Genes

Genes hold a multitude of mysteries that still need to be unwinded. Scientists around the globe find it fascinating to research genes to reveal the past and the future. Genetic studies unravel your ancestral history as well as the diseases one could most likely get. But what is a gene? How do you define genes? Learn about gene structure, gene definition, composition, disorders, and more. 

What is a Gene? 

It is essential to quickly revise the concept of a cell so that you can completely understand –what is a gene. Cells are the building blocks of life—the structural and functional unit of all living things. On average human cells are too small to be seen with naked eyes, and a human body has up to 37.2 trillion cells. Some common examples of human cells you must have come across are red blood cells, ovum, sperm, and neurons, among others. 

Fascinating Facts:

The longest cell in the human body is the neuron/ nerve cell.

The largest cell in the human body is the ovum. 

The smallest cell in the human body is the sperm and the cerebellum’s granule cell.

Within a cell lies the nucleus, and inside the nucleus are chromosomes. Located on chromosomes are tiny structures called genes. So what is a gene?

Gene definition: A gene is a short strand of DNA. It is a unit of hereditary information. 

Gene location: A gene is located on a locus (plural loci). It is a specific position of a gene or a gene marker on a chromosome.

The following gene diagram shows the location and structure of genes. 

gene diagram

Genes serve as instruction manuals and stay within the cells of your body. Every gene carries instructions that influence your traits/ characteristics, such as colour, height, earlobe, hair colour and more. Also, there are different versions of genes for every character/trait. Each offspring inherits a version. But what are these genes’ versions? 

Gene vs Alleles

What are alleles? An allele is a gene’s variant form. Every gene is present at a specific locus in two copies/versions, where one gene copy is inherited from each parent. When the two copies are not the same, they are termed alleles. So alleles represent alternatives for a character/trait. 

An allele can be understood with the help of the following example:

Genes determine your eye colour. So one gene version/ variant/ allele contains instructions for blue eyes while another allele/ version/variant of a gene has instructions for black eyes.

A gene can have more than two alleles, but only two are present at a locus.

Did you Know?

Wilhelm Johannes, a Danish botanist, coined the term gene in 1909. 

Dominant and Recessive alleles: Alleles can result in different phenotypes as certain alleles are dominant over others. A dominant allele of a gene always expresses itself irrespective of the other allele present and decides the phenotype. The alleles that remain suppressed in the presence of the dominant allele are called recessive. They express only in homozygous conditions. 

Homozygous and heterozygous: Every individual has two versions/ alleles or a single gene. When the alleles are the same, the condition is called homozygous, and the individuals are termed homozygotes. When the alleles are different, they are heterozygotes.

In a few conditions, multiple alleles are codominant, i.e., both are dominant and express themselves. For instance, the human ABO blood group system. An individual with AB blood type has one allele for A and one for B. 

Gene Structure and Composition 

What are genes made of? Genes comprise deoxyribonucleic acid (DNA), except in some viruses that have ribonucleic acid (RNA). DNA consists of two nucleotides chains twisted around each other, resembling a twisted ladder. Since a gene is a short section of DNA. It consists of small chemicals called nitrogenous bases. Human genes vary in size ranging from a million bases to a few hundred. The nitrogenous bases come in four types: 

  • Adenine
  • Cytosine
  • Thymine 
  • Guanine  

It is important to note that in some genes, all DNA sequences do not code. The non-coding sections of the DNA/ RNA transcript are called introns. These introns are spliced out before protein synthesis. The coding sections of the DNA (or RNA) are called exons.

Gene vs DNA

DNA is the genetic material that carries information for heredity, mutations, replication process, and distribution of DNA in cell division. Genes are portions of DNA that encode specific proteins and regulate an organism’s traits. 

The following table enumerates the main differences between genes and DNA. 

Gene DNA- Deoxyribonucleic acid
It is a DNA stretch responsible for encoding specific proteins. It is a biomolecule containing genetic information.
Genes regulate an organism’s traits.  DNA regulates gene regulation.
It is a specific sequence on a short DNA. It is two long chains of polynucleotides twisted together.
It is composed of either DNA or RNA. It is composed of nucleotides.
It is present on a chromosome. It is present within the nucleus of the cell.

Gene Functions: What do Genes do? 

  • Genes control DNA and RNA functions. 
  • They form proteins that act as building blocks for muscles, skin, and connective tissue.
  • They regulate enzyme production.
  • Protein synthesis is responsible for almost all activities and is mainly controlled by genes.
  • They contain a set of instructions that control functions.
  • They pass information from parent to offspring. 

Where do you get your genes from? 

You inherit genes from your parents. You get half from your mother and the other half from your father because you get 23 chromosomes from each parent. 

When you inherit genes, you mostly get two variations of each gene, one from either parent. For instance, you inherit two versions of the genes that decide the eye colour. So if you inherit brown-eye genes from your mother and blue-eye genes from your father, you will have brown eyes as the brown-eye genes are dominant over blue-eye genes. 

But what makes you different from your siblings when you share the same parents?

The science of genes is fascinating. It is worth knowing that no one in the world can have the same genes as yours unless they’re your identical twin. So what makes you different from your siblings is the set of genes you inherit from your parents because each of your parents has two versions of each gene. So when they pass their genes onto you, only a version gets transferred, and the process is completely random. 

Genetic Disorders: How Genes Affect Your Health?

The conditions or disorders you inherit from your parents are genetic conditions. These conditions usually run in families. There are more than 10,000 genetic conditions identified. A commonly occurring genetic condition is sickle cell anaemia. In this genetic disorder, the gene causes RBCs to be wrong-shaped (sickle-shaped), making it hard for them to carry oxygen around the body. 

Scientific research has proven that genes influence your risk of developing conditions like diabetes, cancer, Alzheimer’s and more. 

Usually, there are three different ways in which genetic disorders arise:

  • a genetic change occurring spontaneously in the process of egg/ sperm formation or at conception
  • a changed gene passed from parent to offspring that leads to a disorder at the time of birth or later in life
  • a changed gene passed from parent to offspring causes genetic susceptibility to a disorder. It means you are at increased risk of developing the condition when exposed to certain environmental or chemical factors. If you aren’t exposed, the condition might never develop.  

Frequently Asked Questions

Q1. What is gene therapy?

Gene therapy is a treatment option wherein genetic engineering is employed to treat a disease caused by a gene. It involves the modification of an individual’s genes to cure a disease. Often a disease-causing gene is replaced with a healthy copy of the same gene, or the disease-causing gene is inactivated.

Q2. What is genetic counselling? 

Genetic counselling is a process wherein a genetic counsellor gives you information on the possible genetic conditions that can affect you or your family based on your genetic makeup and family health history.

Q3. Who introduced genes?

Gregor Mendel introduced the concept of genes, but he then called genes factors. It was later that Wilhelm Johannsen suggested the term genes for Mendelian factors of inheritance. The word gene has a Greek origin where the word “genos” means birth. 

Q4. What is a cistron?

A cistron is a short DNA segment equivalent to a gene that specifies a single functional unit. It is the smallest genetic material unit that codes for a single polypeptide in protein synthesis. 

Conclusion 

Genes serve as blueprints for our bodies. They carry important instructions, and when a gene changes, the message changes too. Changes can also occur spontaneously in genes. Unwanted changes in genes can also cause a wide range of disorders. Scientists have been introducing ways wherein a correct gene can replace the incorrect one and solve the problem.