GENES AND EXPERIENCE:Hybrid vigor, Chromosomal Abnormalities

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Neurological Basis of Behavior (PSY - 610)

Lesson 11

GENES AND EXPERIENCE

Objective:

· To understand the Brain behaviour relationships from the perspectives of biological systems.

In this section of the module the students would go through and understand Biological systems- their

genetic basis and similarities with other animals. Mendelian Genetics. Where is the genetic

programming of behaviour (if any) Watson Crick Model. What are the similarities and differences

between species, progenies of higher order animals, including homosapien? How much do genes

contribute to behaviour: The discipline of Behavior genetics

In breeding

Children of very close genetic relationships (incestuous), were studied by Adams and Neal (1967).

There were 18 unrelated, 18 such cases in their study. They reported that in these cases 5 died and 2

mentally retarded and there were other problems and only 7/18 were normal (physically and otherwise).

As compared to this group there was problem in only one case in normal and there were 17/18 normal

(any physical or other defect). Thus, restricting the gene pool further leads to serious aftereffects.

Sociobiology of incest: why forbidden in all religions?

Barash (1977), states "close breeding reduces the fitness of the participants because of the reduced

viability of the offspring produced. Incest taboo has genetic predispositions."

Natural selection pressures work on the gene pools, if reduce gene pools; reduce genes available bad

genes show up.

Hybrid vigor: if two different gene pools are mated their offspring is stronger and there are greater

chances of survival in animals (horses, dogs, cows,) birds or vegetables, flowers or people of Asia!

Behavioural Defects Due To Genes

The following behaviours and genes have shown to be linked

Deficiencies Due To Single Gene Defects

In some cases defect in one gene at one locus affects total behaviour. Some of these are discussed in

details as follows:

Phenylketonuria (PKU): This is characterized by mental retardation and queer

smelling urine, which is identified as the presence of phenyl pyruvic acid in urine. This is an

amino acid disorder. Asbjorn Folling (1934) Austrian dentist first noticed it in two of his

children with symptoms of vomiting, irritability, seizures and hyperactivity. This is due to

inheritance of a double recessive gene for this disorder as parents are homozygous. This

disorder completely upsets the biochemical pathway creating toxins which damages the brain

irreversibly. There is Irreversible brain damage due to buildup of phenylpyruvic acid and

byproducts--toxin what can be done? Hospital checks immediately after birth if results are

positive then these babies are place on a controlled diet to reduce the damage. However, the

timing of treatment is important especially when the brain is developing rapidly. Diamond

and colleagues (1997) have shown that early control reduces but not completely eliminate

cognitive deficits which are similar to prefrontal damage.

Neurological Basis of Behavior (PSY - 610)

Tay-Sach's disease: Infantile and juvenile cerebral lipdosis or amauratic idiocy. This is

a defect in the lipid metabolism due to a double recessive gene at single locus which means

that both parents are carriers. This is found mainly in Eastern European Ashkenazi Jewish

families. Homozygous for this gene do not survive.

Infantile form of this disease is found mainly at a few months of age (during 1st year);

the symptoms are motor weakness, blindness (cherry red spot in the retina) and mental

deterioration. Death occurs in 1-3 years.

Juvenile form is found at around 2-10 years of age with similar symptoms i.e. optic

atrophy, blindness, paralysis, mental deterioration eventually death.

Huntington's chorea: is characterized by a progressive degeneration both physical and

mental. This is due to a dominant gene which is transmitted to males only. In this disorder the

cortex and Basal ganglia are affected. Damage to the Cortex results in dementia (forgetting)

and damage to the, Basal Ganglia leads to involuntary jerky movements. Drugs are given to

control movements. The onset of this symptom is between 30-50 years, death occurs between

5-20 years with rapid progression of deterioration.

Alzheimer's genetic transmission is shown to occur especially in cases where it shows

up in young. Chances increase if a close relative has it. The case of Hannah's heirs- Jewish

mother from Russia had it and 5/8 children developed Alzheimer's during their late 40's

Chromosomal Abnormalities

The abnormalities which occur to the defect in the chromosome and follow the transmission of the

chromosome are several. These are discussed as follows:

1. Downs Syndrome (mongolism). In a normal human there are 23 pairs of chromosome

(23from other and 23 from father) which is then 46 chromosomes. However, in some cases

there is an additional chromosome which adds up the total to 47 chromosomes. There is a

trisomy (instead of two there are three chromosomes) at pair number 21. This can occur

sometimes at pair number 15, (or pair number 21 intermingled with #15- during sex cell

formation and the #15 carries an extra #21). The older the age of the mother, the more

chances of downs syndrome in the child. Therefore now amniocentesis is routinely required to

test for this to prepare parents and to advise them.

