Key takeaways
- Genes are made of deoxyribonucleic acid (DNA), which contains sequences of four nucleotide bases (adenine, cytosine, guanine, and thymine) that act as biological instructions for making proteins.
- These proteins determine physical traits like eye color and height, and they can also affect a person’s risk of developing genetic conditions such as sickle cell anemia or Huntington’s disease.
- The Human Genome Project (HGP) identified around 20,000 protein-coding genes in humans and discovered more than 1,800 genes that can cause disease, leading to genetic tests that help diagnose conditions and guide personalized treatment.
Genes are made of DNA, which determines an organism’s appearance, survival, and behavior in its environment. All living beings have genes that can affect a person’s health throughout their life.
Different organisms have different numbers of genes. The human genome, which comprises all human genes, contains about
All humans are
These differences, which may be inherited or result from interactions between a person’s genes and the environment, can also explain why some people develop certain diseases, and others do not.
A geneticist is a person who studies genes and how to target them to improve specific aspects of life. Genetic engineering can provide a range of benefits, including preventing some human diseases.
Medical illustration by Bailey Mariner
Genes are
Chromosomes, which are located in each cell’s nucleus, contain genes, and each gene contains DNA sequences that act as instructions for making specific proteins.
These proteins regulate the expression of specific physical characteristics, such as hair color, height, and eye color. They can also determine a person’s risk of having or developing certain genetic conditions.
DNA passes from adult organisms to their offspring during reproduction. This means that people inherit their gene-containing chromosomes from their parents.
Chromosomes come in pairs, and humans have
A gene consists of DNA, and DNA itself comprises four different chemical building blocks, known as nucleotide bases, including:
- adenine (A)
- cytosine (C)
- guanine (G)
- thymine (T)
The DNA molecule has two strands that wind around each other, and each strand is held together by
- A with T
- C with G
The sequence of these bases determines the instructions that exist in a DNA strand. For example, the sequence ATCGTT
Human chromosomes range in size from about
Genes affect hundreds of internal and external factors, from specific eye colors to the types of diseases people may develop.
Changes in genes can sometimes lead to mutations that, in turn, can cause genetic disorders, such as sickle-cell anemia and Huntington’s disease. Because genes pass down from parents to children, these and similar conditions tend to run in families.
Gene mutations can also occur due to exposure to
Diploid refers to an organism with
One set of chromosome pairs
Two of the chromosomes, called the X and Y chromosomes, determine an embryo’s biological sex as male or female.
Chromosome distribution
Females have two X chromosomes
Males have one X and one Y chromosome
All embryos begin with a female parent providing the X chromosome. The male parent will then contribute an X or a Y chromosome to determine biological sex.
The remaining 22 chromosomes are called autosomal chromosomes, which scientists refer to as chromosomes 1 through 22.
There are many different gene types, but some of them include:
- Protein-coding genes: These genes transcribe messenger RNA (mRNA) into proteins. They perform most cellular processes.
- Non-coding genes, also called RNA genes: These genes produce functional RNA molecules (such as tRNA or rRNA) but do not encode proteins. They can lead to diverse biological effects by regulating protein expression and activity at multiple levels.
- Housekeeping Genes: These genes are constantly active and maintain basic cellular functions, such as metabolism.
- Regulatory Genes: These genes turn other genes “on” or “off”.
- Dominant Genes: Genes are called dominant when a person has only one copy from each parent. An example is the “brown eye” gene. If an individual has a “blue eye” gene and a “brown eye” gene, they will have brown eyes, as the “brown eye” gene is dominant.
Recessive Genes: These genes only display their traits if an individual inherits two copies — one from each parent.
By doing this, scientists hoped to develop powerful tools to understand the genetic factors in human disease and to open the door to new diagnostic, treatment, and preventive health strategies.
Scientists completed the HGP in 2003, and all the generated data are available online for free.
Apart from humans, the HGP also looked at other organisms and animals, such as the fruit fly and E. coli.
Scientists have discovered more than three billion nucleotide combinations, or combinations of ACGT, in the human genome. They also discovered more than
This is based on 2015 data, so there may be more scientific developments today.
The
Genetic testing can also look for changes, or mutations, in a person’s DNA that may put them at risk for a specific disease and help healthcare teams diagnose the conditions.
