What Are Genes, Really? A Beginner’s Dive into Genetics

Genetic health has become one of the most talked-about topics in today’s world. With the rise of personalized medicine and cutting-edge gene therapies, genetics is a rapidly growing field. Still, for many of us, it can feel unfamiliar and even a little intimidating.

What exactly are genes? Where are they located? How do they pass on information from parents to children? And most importantly, what do they actually do?

Let’s explore the fascinating world of genetics in simple terms.

What is Genetics?

Genetics is the study of heredity, the process of one generation passing their genetic material to the next (from parents to children and so on). Many characteristics of the human body are influenced by genes, like weight, height, hair, skin, and eye color, the chance of getting certain diseases (like breast cancer or bleeding disorders), mental health conditions, and even behavioral and personality traits.

What are Genes?

Genes are the biological units of heredity. They are like the blueprint of life, a set of instructions (like an instruction manual) your body needs to perform all its functions, including growth, development, repairing damaged tissues, and making proteins, enzymes, and hormones necessary for everyday function and survival. They are not just responsible for external features but also for the internal workings of your body.

Breaking Down the Blueprint: DNA, Chromosomes & Genes

Overview of how the genetic material (DNA) is packaged inside the body cells.

Our body is made up of trillions of cells. Cells are the building blocks of life, like Lego pieces coming together to form a structure. Each cell contains many different parts that help it function. One of these parts, the nucleus, holds all the genetic material (genome), which is packaged into X-shaped structures called chromosomes.

Chromosomes are made of DNA, a long, thread-like structure that’s tightly coiled, about 2 meters long in each cell! Small segments of DNA are our functional units of heredity: genes. These genes produce proteins (this is called gene expression), which are responsible for various functions in the body. The human genome has around 20,000 to 25,000 genes.

Even though every cell has the same DNA, each type of cell only uses the genes it needs. For example, liver cells and brain cells turn on different sets of genes because they have different jobs and need different proteins. Also, certain genes can be switched on or off as the body grows or in response to things like infections or stress.

Genome: Recipe Book

To simplify these terms: think of the DNA or the genome as a book, the chromosomes as the chapters, and the genes as the recipes.

Human Chromosomes Explained

Diagrammatic representation (karyotype) of the human chromsomes

Most cells in the human body have 23 pairs of chromosomes (46 in total). One pair (X and Y) determines a person's chromosomal or biological sex, while the remaining 22 pairs (numbered 1 to 22) are autosomal (non-sex) chromosomes. Typically, males have 46,XY, and females have 46,XX.

Each chromosome pair carries the same genetic information, meaning each gene has two copies. This is because we inherit half of our genes from each parent, one chromosome from the mother (egg cell) and one from the father (sperm cell).

As shown in the image below, the egg cell (also called an ovum) contains 23 chromosomes, and the sperm has 23 chromosomes. When the egg and sperm fuse (fertilization), they form a zygote, the first cell from which life begins, with 46 chromosomes, or 23 pairs.

To simplify: it’s like mom’s recipe book combines with dad’s recipe book to create a new one for the child, made up of equal parts from both parents.

How chromosomes and genes are passed on during fertilization

How Is a Person’s Chromsomal Sex Determined?

Additionally, during the process of fertilization, the egg cell always contributes an X chromosome. The sperm cell from the father can contribute either an X or a Y chromosome.

• If the sperm provides an X, the baby will have XX → typically, female

• If the sperm provides a Y, the baby will have XY → typically, male

Stay tuned for the next post, where we explore how changes in genes can lead to health conditions, and how these are passed from one generation to the next.

References: 

• Genetics Basics. (2024, May 15). Genomics and Your Health. https://www.cdc.gov/genomics-and-health/about/index.html 

• Genetics. (n.d.). Mount Sinai Health System. https://www.mountsinai.org/health-library/special-topic/genetics 

• Help me Understand Genetics: MedlinePlus Genetics. (n.d.). https://medlineplus.gov/genetics/understanding/ 

• Basic Genetics. (n.d.). https://learn.genetics.utah.edu/content/basics/ 

• Genetic Alliance; The New York-Mid-Atlantic Consortium for Genetic and Newborn Screening Services. Understanding Genetics: A New York, Mid-Atlantic Guide for Patients and Health Professionals. Washington (DC): Genetic Alliance; 2009 Jul 8. CHAPTER 1, GENETICS 101. Available from: https://www.ncbi.nlm.nih.gov/books/NBK115568/

• Professional, C. C. M. (2025, March 19). DNA, Genes & Chromosomes. Cleveland Clinic. https://my.clevelandclinic.org/health/body/23064-dna-genes--chromosomes 

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