PSYC 3102: Introduction to Behavioral Genetics
Lecture 12
Remember test on next Tuesday
Covering where we left off at Mendelian Disorders to the beginning of Evolutionary Psychology
Linkage Continued….
Purpose

To find the approximate location of a gene for a certain trait (usually a disease or disorder)

Need long term perspective- it doesn’t find gene, but gets you close (Genome is VERY big)
Definition

Linkage analysis consists of tracing the co-segregation of 1 or more marker genes with a trait gene (for trait or disorder) within pedigrees

Co-segregation – disease and marker genes that co-segregate in families enable the marker gene to be used as a predictor of who will get the disease, and who won’t
Goal

Find gene
 Find protein product

Try to fix things up

Example 1:
Father:
A
D a d
D = dominant disorder gene A = marker gene
Pedigree:
Aa aa
Mother: a d a d
= demonstrates disorder
Aa aa Aa Aa aa Aa aa
Offspring will get A & D or a & d from the father if the loci are close enough to co-segregate
(will get a & d from mother)
This pedigree is consistent with linkage

Example 1:
Father:
A
D a d
D = dominant disorder gene A = marker gene
Pedigree:
Mother: a d a d
= demonstrates disorder
Aa aa Aa Aa aa Aa aa
If marker and trait gene are far away from one another, independent assortment occurs
This pedigree demonstrates a random association with the A allele and the disorder, which indicates that A and D are not linked

Finding genes

Dumb luck: one born with section missing, find out which proteins/enzymes are missing

Somatic cell hybridization: fuse human and mouse cells, make cell lines that contain only one human chromosome and check which enzymes are missing

Polymorphisms: through RFLPs, etc.; can find spelling variations
How do you know the marker gene isn’t the one causing the gene?

Marker genes are usually in non-coding regions, they don’t cause the disease
Back to Linkage…

Linkage gets you into the right ballpark, but not in the right seat

Sections between marker genes and trait genes are HUGE

Techniques are used after linkage analysis to do fine-grain searching

Linkage analysis is super high tech now
 Complicated computer algorhythms are used, no one just ‘looks’ at a pedigree
Linkage and QTL
Linkage analyses can also be done on what is known as a QTL (quantitative trait loci)

QTLs contribute to a continuous trait (like blood pressure, every one has it, but can be between high and low)

If a QTL is linked to locus A, then sibs who share the locus A marker should be more similar than sibs who do not share the locus A marker

This kind of research is widely used in psych (IQ, personality traits, anti-social behavior)


Linkage analyses are very successful in Mendelian disorders, some limited success in diseases with complicated genetics, but mixed progress on most psychopathology
(schizophrenia, etc.)

Because of these limitations of linkage analysis, many people are moving away and going toward more association designs, which only work if you already have a good candidate gene
(but be wary of false positives)
Evolutionary Psychology

Has always been around, but not always called this

People have always been comparing human behavior with that of other species and in terms of evolution

Darwin wrote a book on facial expressions of humans and animals
 Wilson wrote a book dealing with “sociobiology”

The field of Evolutionary Psychology is not new, but has become more developed
Definition
 Examining human behaviors as adaptations to the environment

Human behavior has been subjected to all forces of evolution that the behavior of other organisms has been
Only the eyes are different, but discern one as sad, the other as angry
Only the mouth is different, but discern happy and surprised


How do we recognize these expressions? o We have learned it o It is a built in mechanism
Herring Gull example:
 Offspring pecks at red dot on parent’s beak
 Parents are then prompted to regurgitate food into the offspring’s mouth

Thought to be a built in mechanism; stimulus-response of offspring and parent
Humans and facial expression

Built in?

Learning?

Both?

How to study theories? o Cross cultural studies o Study blind people and infants
Cross cultural:
 Show pictures of faces, get same responses (happy, sad, etc.)

Mirrored camera study – unobtrusive pictures of people in different situations, see similar expressions, even in flirting behavior
Blind infants:

Crying babies make same expressions
 However, there is awkwardness noted when older in smiling, implies some learning, perfecting of smiles

If innate, WHY?

Not uniquely human or primate

What is so critical that this mechanism was created and maintained? o COMMUNICATION o Survival (alarm), dominance/submissiveness, societal animals

Test theories: example – are expressions more salient and varied in social animals than solitary animals?
One of the biggest problems is related to the extent that the person promoting an idea / theory really understands evolution, this deals with an incredible amount of complications, nothing is simple.