Genetic diseases and disorders

Genetic diseases and disorders

What is genetics?

Genetics studies how individual genes or groups of genes are involved in health and disease. Understanding genetic factors and genetic diseases is important to learn more about health promotion and disease prevention.

Certain genetic changes have been associated with an increased risk of having a child with a birth defect or developmental disability or developing diseases such as cancer or heart disease. Genetics can also help us understand how medical conditions occur.

How we inherit our genes

People inherit their own chromosomes, which contain their genes, from their parents. Chromosomes are in pairs and humans have 46 chromosomes, in 23 pairs. Babies randomly receive one of each pair of chromosomes from their mother and one from each pair from their father. The chromosomes that make up the 23rd pair are called sex chromosomes. They decide whether a person is born male or female. A female has two X chromosomes and a male has one X chromosome and one Y. Each daughter receives an X from her mother and an X from her father. Each child receives an X from his mother and a Y from his father.

Genetic diseases

Genetic disorders can occur for many reasons. Genetic disorders are often described in terms of the chromosome that contains the gene that is changed in people who have the disorder. If the gene is located on one of the first 22 pairs of chromosomes, called autosomes, the genetic disorder is called an autosomal condition. If the gene is on the X chromosome, the disorder is called X-linked.

Genetic disorders are also grouped according to the way they run in families. Disorders can be dominant or recessive, depending on how they cause conditions and how they manifest in families.


Dominant diseases can be caused by only one copy of a gene that has a DNA mutation. If one parent has the disease, each child has a 50% chance of inheriting the mutated gene.


For recessive diseases, both copies of a gene must have a DNA mutation to obtain one of these diseases. If both parents have one copy of the mutated gene, each child has a 25% chance of having the disease, even if neither parent has it. In such cases, each parent is called a carrier of the disease. They can pass the disease on to their children, but they don’t have the disease.

Single gene disorders

Some genetic diseases are caused by a DNA mutation in one of a person’s genes. For example, suppose that a part of a gene usually has the CT sequence. A mutation can change the sequence in TTC in some people. This sequence change can change the way the gene works, for example by modifying the protein produced. Mutations can be passed on to a child from his parents. Or they can happen for the first time in the sperm or egg, so that the baby has the mutation but the parents do not. Diseases of a single gene can be autosomal or X-linked.

For example, sickle cell disease is an autosomal single-gene disorder. It is caused by a mutation in a gene found on chromosome 11. Sickle cell anemia causes anemia and other complications. Fragile X syndrome, on the other hand, is a single-gene disease linked to X. is caused by a change in a gene on the X chromosome. It is the most common known cause of intellectual disability and developmental disabilities that can be inherited (passed from one generation to the next).

Chromosomal abnormalities

Different number of chromosomes

People usually have 23 pairs of chromosomes. But sometimes a person is born with a different number. Having an extra chromosome is called a trisomy. The lack of a chromosome is called monosomy.

For example, people with Down syndrome have an extra copy of chromosome 21. This extra copy changes the normal development of the body and brain and causes intellectual and physical problems to the person. Some disorders are caused by having a different number of sex chromosomes. For example, people with external Turnericona syndrome usually have only one sex chromosome, an X. Women with Turner syndrome may have growth problems and heart defects.

Changes in chromosomes

Sometimes chromosomes are incomplete or have a different shape than usual. The lack of a small part of a chromosome is called deletion. A translocation is when a part of a chromosome has moved to another chromosome. A reversal is when a part of a chromosome has been turned upside down.

For example, people with Williamsicon syndrome are missing a small part of chromosome 7. This deletion can cause intellectual disability and a distinctive appearance and personality of the face.

Complex conditions

A complex disease is caused by both genetic changes and environmental factors . Complex diseases are also called multifactorial. Most chronic diseases, such as heart disease, cancer, and diabetes, are complex conditions. For example, while some cases of cancer are associated with inherited genetic changes, for example, hereditary Lynch syndrome and breast cancer and ovarian cancer, most are most likely caused by changes in the different genes that act together with environmental exposures.

Katherine Johnson, M.D., is a board-certified obstetrician-gynecologist with clinical expertise in general obstetrics and gynecology, family planning, women’s health, and gynecology.

She is affiliated with the Obstetrics and Gynecology division at an undisclosed healthcare institution and the online platform,

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