Development and Behavioral Genetics

PSC 113Jeff Schank

Outline

• Unifactorial Methods– Vasopressin Deficiency

• Multi factorial Methods (Quantitative Genetics)– Heritability– The IQ Controversy– What are Intelligent Tests?– Are Intelligence Tests Valid?– Is IQ heritable?

Unifactorial Methods

• Unifactorial genetic analyses focus on single gene effects whereas multi factorial (Quantitative Genetic) approaches focus on multiple gene effects

• Unifactorial methods typically use inbred strains of animals with a singe-gene mutation and compare them to out bred strains

• Problems– Not all aspects of an organism’s environment are easily

controlled, e.g., intrauterine, birth, and maternal effects– Genes can have pleiotropic effects, which means that one

gene may affect multiple, often unrelated, phenotypic traits

A Single Gene Effect: PKU (Phenylketonuria)

• Is a condition that leads to severe intellectual impairment of human functioning

• The condition occurs when there is a single recessive gene present in both sister chromosomes that play a role in the liver’s production of the enzyme phenylalanine hydroxylase

• Without this enzyme, the amino acid phenylalanine is not converted to tyrosine

• The consequence of building up phenylalanine is structural malformations of the brain, resulting in children that are mentally retarded and irritable

• However, by modifying diet, to greatly lower the intake of phenylalanine, this condition can be largely avoided– Molly's Story

Transgenic Organisms

• A knockout organism is created by disabling a specific gene

• A Knockin organism is created by inserting a specific gene into the genome

Part IPart II

Issues with Transgenic Organisms

• Typically produced in inbred animals• As we would predict, genes expressed earlier in development,

when knocked out (in), are often lethal• Knocking out (in) a gene is somewhat analogous to making a

part of a machine non-functional – It is relatively easy to see how the machine breaks down, but not as

easy to identify the functional role in a complex regulatory system.• This type of genetic engineering has often been more focused

on creating organisms that have some technological use such as – Roundup ready plants– Human insulin– GMO Corn

A Natural Knockout: Vasopressin Deficiency in the Brattleboro Rat

• The Brattleboro, di/di, rat strain was discovered in the laboratory of Henry A. Schroeder in Brattleboro, VT, USA in 1964 (Valtin Ann New York Acad Sci, 1982; 394: 1-9)

• It turned out to be a single base deletion at nucleotide 1552 in a conserved region of exon B resulting in a frame shift mutation that produces analtered amino acid sequence (Schmale , Richter Nature, 1984; 308: 705-709)

• Immunohistochemical and in situ hybridization studies showed that the vasopressin gene is transcribed and translated in di/di rats, but with an impaired response to physiological stimulation (McCabe, Morrell, Ivell, Schmale, Richter, Pfafp Neuroendocrinology, 1986; 44:361-364)

Brattleboro Rat continued

• Brattleboro rats develop diabetes insipidus at least by the time of weaning with indications of AVP deficiency even earlier in development (Dlouha, Nrecek, Sicha Annuls of the New York Academy of Science, 1982; 394: 10-20)

• AVP deficiency also affects social behavior by modulating – aggression – pair bonding – social recognition (Caldwell, Lee, Macbeth, Young Prog Neurobiol, 2008; 84:1-24)

Autism Spectrum Disorder (ASD)

• What Is Autism Spectrum Disorder?• Animal model Issues– No communication analog– Difficult to compare social deficits– Difficult to compare patterns of behavior

• Possible bases for comparison– General social deficits– Behavior: stereotypical behavior, hyper activity,

sleep problems

ASD, Animal Models, and Vassopressin

• ASD may be associated with vasopressin resistance due to hyporesponsiveness of AVP V1a receptors (Boso, et al, 2007)

• Knockout mice lacking V1a receptors have deficits in social recognition resembling aspects of ASD (Bielsky, Hu, Ren, Terwilliger, Young Neuron, 2005; 47:503-513)

• Brattleboro rats exhibit social deficits in recognition (Engelmann, Landgraf Physiol Behav, 1994;55:145-9)

• Brattleboro rats exhibit abnormalities in emotional reactivity (Williams, Carey, Miller 1985; 6(Suppl. 1): 69-76)

Is AVP Deficiency Detectable in Rat Pups?