Doctors may use genetic testing for various reasons, including:
- to identify genetic conditions in unborn babies
- to screen newborn babies for certain treatable conditions
- to lower the risk of genetic diseases in embryos created using assisted reproductive technology
- to find out if a person carries a gene for a disease that could be passed on to a child
- to see if a person is at an increased risk of developing a certain disease
- to help a healthcare team decide the best medication and dosage for a person. This is known as pharmacogenomic testing.
Scientists
In recent years, geneticists
DNA holds the instructions for building proteins in the body. These proteins are responsible for numerous cellular functions.
The epigenome comprises chemical compounds and proteins that can bind to DNA and direct a range of activities. These actions include turning genes on and off, which can control protein production in specific cells and alter gene expression.
Gene switches can turn genes on and off at different times and for different lengths of time. The differences among cells are determined by when and how different sets of genes are turned on or off in different cells.
Gene marking
When epigenomic compounds bind to DNA in the cell and modify its function, they have
The marks do not change the DNA sequence, but they do alter how cells use its instructions.
The marks can be passed from cell to cell as they divide and even from one generation to the next.
Specialized cells can control many functions in the body. For example, specialized red blood cells produce proteins that carry oxygen throughout the body. The epigenome controls many of these changes within the genome.
Chemical tags on DNA and histones, which are proteins that support the structure of a chromosome, can rearrange as specialized cells, and the epigenome changes throughout a person’s lifetime.
Lifestyle and environmental factors, such as smoking, diet, and infectious diseases, can alter the epigenome by exposing a person to pressures that prompt chemical responses.
These responses can lead to direct epigenomic changes, some of which can be damaging, resulting in human diseases from malfunctions in proteins that “read” and “write” epigenomic marks.
For example, cancer can result from changes in the genome, the epigenome, or both. Changes in the epigenome can switch genes involved in cell growth or the immune response on or off. These changes can cause uncontrolled growth, a feature of cancer, or a failure of the immune system to destroy tumors.
Researchers in epigenomics are focused on charting the locations and understanding the functions of all the chemical tags that mark the genome. This information may lead to a better understanding of the human body and knowledge of ways to improve human health.
Gene therapy
Gene therapy is a medical technique
Gene therapy often works by adding copies of a broken gene or by replacing a defective or missing gene with a healthy version.
Gene therapy is still in its early stages. However, scientists are using it to treat inherited diseases such as hemophilia and sickle cell disease, as well as acquired disorders such as leukemia.
Gene testing to predict cancer
Another use of genetic information is to help predict who is likely to develop a disease like early onset Alzheimer’s disease and breast cancer.
For example, females with the BRCA1 gene have a significantly higher chance of developing breast cancer. Females can have a test to find out whether they carry that gene.
BRCA1 carriers have a
Genetic tests for personalized therapy
Genetic testing can help doctors determine which medications are best for specific patients based on their genetic makeup. This is called
It looks for gene changes that can help determine which medications or doses are appropriate for a patient. Doctors can also use it to predict if a person could have a serious side effect from a medication.
The following are answers to some common questions about genes.
A gene is a basic unit of inheritance passed on from male and female parents to their children.
Genes contain DNA, which is made up of sequences that determine a person’s physical and biological traits.
Genes are the building blocks of life. They contain information for making specific molecules and proteins that allow human cells to function and that control how the body grows and operates.
They also lead to the expression of specific physical characteristics, such as hair or eye color.
Genes are made of DNA, which contains instructions for producing molecules called proteins.
These proteins are responsible for characteristics such as eye color, blood type, and height.
Genes can also determine a person’s risk of having or developing certain diseases, such as breast cancer or sickle cell anemia.
The Human Genome Project (HGP) has estimated that humans have 20,000 protein-coding genes.
Genes are a set of instructions passed down from parents to offspring. They contain the information that determines a person’s specific physical and biological characteristics.
Genes are made of sections of DNA, and DNA is composed of chemical building blocks called nucleotides. A gene consists of four nucleotide bases, which can be sequenced in different ways to determine different instructions that account for various physical traits, like having blue or brown eyes.
Most genes code for specific proteins that perform different functions throughout the body, allowing humans to live, grow, and reproduce.
Changes in genes can lead to incorrectly formed proteins that can’t function correctly. These are called gene mutations and may lead to genetic disorders.
Researchers continue to study many different areas of genetics, including genetic testing, which can help identify changes in a person’s DNA that may indicate whether they are at risk of developing a disease or passing one to their children.