Genes, Chromosomes and Genetic Code: Relevance and Implications
RELEVANCE AND IMPLICATIONS
P R E P A R E D B Y : J E N N I F E R C . G R A G E R A , R N
U N I V E R S I T Y O F N O R T H E R N P H I L I P P I N E S
M A S T E R O F A R T S I N N U R S I N G
AND GENETIC CODE:
THE NORMAL CELL
Healthy cells have a structure determined by their
DNA. They need energy to exist and thrive, which
they derive from chemicals in the food you consume.
Cells need a system to deliver nutrients such as
amino acids, carbohydrates, fats, vitamins, and
minerals to them. This system is the body's network
of blood vessels. Growth factors take a cell from birth
(mitosis and meiosis) to death (apoptosis), all the
while helping it to function normally.
The Parts of a Cell
Cells have two main parts, the cytoplasm and the nucleus.
The cytoplasm surrounds the nucleus, much the way the
white surrounds the yolk in an egg.
The nucleus is separated from the cytoplasm by the nuclear
The cell membrane surrounds the cytoplasm.
The cytoplasm contains many organelles. Organelles are like
tiny organs. Each has specific jobs to do within the cell.
Some of the important organelles are:
The endoplasmic reticulum helps make protein.
The golgi apparatus helps move materials out of the cells in
which they are made.
Mitochondria make energy needed for cell function.
Lysosomes digest substances brought into the cell.
The substance surrounding organelles within the cytoplasm
is known as the cytosol.
The nucleus plays an important role in heredity and
Heredity is what you "inherit" from your parents
through your genes. (Genes are found in
Cell division is how new cells are made.
Two Types of Nuclei/Two Types of Cells
Somatic cells - cells that make up the body
contain the usual 46 chromosomes.
Gametes - sex cells (the egg and sperm)
contain only 23 chromosomes. That's half
the number found in somatic cells.
How Cells Divide?
There are two types of cell division, mitosis and
Mitosis is how somatic cells divide.
Meiosis is how sex cells divide.
What Makes Cells Divide?
Growth factors in the blood or produced by cells stimulate cells to divide.
Certain genes in the cell then turn the cell "on" so that division can
happen. After the cell has divided, other genes turn the cell "off" again.
The chain of events is as follows:
Growth factors attach to the cell membrane. They turn "on" messenger
substances within the cell.
The messengers send signals to the nucleus of the cell.
Genes in the nucleus turn "on" the division process.
The DNA in the nucleus replicates (doubles).
The cell divides.
Genes in the nucleus turn the cell "off."
Changes (mutations) in the genes can affect their ability to turn the
cells "on" or "off." This can cause uncontrolled cell growth and
Normal Cells vs Cancer Cells
NORMAL CELLS CANCER CELLS
Structure Have DNA in their genes and
chromosomes that functions normally.
Divide in an orderly way to produce
more cells only when the body needs
Develop an aberrant DNA or gene
structure or acquire abnormal
numbers of chromosomes.
Continue to be created without
control or order. Excess cells form
a mass of tissue called a tumor.
Energy Derive most of their energy using
Derive most of their energy in the
absence of oxygen.
Blood Vessels Have a built-in blood vessel system. Lack a built-in blood vessel
system. They require more of
certain amino acids to grow.
Growth Factors Operate at a normal metabolic level and
reproduce themselves at a regulated
Are overactive and overproduce
themselves, thus requiring more
Functions Have enzymes and hormones that
behave in a balanced manner.
Have either overactive or
underactive enzymes and
What Is DNA?
DNA (deoxyribonucleic acid) carries the genetic information in the
body’s cells. DNA is made up of four similar chemicals (called bases
and abbreviated A, T, C, and G) that are repeated over and over in
What Is a Gene?
A gene is a distinct portion of a cell’s DNA which controls a specific
What Are Chromosomes?
