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 NU 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

GENES, CHROMOSOMES, AND GENETIC CODE:

THE NORMAL CELL

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 membrane.

The cell membrane surrounds the cytoplasm.

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

The nucleus plays an important role in heredity and cell division.

Heredity is what you "inherit" from your parents through your genes. (Genes are found in chromosomes.)

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 meiosis.

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 cancer.

GENES AND CHROMOSOMES

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 pairs.

What Is a Gene?A gene is a distinct portion of a cell’s DNA. Genes are coded instructions for making everything the body needs, especially proteins. Human beings have about 25,000 genes. Researchers have discovered what some of our genes do, and have found some that are associated with disorders (such as cystic fibrosis or Huntington’s disease). There are, though, many genes whose functions are still unknown.

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).

CHROMOSOME ABNORMALITIES

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 (trisomy).

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 two).

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 exchanged.

Inversions: A portion of the chromosome has broken off, turned upside down and reattached, therefore the genetic material is inverted.

Insertions: A portion of a chromosome has broken off and attaches to another chromosome.

How do chromosome abnormalities happen?

Chromosome abnormalities usually occur when there is an error in cell division. There are two kinds of cell division, mitosis and meiosis.

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 chromosome abnormalities

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 younger women. Since men produce new sperm throughout their life, paternal age does not increase risk of chromosome abnormalities.

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 errors.

GENETIC DISORDERS

A. SINGLE GENE DISORDERA single gene disorder is the result of a single mutated gene. Over 4000 human diseases are caused by single gene defects. Single gene disorders can be passed on to subsequent generations in several ways.

Non-X-linked Inheritance/Autosomal (Dominant and Recessive Disorders)

X-Linked Inheritance (Dominant and Recessive Disorders)

Y-Linked InheritanceMitochondrial Inheritance

Definition of Terms

Autosomal: the gene responsible for the phenotype is located on one of the 22 pairs of autosomes (non-sex determining chromosomes).

X-linked: the gene that encodes for the trait is located on the X chromosome.

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).

Non-X-linked (Autosomal)Dominant Inheritance

Non–X-Linked (Autosomal) Recessive Inheritance

X- linked Inheritance (Dominant Disorder)

X-linked Inheritance(Recessive Disorder)

Prevalence of some single gene disorders

Autosomal dominant Familial hypercholesterolemia 1 in 500 Polycystic kidney disease 1 in 1250 Neurofibromatosis type I 1 in 2,500 Hereditary spherocytosis 1 in 5,000 Marfan syndrome 1 in 4,000 Huntington's disease1 in 15,000

Autosomal recessive Sickle cell anaemia 1 in 625 Cystic fibrosis 1 in 2,000 Tay-Sachs disease 1 in 3,000 Phenylketonuria 1 in 12,000 Mucopolysaccharidoses 1 in 25,000 Lysosomal acid lipase deficiency 1 in 40,000 Glycogen storage diseases 1 in 50,000 Galactosemia 1 in 57,000

X-linked Duchenne muscular dystrophy 1 in 7,000 Hemophilia 1 in 10,000

Y-linked Inheritance

Mitochondrial Inheritance

B. MULTIFACTORIAL AND POLYGENIC (COMPLEX) DISORDER

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 environmental factors.

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 disorders.

Examples of Multifactorial and Polygenic (Complex) Disorders:

asthma autoimmune diseases such as multiple sclerosis cancers cleft palate diabetes heart disease hypertension inflammatory bowel disease mental retardation mood disorder obesity refractive error

TESTING FOR CHROMOSOMAL AND GENETIC ABNORMALITIES

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.

PREVENTION

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“.

THANK YOU!!!