Determinants of Human Behavior

Heredity and Environment

Berger: The Developing Person Through Childhood and Adolescence, 7th Edition, Chapter 3

The Genetic Code

Chromosomes: a molecule of DNA (Deoxyribonucletic Acid) that contains the instructions to make proteins

The instructions are organized into genes, the basic unit for transmitting heredity.

Humans have 46 chromosomes (23 pairs), and about 25,000 genes.


Karyotype (Map of Chromosomes)


The Genetic Code (cont.)

Human genome: the code for making a human being

Every person has a slightly different code, but the human genome is 99.5% the same for any 2 people.


The Beginnings of Life

Development begins at conception, when the sperm penetrates the ovum.

The organism is first called a zygote, and is the fused nuclei of sperm and egg.

The genotype of the zygote is the genetic information on the 23 chromosome pairs.


Gene Pairs

Gene pairs are closely matched on 22 of the 23 chromosomes.

In some cases, One of two or more alternative forms of a gene that arise by mutation and are found at the same place on a chromosome occurs- (allele ) an alternate version of variable genes.

On the 23rd pair, XX = female, XY = male.


Determining a Zygote’s Sex


From One Cell to Many

The phenotype is the actual appearance and behavior of a person, and occurs because some instructions on the genotype are ignored, and others amplified.

This occurs through cell differentiation, gene-gene (polygenic), and gene-environment interactions.

Examples of genotype:

The gene responsible for eye color The gene responsible for hair color The gene responsible for height The gene responsible for how your voice

sounds


Examples of phenotype

Eye color (brown, black) Height (tall, short) Hair color ( brown, black, brunette)


Heredity

The process and the result of the process by which the characteristics or traits are produced and transmitted from parents to offspring through the genes



Additive Heredity

Additive genes combine to make a phenotype.

Example: HEIGHT. The inherited genes from mother and from father are added together. However, some additive genes get enhanced by other genes, making their input greater.


Dominant-Recessive Heredity A dominant-recessive pattern occurs

when the influence of one gene in the allele is greater than the other gene.

Example: Blood types A and B and brown eyes result from dominant genes.

This pattern may be X-linked (on the X chromosome), in which case males are more affected (e.g., color-blindness).


Twins and Clones

Dizygotic (fraternal) twins result from two sperm penetrating two ova, and share 50% of their genes.

Monozygotic (identical) twins originate from one zygote, and share 100% genes.

A clone originates from a live organism.


Dizygotic or monozygotic?

DAVID YOUNG-WOLFF / PHOTOEDIT BRUCE ROBERTS / PHOTO RESEARCHERS, INC.


Multiple Births

The likelihood of multiple births vary by age and ethnicity. Fertility treatments may also cause them.

Hazards of multiples include birth complications, death, disease, and disabilities.


Research on the Effects of Genes

Researchers have employed several methods (e.g., twin studies, adoption studies) to investigate the relative influence and interaction of genes and environment in shaping human behavior and traits.

The results may surprise you!


Findings from Genetic Research

Genes affect every aspect of human behavior.

The non-shared environment of families is powerful.

Genes elicit responses from other people that shape development (an indirect effect).


Psychopathology Genes have been found to influence

several disorders, including:

SchizophreniaAddictionNearsightedness Diabetes

However, the environment ALSO plays a key role in these disorders.


Chromosomal Abnormalities

Chromosomal abnormalities when the zygote’s cells have fewer or more chromosomes than 46.

Maternal age is the most common correlate of chromosomal abnormalities.

Many zygotes with chromosomal abnormalities are spontaneously aborted.


Down Syndrome (Trisomy 21)

Down syndrome occurs when a zygote has 3 copies of chromosome 21.

Sufferers experience mental slowness, faster aging, and physical problems.

Social support and a positive attitude help.


Abnormalities of the 23rd pair

About 1 in 500 infants have either one too many or too few chromosomes on the 23rd pair.

This can lead to underdeveloped sexual organs (girls), breast development (boys), or other anomalies.


Dominant Disorders

Huntington’s disease is a fatal CNS disorder caused by a genetic miscode. It is inactive until middle adulthood.

Tourette syndrome, a dominant disorder, can lead to uncontrollable tics and obscenities.


Fragile X Syndrome

Fragile X syndrome is caused by a single gene that has 200 repetitions of a triplet.

The effects of Fragile X include cognitive deficits and poor social skills.

Males are at greater risk of developing this syndrome.


Genetic Counseling Genetic counseling provides facts. It is

recommended for:

Couples from the same ethnic group Individuals with a close relative with a genetic

conditionCouples with a history of infertility or miscarriageWomen 35 or older, men 40 or older

Environment

Internal environment – intracellular system of physical and chemica lforces within the cell that influence the genetic materials of the nucleus and the extra cellular systems consisting of the blood and the lymph and the pressures that surrounds the cells.


Pre natal environment Fetus is attached to the mother through

the umbilical cord Developing child is susceptible to the

changing conditions within the mother such as

- nutritional deficiencies

- infections

- chemical changes in maternal blood as a result of maternal emotion states and exposure to radiation


External Environment


Culture Language Customs

Interaction of Heredity and Environment Danidoff (1987) classified into three the

gene-environment interaction

> Passive

> Evocative

> Active


New Advances in the Field of Psychology In-vitro fertilization Mapping of human genome –discovery of

genes causing inherited forms of diseases- cancer, huntingtons’ disease, http://www.bing.com/videos/search?q=huntingtons+Disease&docid=4574519279944137&mid=2EF0B9C936DF96B554362EF0B9C936DF96B55436&view=detail

tuberculosis

homosexuality


Identifying individuals especially criminals – (PCR and DNA FINGERPRINTING)

GENETIC PRE-SCREENING (child sure to be boy

Gene therapy


Determinants of Human Behavior

Documents