Genes are packaged in bundles called chromosomes. Humans have 23
pairs of chromosomes (for a total of 46). Of those, 1 pair is the sex
chromosomes (determines whether you are male or female, plus some
other body characteristics), and the other 22 pairs are autosomal
chromosomes (determine the rest of the body’s makeup).
There are three types of genetic disorders:
Multifactorial and Polygenic (Complex)
A chromosome abnormality reflects an abnormality of chromosome number
or structure. There are many types of chromosome abnormalities.
However, they can be organized into two basic groups:
a. Numerical Abnormalities
When an individual is missing either a chromosome from a pair
(monosomy) or has more than two chromosomes of a pair
An example of a condition caused by numerical abnormalities is
Down Syndrome, also known as Trisomy 21 (an individual with
Down Syndrome has three copies of chromosome 21, rather than
Turner Syndrome is an example of monosomy, where the individual
- in this case a female - is born with only one sex chromosome, an X.
b. Structural Abnormalities:
Deletions: A portion of the chromosome is missing or deleted.
Duplications: A portion of the chromosome is
duplicated, resulting in extra genetic material.
Translocations: Segments from two different chromosomes are
Inversions: A portion of the chromosome has broken off, turned
upside down and reattached, therefore the genetic material is
Insertions: A portion of a chromosome has broken off and
attaches to another chromosome.
How do chromosome abnormalities
Chromosome abnormalities usually occur when
there is an error in cell division.
In both processes, the correct number of
chromosomes is supposed to end up in the resulting
cells. However, errors in cell division can result in
cells with too few or too many copies of a
chromosome. Errors can also occur when the
chromosomes are being duplicated.
Other factors that can increase the risk of
Maternal Age: Women are born with all the eggs they
will ever have. Therefore, when a woman is 30 years
old, so are her eggs. Some researchers believe that errors
can crop up in the eggs' genetic material as they age over
time. Therefore, older women are more at risk of giving
birth to babies with chromosome abnormalities than
Environment: Although there is no conclusive
evidence that specific environmental factors cause
chromosome abnormalities, it is still a possibility that the
environment may play a role in the occurence of genetic
SINGLE GENE DISORDERS
A single gene disorder is the result of a single mutated gene.
Single gene disorders can be passed on to subsequent
generations in several ways.
Non-X-linked Inheritance/Autosomal (Dominant and
X-Linked Inheritance (Dominant and Recessive Disorders)
Definition of Terms
Autosomal: the gene responsible for the phenotype is
located on one of the 22 pairs of autosomes (non-sex
X-linked: the gene that encodes for the trait is located on the
Dominant: conditions that are manifest in heterozygotes
(individuals with just one copy of the mutant allele).
Recessive: conditions are only manifest in individuals who
have two copies of the mutant allele (are homozygous).
MULTIFACTORIAL AND POLYGENIC
Genetic disorders may also be
complex, multifactorial, or polygenic, meaning they
are likely associated with the effects of multiple
genes in combination with lifestyles and
Although complex disorders often cluster in
families, they do not have a clear-cut pattern of
inheritance. This makes it difficult to determine a
person’s risk of inheriting or passing on these
TESTING FOR CHROMOSOMAL AND
A person's chromosomes and genes can be evaluated
by analyzing a sample of blood.
In addition, doctors can use cells from amniocentesis
or chorionic villus sampling to detect certain
chromosomal or genetic abnormalities in a fetus.
If the fetus has an abnormality, further tests may be
done to detect specific birth defects.
Although chromosomal abnormalities cannot be
corrected, some birth defects can sometimes be
prevented (for example, taking folate [folic acid] to
prevent neural tube defects or screening parents for
carrier status of certain genetic abnormalities).
Did you know…
Not all gene abnormalities are purely harmful – the
gene that causes sickle cell disease also provides
protection against malaria.
"All human disease is genetic in origin."
Paul Berg was awarded one-half of the 1980 Nobel
Prize in Chemistry. He was recognized for "his
fundamental studies of the biochemistry of nucleic
acids, with particular regard to recombinant DNA“.