Writer: Brain Guo

Genetics is the study of the concept of heredity – the process in which individuals pass biological information to their offspring. These biological characteristics range from traits like height, hair color, and eye color to complex traits like the ability to metabolize certain nutrients or the genetic risk of developing certain diseases (“Genetics”). The study of genetics can therefore investigate each of these aspects of an individual, from the molecule that contains the information about each individual, through to the proteins that contain that information, and into the hereditary rules that dictate the information’s passing from generation to generation.

The molecule that contains the hereditary information is the DNA, or deoxyribonucleic acid. DNA is the genetic material that is contained by individuals from the human species and nearly all of the other organisms that exist on the planet (“What Is DNA?”). Each human body contains DNA in each of its cells, with the majority of the DNA located within the “nucleus” of those cells, and the remainder of the DNA located within the “mitochondria” of those cells (“What Is DNA?”).

Within the DNA are bases that contain the information that dictates an individual’s genetic traits. The bases contain the letters A, T, C, and G, and each individual has a strand of DNA that contains around 3 billion of these bases (“What Is DNA?”). Approximately 99% of the bases in an individual are the same as those of each of their other individuals; it is the order in which those bases are arranged in the DNA that makes each human individual unique. Each base can be identified by its chemical counterpart, as A is paired with T, and C is paired with G (“What Is DNA?”). Each base is also attached to both a sugar and phosphate molecule; these “nucleotides” are arranged into the DNA in a way that creates a structure known as the “double helix” (“What Is DNA?”). The specific properties of the base pairing enable the DNA to accurately copy itself during the process of cell division.

Genes are the units of heredity, and contain the information that allows the human body to perform its biological functions (“What Is a Gene?”). Each human contains between 20,000 and 25,000 of these genes, which contain the information that enables the body to create the proteins necessary to perform its various functions (“Cells and DNA”). Each human also contains 46 different genes, each with two versions of that particular gene; each version of a gene is referred to as an allele (“Genetics Basics”). Because each individual contains two copies of each of their genes, each individual inherits one copy from each parent, and contains two copies of each of their genes.

Within the DNA are genes, and each of the genes is contained within chromosomes (“Cells and DNA”). Humans contain 23 pairs of chromosomes, with 22 of the pair being the same for all individuals, and the remainder of each pair determining the sex of the individual; females have XX chromosomes, while males have XY chromosomes (“Genetics Basics”). Each individual receives one set of chromosomes from each parent, which ensures that each individual contain each of their genes from each parent.

The genes in an individual’s body contain the information that enables the individual’s body to create proteins. Proteins are the substances that perform the vast majority of the biological functions in the body (“How Do Genes Direct the Production of Proteins?”). The information contained in the genes leads to the creation of proteins in two steps: first through the process of transcription, wherein the DNA in the nucleus of the cell is transcribed into RNA (ribonucleic acid) which exits the nucleus of the human body, and second through translation, wherein the RNA contains the information to create proteins by the process of translation by the “ribosomes” in the body’s cells (“How Do Genes Direct the Production of Proteins?”). These proteins contain the same order as the genes, and each perform biological functions within the body.

Individuals use their genes in a regulated manner. While each cell in the human body contains the same amount of DNA and genes as each of the body’s other cells, the body’s cells have different functions, and therefore each utilizes its genes differently (“Genetics 101”). The genes within the body are activated and silenced according to the function that the cell performs; genes necessary to allow that cell to fulfill its role are activated, and genes not necessary to that cell’s function are silenced. Such changes to the activation of the genes are referred to as epigenetic changes.

One form of epigenetics is the placement of a methyl group into the DNA of a gene, which can lead to the silencing of that specific gene (“How Genes Work”). Another form of epigenetic changes is the change to the histone proteins that the DNA wraps around; changing the protein structure can change the accessibility of that DNA’s genes from the body’s cells (“Genetics 101”). Thus, the genes of individuals can be regulated according to environmental factors.

