Chapter 1: Physical-Biological Theories

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Deoxyribonucleic acid (DNA)

Chemical inside the cell nucleus that is the molecular basis of heredity; constructed of double helix with parallel strands of both pairs held together by hydrogen bonds.



Threadlike package of genes and DNA in the cell nucleus; contains instructions to make all proteins a living being needs. Humans have 46 chromosomes (23 pairs-44 autosomes and two sex chromosomes).



All the DNA and full set of chromosomes with all the genes they contain, which make up the genetic material of an organism. Each human genome contains about 30,000 genes.



Basic functional and physical unit for transmission of hereditary instructions.


Each gene is a separate

section of the chromosome, and each contains instructions for a specific protein, made up of strings of blocks of amino acids.


Four chemicals,

adenine (A), thiamine (B), guanine (G), and cytosine (C), are found in various combinations.


Each molecule of DNA is made up of

two strands of these chemicals, twisted into a double helix or what looks like a twisted ladder. Each rung is made up of a pair of these chemicals, A-T, T-A, G-C, and C-G. These pairs are arranged in triplets. Each triplet is a genetic code for a specific amino acid.


A gene is a series of

triplets corresponding to the string of 20 amino acids that make up a protein and do the work of the cells. Genes are dominant or recessive, and interact directly or indirectly with many other genes.


Some genes are

“regulator” genes; they direct other genes to guide growth and development and account for genetic differences between humans and animals. In each cell, some genes are expressed while others remain dormant.


A gamete or reproductive cell produces a

new individual when it combines with a gamete from the opposite sex. Each person can produce about 8 million chromosomally different ova or sperm.


Genotype is the person’s

entire genetic inheritance or potential but is not shown outwardly. Every behavioral tendency is affected by many genes, including additive or dominant-recessive patterns.


Phenotype is the person’s

observable appearance and behavior, the result of genetic and environmental influences.


Additive genes

A trait reflects fairly equal distribution of all involved genes, for example, skin color, height, and hair texture or curliness. Additive traits depend on contributions of whichever genes a child inherits (half from each parent). Each additive gene affects the phenotype.


Nonadditive genes

The phenotype shows influence of one gene more than another gene



The phenotype reveals influence of a dominant gene, for example, brown rather than blue eyes.



The phenotype does not reveal that the person carries the gene. For example, brown-eyed parents may have the gene for blue eyes, and their child may have blue eyes.


Sex or X-linked pattern

Genes located on the X chromosome affect the offspring.


Females have

two X chromosomes


males have one

X and one Y chromosome.


In females, a normal dominant gene on the X chromosome from the father generally

overrides a defective gene on the X chromosome from the mother.


Sex-linked recessive traits are carried

on one of the X chromosomes of an unaffected mother. She is a carrier; she does not have the disease but can pass it on to her children.


Whatever recessive gene is inherited on the male

Y chromosome cannot be counterbalanced by the female X chromosome. Thus, recessive genes will be expressed. Traits on the X chromosome can be passed from mother to son, not father to son. Thus, males have more X-linked disorders, for example, red-green color-blindness.


Parental “imprinting” or “tagging” of genes–Certain genes may

behave differently, depending on whether they came from the mother or father. For example, genes for height, insulin production, and some forms of mental retardation affect the child in different or opposite ways, depending on which parent the gene came from.


Mutation–A change in the normal DNA pattern of a particular gene is caused by

environmental factors, including teratogens (agents that produce adverse effects), such as radiation or toxic chemicals. Most mutations are lethal; however, sometimes the person with a mutation may live, thrive, and reproduce. Inherited mutations account for a small number of disorders.


multifactorial disorders, in which effect

of the gene is expressed only if specific other genes are also present in the genotype and influenced by environment as well.


A related concept is multifactorial effects, meaning that

genetic traits are influenced by many factors, including environment. Thus, without genes, no traits or behavior would exist. Without environment, no gene could be expressed


The Principle of Differential Susceptibility suggests that

individual differences in heredity exist that make people susceptible to the influence of certain environments. Given different experiences, a person with certain hereditary potential could develop in different ways.


Susceptibility suggests that individual differences in heredity exist that make people susceptible to

the influence of certain environments. Given different experiences, a person with certain hereditary potential could develop in different ways.


Principle of Differential Exposure suggests that inherited characteristics cause

differing reactions from people, which in turn affect or shape the personality of the individual.


Genomics is the study of the

functions and interactions of all the genes in the genome, including interaction of genes with each other and of genes with the environment, and the relationships among genes, environment, health, and disease.


The Stress-Diathesis Model explains

that numerous genes each create a biological bias toward certain behaviors but do not guarantee those behaviors. Genes produce changes at biological but not behavioral levels. However, the biological changes increase the probability of abnormal behavior or disease, due to combinations of genetic influences with sufficient environmental input