Genetic Disorders Study Guide


Chromosomes consist of a strand of DNA wrapped around a protein called histones and segregated in two halves by a centromere. Chromosomes carry important genetic information and if this information is incorrect, it can give rise to a lot of illnesses that are characterised as genetic disorders.

Genes carry all the unique genetic information in alphabetic codes called nucleotides. The genetic code is responsible for all of the unique information passed down from generation to generation. There are around 3 billion genes in the DNA that replicate perfectly during the complex process of cell division. The passing of information during replication is done through enzymes and a molecule called mRNA.

Given how critical genes are to our bodies, it is easy to imagine that if there is a distortion in chromosomes or genetic information, it can lead to genetic disorders and genetic diseases.

For example, if there is an extra 21st chromosome, it can lead to Down syndrome. Similarly, if the genetic information about protein synthesis is incorrectly transferred, it can lead to the origin of cancerous cells. This guide touches upon genetic disorders that can affect our bodies.

Types of genetic disorders

Most genetic disorders in humans are caused due to faulty transmission of reproductive cells. We can classify the genetic disorders in four categories:

i) Single gene inheritance

ii) Multifactorial inheritance

iii) Chromosome abnormalities

iv) Mitochondrial inheritance

1. Single Gene Disorders

Genetic disorders caused by mutations

Single gene disorders are caused due to mutation in the DNA sequence of a single gene. This is also known as Mendelian or monogenic inheritance. Today, we have thousands of known single-gene disorders. Let’s look at some of the patterns of single-gene disorders:

  • Autosomal Dominant Inheritance: In this condition, only one defective gene from any of the parents is enough to cause the disorder.
  • Autosomal Recessive Inheritance: In this condition, two defective genes (one from each parent) are required to cause the genetic disorder.
  • X-linked Inheritance: In this condition, the defective gene is present in the female. That is to say; the defective gene is present on the X-chromosome. X-linked inheritance can go both ways; it can be dominant or recessive.

Now, let’s look at some of the examples of single genetic disorders list:

i) Alpha and Beta Thalassemias

ii) Cystic Fibrosis

iii) Marfan Syndrome

iv) Sickle cell anemia

v) Fragile X Syndrome

vi) Hemochromatosis

vii) Huntington’s Disease

2. Multifactorial Genetic Inheritance Disorders

This is a complex genetic disorder where more than one gene is affected. Also, the disease caused is due to a combination of faulty genes and several other environmental factors.

For example, breast cancer is found on chromosome numbers 6, 11, 13, 14, 15, 17, and 22. Therefore, we can conclude that multifactorial genetic inheritance disorders are caused due to mutation in multiple genes. Let’s look at some of the diseases caused to multifactorial inheritance:

i) Alzheimer’s disease

ii) Heart disease

iii) High blood pressure

iv) Diabetes

v) Arthritis

Multifactorial genetic inheritance disorders

Further, multifactorial inheritance can also be linked to unique traits such as height, eye color, fingerprint patterns, and skin color.

3. Chromosomal Abnormalities

We know that every human has 23 pairs of chromosomes, which is 46 in total. Therefore, every human inherits 23 chromosomes from each parent. Now, chromosomes are present in the nucleus of every cell and are made of protein and DNA. Chromosomes also play an active role in cell division.

Also, single pair chromosomes are present in the gametes, which pair up with the other 23 chromosomes to make a single complete chromosome in a cell. If there are irregularities in the chromosome number, it can lead to chronic diseases because chromosomes also carry genetic information.

In the case of Down syndrome or Down’s syndrome, as some may call it, there are three pairs of 21st chromosomes. Now, let’s look at a genetic diseases list caused due to chromosomal abnormalities:

i) Klinefelter Syndrome (47, XXY)

ii) Turner Syndrome (45, X0)

iii) Cry of the cat syndrome

Chromosomal translocation is also one of the reasons that can cause the disorders mentioned above.

4. Mitochondrial Genetic Inheritance Disorder

Severity of mitochondrial disease in a child

We know that mitochondria are the powerhouse of the cell. It is present in every cell and accounts for respiration. Mitochondria are located in the cytoplasm of every plant and animal cell.

Each mitochondrion has its DNA with 15-20 circular chromosomes. Now, mitochondrial genetic inheritance disorder is caused due to the genetic mutation in the mitochondrial DNA.

Since mitochondria are retained by the egg cell only, it is passed on from the mother only. Now, let’s look at some diseases caused by mitochondrial genetic inheritance:

i) Myoclonic epilepsy with ragged red fibers (MERRF)

ii) Leber’s hereditary optic atrophy (LHON), an eye disease

iii) Mitochondrial Encephalopathy, lactic acidosis, and stroke-like episodes (MELAS), a rare form of dementia.


  • Genetic disorders are caused due to genetic mutations.
  • There are three types of genetic disorders.
  • There can be thousands of genetic disorders as of now, but the most common ones have been discussed above.


1. What are the ten genetic disorders?

Let’s define genetic disorders first. Genetic disorders are caused due to genetic mutations in humans during inheritance. It hampers the protein synthesis information that leads to chronic diseases. Now, there are a thousand genetic diseases but let’s look at a list of genetic disorders that are quite common:

  • Down Syndrome
  • Cystic fibrosis
  • Huntington’s disease
  • Duchenne Muscular Dystrophy
  • Sickle cell anemia
  • Haemophilia
  • Thalassemia
  • Fragile X syndrome

2. Is autism a genetic disorder?

We can relate autism to some genetic mutations. Fragile X syndrome, in some cases, is responsible for autism. However, in most cases, genetic mutations only increase the risk of autism.

3. What are the three types of genetic disorders?

As discussed earlier, three types of genetic disorders are:

i) Single gene inheritance disorder

ii) Multifactorial genetic inheritance disorder

iii) Mitochondrial genetic inheritance disorder

4. Is bipolar a genetic disorder?

There are several instances of inheritance of bipolar disorder. In 80% of the cases, bipolar disorder was passed down in the family. Also, if one of the parents has this disease, there is a 10% risk of inheriting it.

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