• Fifteen-day-old di /di pups exhibit reduced social attachment as measured by odor preference and approach latency learning (Nelson, Panksepp. Neuroscience & Biobehavioral Reviews, 1998; 22: 437-452)

• By day 10, di/di pups have an impaired adrenocorticotropin stress response to separation from their mother (Zelena D et al Endocrinology, 2008)

• These results indicate that AVP deficiency is behaviorally detectable early in life and they are related to abnormalities detected in adult di/di rats

Development in Rat Pups

Figure 1. Locomotor neural development in rats has four stages. During the fetal stage, motor neurons become excitable, the CPG begins to function, and the first projections from the brainstem develop. During the immature stage, infant rats crawl, maturation ofposture in locomotion proceeds cephalocaudally, the cotricospinal tract begins to develop around day 7 after birth, and by day 10 (the end of the immature stage) coupled activity in groups can be detected. During the transitory period, the eyes and ears open and walking begins. By the beginning of the adult period, adult locomotion begins.

Social Behavior of Brattleboro Rats in a Temperature Controlled Arena

Measuring Behavior: Metrics• Activity: change in position or orientation between each time interval;• Distance: if active, the distance moved over a time interval as measured from the tip-of-

the snout• Orientation: if active, the change in body orientation over a time interval as measured in

degrees• Wall contact: body contact with a wall of the arena at each time interval• Corners: the number of corners visited by a pup during an experimental session• Inner cells: the arena was divided into an array of 6 X 9 cells of equal size with inner cells

defined as the number of cells not adjacent to a wall that the tip-of-the-snout entered• Outer cells: the total number of cells adjacent to a wall that the tip-of-the-snout entered• Total cells: the proportion of the total number of cells that the tip-of-the-snout entered.

For group trials, there was one additional metric• Subgroups: the number of different contact groups that formed out of eight pups at each

time interval, which ranged from 8 (no pups in contact with each other) to 1 (all pups in direct or indirect contact)

Were there Effects?

Effects of Sex?

7-Day Old Pups

10-Day Old Pups

Individual Metrics

Individual Movement

Figure 3. Trajectory plots of 145 tip-of-snout points for a 12-minute session. The two plots on the left are from two di/di, 10-day-old pups that visited four corners. The two on the right are typical one-corner visits by +/+ (top right) and +/di pups (bottom right).

Group Metrics

Activity/Inactivity+/+ +/di di/di

Possible Interpretations• A particularly robust and strong result was the distance moved by 10-day old

di/di pups in both individual and group trials• Ten-day-old di/di pups moved over twice the distance moved by either +/+ or

+/di pups in group trials• For individual trials, they visited more corners, entered more cells—especially

those cells along walls• Pups often repeatedly circled the arena, a behavior rarely observed in either

+/+ and +/di pups.• Informal observations of 10-day-old di/di pups revealed that they were often

able to lift their bodies off the surface of the arena and walk or run across the surface.

• Walking or running on the surface of the arena was never observed for either day-10 +/+ or +/di pups

• Another interesting behavior observed in 10-day-old di/di pups was a large degree of turning

Conclusions

• Accelerated motor development also seen in ASD

• High degree of change in orientation a stereotypic behavior?

• Increase activity with contact indicates social deficits

• Lower aggregation indicates social deficits• Failure of activity to decrease over time may be

related to sleep disturbances

Problems

• There were no sex differences. Autism, however, occurs in males in about a 4:1 ratio. – If Vasopressin is involved in autism, it is far from the whole

story– Genetically, untangling the mechanisms of autism likely will

involve understanding some rather complex genetic networks

• Autism is not associated with diabetes insipidus, but if vasopressin is somehow involved, it may be at the receptor level and/or at the gene regulatory level

• How do we know we have an animal model of autism?