2. Klienfelters Syndrome (XXY), this is a genetic anomaly related to the sex chromosome. One

extra X is transmitted to an otherwise normal male pattern-male with female characteristics or

a masculinized female. There is atrophy of reproductive ducts, sometimes mental retardation

and some personality problems (not in all cases)

3. Turner's syndrome: this involves a missing sex chromosome. There is only one X

chromosome. These are females, short stature, with ovaries not developed. They have normal

intelligence however are deficient in spatial discrimination (spatial discrimination space-form

blindness- cant copy figures right.- hypothesis that this trait may be sex linked?)

4. XYY Syndrome: this is also a chromosomal anomaly where an additional Y chromosome is

attached to the normal male pair. These males are taller, muscular, and sturdy slightly

retarded. The extra Y increases in maleness and aggression. Research on jail inmates with

aggressive, brutal crimes (Jarvick, 1973) Incidence 2-13% in Jail pop whereas in normal it is

about 1%.

5. Lesch-Nyhan syndrome: this is due to a recessive gene carried on the X chromosome found

only in males. The symptoms are Cerebral palsy, involuntary movements of the limbs, hands,

Neurological Basis of Behavior (PSY - 610)

feet and facial muscles, self mutilation lips mouth and fingers. This is due to an enzyme

deficiency with an extreme over production of uric acid. Self mutilation is due to increased

Dopamine B-hydroxylase in plasma.

Behavioural Characteristics

Studies have used the monozygotic (same egg, same sperm, same time fertilization)) or dizygotic

twins (different eggs, different sperms, same time of fertilization) to identify behavioral defects due to

gene defects. Genetic influences on Human behaviour utilizes twin studies paradigm:

The MZ twins have 100% genes common, and the DZ are like other siblings with 50% genes in

common

Monozygotic and dizygotic twin studies follow many different methodologies from comparing those

who have been reared together in the same environment to those reared apart in different environment

(adoption /foster parents)

In adoption studies if behaviour is similar to that of the biological parents then behaviour is due to

genes, however, if their behaviour was similar to their adopted parents then the behaviour can be

attributed to the effects of environment. Comparisons of performances of related and unrelated

individuals are made on a wide range of tests. It is the behavior geneticist who would be able to

estimate how much is due to gene (variation: genetic), and due to environment (variation:

environment)

In studying genetic basis of behavioral ( especially complex behaviours), it must be remembered that

a) more than one characteristic make up a trait and b) these traits are continuous i.e. in gradations of

more/less such as I.Q., Schizophrenia, alcoholism. Therefore, the task of the behavioral geneticist is

not an easy one; however, there have been studies which have identified genetically transmitted

mental illness as well other disorders.

Schizophrenia

Twin Studies: This is a genetically inherited disorder as evidence by multiple research studies has

supported this. The incidence of schizophrenia in general population is 1% .This rises if there is a close

relative with schizophrenia ie. With siblings and dizygotic twins this rises to 10-15%, and the

expectancy of schizophrenia if one parent has it is about the same i.e.-10-15%. However, if both parents

have it then the expectancy rises to 40-65%. Schizophrenia is due to chemical, neural and biological

imbalances created by genetic codes. These imbalances in could be due to inheritance of a) recessive

gene from both parents or b) a dominant gene from one parent who has this disorder. Evidence from

genetic predisposition twin studies a review of 17 studies from 1928 to 1972 from all over the world

showed that the highest incidence is among MZ twins and lower among DZ.

Rosenthal's (1959) study on MZ twins with schizophrenia reports 60% presence in concordant twins,

males had a later age of onset and a more favorable outcome. Inouye (1961) reported studies carried out

in Japan and identified 3 groups of monozygotic twins. There was chronic schizophrenia (17/23: 74%

concordant). Mild transient 9/23 (39% concordant).

Foster child studies: excellent, now classic study by Heston (1966) followed 50 children born to

schizophrenic mothers and separated within a few days after birth. For controls he took 50 children born

to normal mothers. There was a higher Incidence of schizophrenia/personality disorder and other

abnormalities in 47/50 children of schizophrenic mothers. There were 5 schizophrenics, 4 were mentally

retarded, 9 were antisocial, and 13 had neurotic personalities. In controls there were only 2 with

personality and 7 with neurotic personalities.

Neurological Basis of Behavior (PSY - 610)

Thus there is strong evidence to link schizophrenia with genes transmitted to the offspring. Research in

the more recent years has also shown the same (see Pinel page 463-464).

References:

1. Kalat J.W (1998) Biological Psychology Brooks/ Cole Publishing

2. Carlson N.R. (2005) Foundations of Physiological Psychology Allyn and Bacon, Boston

3. Pinel, John P.J. (2003) Biopsychology (5th edition) Allyn and Bacon Singapore

4 Bloom F, Nelson and Lazerson (2001), Behavioral Neuroscience: Brain, Mind and Behaviors (3rd

edition) Worth Publishers New York

6. Bridgeman, B (1988) The Biology of Behaviour and Mind. John Wiley and Sons New York

7. Brown, T.S. and Wallace, P.M. (1980) Physiological Psychology Academic Press New York

Note: References #2, 3,and 4 are followed most closely, as they have been used in teaching as well,

further individual references/pages are also given on the power points of each lesson

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