Each individual possesses two copies of each of its genes; each individual’s traits are determined by these two genes. Each copy of a gene is referred to as an allele for that gene (“Genetics Basics”). An individual can have two versions of the same allele; if each version is the same, they are referred to as homozygous for that gene; if each is different, they are referred to as heterozygous (“Genetics Basics”). Each of an individual’s traits are determined by each of those alleles.

The transmission of these traits from parents to their offspring is referred to as inheritance. Each of the genes that determine these traits are inherited from each parent; each individual inherits one copy of each of their genes from their mother, and one copy from their father. For each of these traits, each individual can be homozygous for each trait; if they are homozygous for a gene for which one parent exhibits a certain trait, and one parent does not exhibit that trait, there is a 75% chance that the child will exhibit that same trait (“Genetics”). In contrast, there is only a 25% chance that the child will have each of these traits if each parent is heterozygous for those genes (“Genetics”). Additionally, the traits are also passed according to each sex of the individual; certain traits are only expressed in males because males have only one X chromosome, leading to the expression of X-linked recessive traits in males but not in females, and since males cannot inherit an X-linked gene from their fathers (“Genetics”). These rules of inheritance were discovered by Gregor Mendel over 150 years ago, but are still utilized in the present day by genetic counselors to determine how a human trait may be inherited by their offspring.

Human genetic traits are determined by the variants in the DNA of each individual. These variants are changes in the base sequences within the DNA that is passed to the offspring through the germ cells of an individual (“Genetics Basics”). Most variants are naturally occurring, and are corrected through the body’s natural systems that prevent errors in the DNA; variants that are recognized in the germ cells of an individual can be passed to their offspring (“Genetics Basics”). Most variants have no effect on the traits of an individual. Others are responsible for the diversity of humans, traits such as blood type. The majority of those variants, however, can alter the proteins that are created by the body, and can lead to the development of certain diseases within those individuals in whom the variant’s gene alters the body’s proteins (“Genetics 101”). Additionally, the traits of an individual are determined by both their genes and their environment; factors like diet, exposure to other elements, and general health interact with each individual’s genes and determine their expressed traits (“Genetics 101”). Thus, while an individual’s genetic traits may determine their potentialities for those traits, the environmental factors of the individual’s life will determine whether those traits manifest into the body.

Genetics utilizes the information contained in each individual’s DNA to determine each of their traits, their proteins, their function of each of their cells, their genes, their inheritance of each of those traits from each of their parents, and the mechanisms in which each of those traits are expressed within each individual.

Works Cited

Cells and DNA. Help Me Understand Genetics. MedlinePlus Genetics, National Library of Medicine, www.medlineplus.gov/download/genetics/understanding/basics.pdf. Accessed July 3, 2026.

Genetics. MedlinePlus Medical Encyclopedia. National Library of Medicine, www.medlineplus.gov/ency/article/002048.htm. Accessed July 3, 2026.

Genetics 101. Understanding Genetics: A New York, Mid-Atlantic Guide for Patients and Health Professionals. National Center for Biotechnology Information, NCBI Bookshelf, www.ncbi.nlm.nih.gov/books/NBK115568/. Accessed July 3, 2026.

Genetics Basics. Genomics and Your Health. Centers for Disease Control and Prevention, www.cdc.gov/genomics-and-health/about/index.html. Accessed July 3, 2026.

How Do Genes Direct the Production of Proteins? MedlinePlus Genetics. National Library of Medicine, www.medlineplus.gov/genetics/understanding/howgeneswork/makingprotein/. Accessed July 3, 2026.

How Genes Work. Help Me Understand Genetics. MedlinePlus Genetics, National Library of Medicine, www.medlineplus.gov/download/genetics/understanding/howgeneswork.pdf. Accessed July 3, 2026.

What Is a Gene? MedlinePlus Genetics. National Library of Medicine, www.medlineplus.gov/genetics/understanding/basics/gene/. Accessed July 3, 2026.

What Is DNA? MedlinePlus Genetics. National Library of Medicine, www.medlineplus.gov/genetics/understanding/basics/dna/. Accessed July 3, 2026.