Multifactorial Methods (Quantitative Genetics)

• Heritability is based on the statistical idea of variance

• Recall that for natural selection to operate in a population, there must be variation in phenotypes

• If we can measure phenotypes (e.g., the height of corn plants), then we can measure variation using the statistical concept of variance

Phenotypic Variance

• Phenotypic variance can be partitioned into components

• The main empirical problem is how to estimate each component

• The simplest partition is

• where VG is variation due to genetic factors and VE is variation due to environmental factors

Heritability

• Heritability in the broad sense used in the IQ controversy is:

• If components of variance can be estimated for a population, then h2 heritability can be used to predict characters in the next generation.

• If E(x) is the mean measure of the character for a population and xMP = (xi + xj)/2 is the mid parent value, then the offspring of these parents would be expected to have a mean value of

Heritability Example

What are Intelligent Tests?

• The first scale for measuring intelligence was introduced by Binet in Paris for the purpose of testing children in school

• His test was based on the concept of mental age introduce by SE Chaillé in 1887

• The basic idea was to first find the average age at which most children could solve a problem, then second if say a 3 year old could solve problems solved by most 4 year olds, then his/her mental age would be 4 and his/her chronological age would be 3:

• Where MA is mental age and CA is chronological age

Tacit Assumptions of IQ Tests

• Intelligence can be measured by problems that do not take too long to solve.

• Intelligence is “black or white” – There are not different perspectives one can take to a

problem – Are real world problems “black and white”?

• Problem solving can be separated from knowledge – This is assumption is important for those looking for race or

group differences– If problem solving is not separable from knowledge, then

one must show no knowledge differences between groups

IQ Distribution

IQ Test Items

Are Intelligence Tests Valid?

• The validity of a test refers to whether the test really measures what it is intended to measure

• Binet’s aim was to compare the development of intelligence in children

• This is very different from an absolute measure of intelligence in adults

• IQ (and IQ equivalent tests) are only mediocre at predicting– Job performance (at best about 50% of the variance)– First year performance at university or college (about 30% of

the variance)

Is IQ Heritable?

• Some people such as J. Philippe Rushton claims that there are heritable differences in IQ among groups or races of people

• In this video, he presents his statistical arguments

• If one doesn’t have a basic understanding statistics and quantitative genetics, it is difficult to identify the nonsensical use of statistics to support his agenda

Why Can’t Heritability be Compared Between Populations?

• Recall that the basic equation for partitioning phenotypic variance is

• The VE term for IQ tests will vary between groups if there are differences in background knowledge

Heritability and Corn: Two Examples

• Consider two completely inbred lines of corn (one tall strain and one short strain)

• There is no genetic variation within lines because corn plants within lines are identical

• Now if we plant them in different pots (one seed to a pot with ordinary potting soil) and a few weeks after they germinate, we will find variation in the height of the plants

• The variation will be entirely environmental, thus

VP = 0 + VE

h2 = VG/VP = 0

• But, there will be genetic differences between the two lines

• Trying to estimate heritability across to populations is statistically meaningless in this case

Second Example• Now, suppose we take seeds from a sack containing seed of an open pollinated

variety containing lots of genetic variation • We grow each group of seeds in vermiculite watered with a nutrient called Knop’s

solution, which is used by plant physiologists for controlled growth experiments• Suppose however that for one group we twice as much Knop’s solution as the

other • The results we get would be this:

– Within Knops solution conditions, VE would be very close to 0 and thus h2 = VG/VP = 1 within groups

– Between groups there would be systematic differences in height, but it would be entirely environmental

• Thus, again to say that corn height is heritable across groups is statistically meaningless

• This is exactly analogous to the problem of different background knowledge across groups or populations