Genetics and Behavior

With reference to relevant research studies, to what extent does genetic inheritance influence behavior?

Like many other animals humans have sex

• Conception begins with the drop of an egg and the release of about 200 million sperm.

• The sperm seeks out the egg and attempts to penetrate the eggs surface.

Once the sperm penetrates the egg- we have a fertilized egg called……..

• A zygote

Zygote• Less than half of all

zygotes survive first two weeks.

• About 10 days after conception, the zygote will attach itself to the uterine wall.

• The outer part of the zygote becomes the placenta (which filters nutrients).

After two weeks the zygote becomes a…

Embryo• Lasts about 6 weeks.• Heart begins to beat and

the organs begin to develop.

By nine weeks we have a…Fetus• By about the 6th month, the

stomach and other organs have formed enough to survive outside of mother.

Then we have childbirth….

But why go through all that trouble?

Wouldn’t it be easier if people could just copy themselves instead of going through all these messy stages?

• Watson and Crick in 1953 discovered the DNA molecule.

• SEX and the birthing process brings together the genetic information from to parents in a fertilized egg.

• GENETIC DIVERSITY

Chromosome Breakdown

Chromosomes DNA

Genes Nucleotides

Genetic SimilaritiesMr. D is

98% 99.9%

99.9%

Gene Mapping

• Some scientists are trying to determine the effect of a particular gene on behavior such as temperaments or psychological disorders.

Caspi et al. (2003)The role of the 5-TT gene in depression after stressful events.

• Longitudinal Study (vs Cross Sectional)

• The 5-TT gene influences the level of serotonin, which is known to play a role in mood.

Caspi et al. (2003)The role of the 5-TT gene in depression after stressful events.

• There are two types of 5-HTT genes.

• Long- a little over 50% of population

• Short- a little less than 50%• The researchers compared

participants with normal 5-HTT (long) genes with shorter alleles.

• Specifically after stressful events.

Caspi et al. (2003)The role of the 5-TT gene in depression after stressful events.

Results• After stressful events,

the participants with the shorter 5-TT gene were more likely to become depressed.

• The 5-TT gene could indicate vulnerability to depression.

Caspi et al. (2003)The role of the 5-TT gene in depression after stressful events.

Evaluation• Since so many people carry it

(almost half the population), it is hard to say that in is the gene that made the difference.

• Maybe it was the environmental factors (stressful events) that caused the depression.

• Did not show a cause-effect relationship.

Chromosomal Abnormalities• Gender comes from

23rd pair of chromosomes…men have XY…woman have XX.

• Turner’s syndrome is single X.

• Klinefelter’s syndrome is extra X…XXY

• XYY- Super male