genes

Are the physical and functional units of heredity

A specific sequence of DNA bases encode intructions about how to synthesize proteins

Human Genome Project

International effort begun in 1990

Finished in 2003

Project goals

Determine complete sequence of DNA subunits (bases)

Identify all human genes

Make results accessible to further study


Human genome

3164.7 million nucleotide bases

Average gene contains 3000 bases

Genes vary widely in number of bases

Approximately 30,000 total genes

Function unknown for over 50% of genes

Share 95% - 98.5% of bases with apes

Degree of similarity varies by ape species


Humans share 99.9% of bases in genome

Interest is in .01% of differences and how it manifests in individual differences

Gene Influences

Relatively few traits influenced by a single gene

Inherit 23 chromosomes from each parent (46 total)

Contain alternate genes for same traits

Dominant genes override recessive genes

Two recessive genes necessary for expression of recessive trait

Eye color example

Hair color example


Dimple example


Gene complexes

Interactions of several genes to determine a trait

Have identified genes with potential for harm

Genetic revolution

Genetic testing

Tests exist for 24 illnesses

Used to predict predisposition to those illnesses

Some are curable

Others aren't

Genetic privacy

Worry that genetic information can be used against a person



Example of violation of genetic privacy

The case against the Burlington Santa Fe Railroad (2001)

Genetic testing lawsuit

Railroad collected genetic samples without permission

Used to evaluate compensation claims

Cambridge Counsel for Responsible Genetics

Documented hundreds of cases of genetic discrimination in the health industry

Laws against genetic discrimination in health insurance

In 40 states

Laws against genetic discrimination in workplace

In 20 states

Genes interact with Environment

Genetic predispositions = increased risk

Environment interacts with predisposition

Interaction determines expression of gene


Affects 1 out of 10 adults

Affects mood, energy, sleep, appetite, interests

Suicide risk

Drug therapy

Selective serotonin reuptake inhibitors (SSRI's)

Depression and the hippocampus

Implicated in memory/concentration problems with depressed patients

Brain imaging

More depression = smaller hippocampus

SSRI protects against shrinkage of hippocampus

Childhood trauma & depression

Trauma is a risk factor for depression

Lowers set point on "stress thermometer"

Results in persistent neurological changes in the brain

New Zealand study

Followed 1000 children for 30 years

Recorded life events

Recorded episodes of depression

Took genetic samples

Focused on serotonin transporter gene

Short or long form

Short genes + childhood trauma = increased risk for depression

Therapy & Depression


Affects primitive brainstem area

Cognitive behavioral therapy

Affects frontal lobes and hippocampus


First cloned animal


Dolly the sheep

Set stage for the possibility of cloning humans

October 2001

First cloned human embryos were created

December 2002

Raelians claimed they had brought first human clone into the world

Now considered to be a hoax

To what degree would clone resemble genetic donor?

Evidence suggests that environment would keep clone from being identical

Includes prenatal environment

Effects of prenatal environment seen in cat clone

CC differs from genetic twin

Coat color & temperament

Cloning procedure

(Just for interest - Do not have to know details for exams)

Other clones

Rainbow - first cloned pet (2001)

Tetra - first cloned monkey (2000)

Cloned cow - first clone of a clone (2000)

Snuppy - first cloned dog (2005)

Noah - first clone of an endangered animal (Bull Gaur) (2000)

National Academy of Sciences

2001 - Decided human cloning should be banned

Serious risks

Poor success rates

Bill making cloning illegal

Passed the US House of Representatives

Failed in the Senate

Behavioral genetics

The study of the relative power and limits of genetic and environmental influences on behavior.

Twin and adoption studies

Determine genetic contribution to behavior

Identical twins

Share entire genetic structure

Fraternal twins

Share half of genetic structure


Share no genetics but similar environments

Identical twins reared together

Identical are more similar than fraternal on many traits

Divorce rates

Fraternal twin divorced

Other twins chance of divorce increases 1.6 times

Identical twin divorced

Other twins chance of divorce increases 5.5 times

Suggests divorce risk is 50% attributable to genetic factors


Identical twins reared apart

Identical genetically but different environments


Show surprisingly high correlations on a number of traits.

Intelligence correlates 60% - 80% (depending on study)

Score similarly on personality traits

Low of 39% for achievement

High of 55% for harm avoidance

Similarities questioned

Similar environments

Separated an average of 5 months after birth

Shared prenatal environment

Placed in similar adoptive homes

Reunited an average of 2 years prior to twin study

Even strangers share many coincidental similarities

Adoption studies

Compare adopted children to biological and adoptive parents

If trait is highly heritable

Will be more similar to biological parent

If trait has high environmental component

Will be more similar to adoptive parents


More affected by heredity than environment

Adopted children more similar to biological parents than adoptive parents

Experience and Brain Development

Experience affects brain development throughout lifetime

Brain maturation and organization

Mental "exercise" affects mental capacity

Environments offering complex experiences

Cell survival increases

Greater number of dendrites

Greater number of connections between dendrites

Enriched vs impoverished environments study

Impoverished environment

Stored singly in bare cages

Enriched environment

Rat colony



Enriched environment stimulated brain growth

Brain weight

Number of synapses

Rats and touch

Infant rats deprived of normal maternal contact

Did not gain weight

Developed poorly

Traced to increase in beta-endorphin production

Mimic touch (with paintbrush)

Decreased beta-endorphin production

Increased protein production

Pre-term infants and touch

Increase in weight gain

Increased alertness

Earlier discharge from hospital

Used cautiously with high-risk pre-term babies

Deprivation or stressful experiences

Limit brain development

Exploring means for reversing damage

Placing in stimulating environment helped regain some function

Humans are born with an overabundance of neurons

Environment determines connections

Develop or prune

Early years are critical

Overabundance of neurons makes learning some things easier

Without use, pruning will eliminate "extra" neurons by puberty

Brain continues to develop throughout life

Neural tissues change to reflect experience

Use = strengthening pathways and connections

No use = weakening pathways and connections