Genetics : Studying the Building Blocks of Life

The word genetics stems from the ancient Greek γενετικός genetikos meaning "genitive"/"generative", which in turn derives from γένεσις genesis meaning "origin". Which is very appropriate, because Genetics is the study of heredity or our origin!

Sections:

  1. What is genetics?
  2. Vital parts in the study of genetics
  3. How can the study of genetics be used clinically?

What is Genetics?

Genetics is the term that is used to refer to the study of heredity. Heredity is a biological process where a parent passes on certain genes and traits onto their offspring. By principle, every child inherits genes from both of their biological parents, and these genes in turn manifest themselves in specific traits. These traits may be physical, like skin color or eye color, but on a deeper level, genes may also carry health risks of certain diseases, illnesses and disorders that may be passed on from one generation to the next.

  

Vital parts in the study of genetics

Genes in the cell

Every living being has genetic information that is stored within the cell nucleus of each living cell in the body. Half of the information comes from the mother of the individual, and the other genetic information comes from the father.

Chromosomes

These are small thread-like structures in the nucleus of cells. Genes lie within these chromosomes. Human beings have 23 pairs of chromosomes, 23 of the 46 chromosomes come from the mother, while the other 23 come from the father.

Chromosomes can be regarded as pages from a book. Just like pages in a book, some chromosomes may contain thousands of important genes, and in turn, others might only carry a few. The chromosomes, and therefore genes, are made up of a chemical substance called DNA (DeoxyriboNucleic Acid); chromosomes are very long, thin strands of DNA, coiled and wound up tightly.

Chemical bases

Chemical bases comprising of unique codes of Adenine, Thymine, Cytosine and Guanine further make up the genes. Relating it to the pages of the book analogy, these are akin to the words on the page.

This special part of the DNA act together to form the blueprints and help signal the cells of the body; they tell them when and how to grow, mature and perform various functions. As they age, genes may develop faults and damage due to environmental and endogenous toxins and stress.

Males and females

There are many differences between males and females that are visible to the naked eye, as well as in the genetic makeup. Women have 46 chromosomes, made up of 44 autosomes plus 2 copies of the X chromosome. They have 22 autosomes plus an X chromosome in their egg cells.

Men, on the other hand, have 46 chromosomes, comprised of 44 autosomes plus an X and a Y chromosome in their body cells; they have half of these 22 autosomes plus an X or Y chromosome in their sperm cells.

When the egg cell is met by the sperm, the result is a baby who also has 46 chromosomes, half from the father’s sperm and the other half from the mother’s egg. The offspring will either have an XX, for a female baby, or XY in a male baby.

Genes and genetics

Each gene is a vital piece of genetic information. All the DNA in the cell all add up to make up the human genome. There are about 20,000 genes located in just one of the 23 chromosome pairs found in the nucleus.

At present, over 12,800 genes have been mapped out to specific locations or loci, on each of the chromosomes. The exact number of genes in the human genome is still unknown.

How can the study of genetics be used clinically?

Disease Understanding

The study of genetics has helped shed light on many disorders, sometimes even allowing them to be reclassified. For example, the classification of many spinocerebellar ataxias has been changed from one based on clinical criteria to one based on genetic criteria.

Diagnosis

Many disorders, such as Turner syndrome, Klinefelter syndrome and hemochromatosis among others, can be diagnosed using genetic testing. When a genetic disorder is diagnosed, it often indicates that relatives of the affected person should be screened for the genetic defect or for carrier status. The Genetic Testing Registry offers diagnostic strategies and recommendations for risk counseling, as well as a catalog for genetic tests available.

Genetic Screening

There would be some instances where prenatal genetic screening may be indicated in populations at risk of a particular genetic disorder. The usual criteria that should be met for genetic screening are:

  • Genetic inheritance patterns are known.
  • Effective therapy is available.
  • Screening tests are sufficiently valid, reliable, sensitive and specific, noninvasive, and safe.

On top of this, the prevalence in a defined population must be high enough in order to justify the cost of the screening. One particular aim of prenatal genetic screening is to identify asymptomatic parental heterozygotes carrying a gene for a recessive disorder.

Treatment

As experts will come to better understand the genetic and molecular basis of disorders, it will pave the way to therapeutic solutions. Therapy may involve replacing a deficient compound or blocking an overactive pathway, depending on the findings. Physicians and experts will be able to give recommendations with these bases.

Pharmacogenomics

Pharmacogenomics is a very important science, as it analyzes how genetic characteristics affect the response to drugs. The genetic characteristics of a person may help predict how that individual may respond to treatments. For example, metabolism of warfarin is determined partly by variants in genes for the CYP2C9 enzyme and for the vitamin K epoxide reductase complex protein 1. Genetic variations (eg, in production of UDP [uridine diphosphate]-glucoronosyltransferase 1A1) also help predict whether the anticancer drug irinotecan will have intolerable adverse effects.

Another aspect of pharmacogenomics is pharmacodynamics, this refers to how drugs interact with cell receptors. Genetic and thus receptor characteristics of disordered tissue can help provide more precise targets when developing drugs (eg, anticancer drugs). For example, trastuzumab can target specific cancer cell receptors in metastatic breast cancers that amplify the HER2/neu gene. Presence of the Philadelphia chromosome in patients with chronic myelogenous leukemia (CML) helps guide chemotherapy.

Gene therapy

In a broad scope, gene therapy can be considered any treatment that changes gene function. However, clinically, gene therapy can be used by a patient that suffers from a specific genetic disorder; the insertion of normal genes into the cells of a person who lacks such normal genes can help that person get over his genetic disorder.  The normal genes can be manufactured, using PCR, from normal DNA donated by another individual. Because most genetic disorders are recessive, usually a dominant normal gene is inserted. Currently, such insertion gene therapy is most likely to be effective in the prevention or cure of single-gene defects, such as cystic fibrosis.


References:

Changing the World. One Test at a Time.

© 2018 InSource Diagnostics. All Rights Reserved.