Mendelian Disorders in Humans

Mendelian Disorders in Humans

The Mendelian disorder is different types of genetic disorder in humans. These genetic disorders are mainly caused by the changes or alterations in a single gene or due to the abnormalities in the genome. These conditions will be present since the child’s birth and can be predicted based on the history of a family with the help of a family tree. This process of analysis is called the pedigree analysis.

These genetic disorders are quite rare and may affect one person in every thousands or million. Genetic disorders may be heritable or may not be heritable. Inheritable genetic disorders, it usually occurs in the germ line and in non-heritable genetic disorders, the defects are generally caused by new mutations or due to some changes in the DNA.

For instance: The same disease cancer, may either be caused by an inherited genetic condition, or by a new mutation in some people and even by the environmental causes in some.

Types of Mendelian Genetic disorders

According to the Mendel’s’ laws of inheritance, the different types of genetic disorders include:

  1. Autosomal dominant.
  2. Autosomal recessive.
  3. Sex-linked dominant.
  4. Sex-linked recessive.
  5. Mitochondrial.

The different types of Mendelian disorders can be easily determined from the pedigree analysis.

Few examples of the Mendelian disorder in humans are Sickle cell anemia, color blindness, muscular dystrophy, Thalassemia, cystic fibrosis, skeletal dysplasia, hemophilia, and phenylketonuria are the most common Mendelian disorders.

Let us now discuss few of them.

Hemophilia — This is a type of sex-linked recessive genetic disorders. According to the genetic inheritance pattern, the unaffected carrier mother passing on the syndrome to sons. It is a very rare type of disease among females because for a female to get the disease, the mother should either be hemophilic or a carrier and father must be hemophilic. This is a disorder in which blood doesn’t clot normally as the protein which helps in clotting of blood is affected. Therefore, a person suffering from this disease usually have symptoms of unexplained and excessive bleeding from cuts or injuries. This type of s genetic disorders is caused when the affected gene is located on the X sex chromosomes. Therefore males are more frequently and affected.

Sickle – cell anemia – This is the type of an autosomal recessive genetic disorder. According to the Mendelian genetics, its inheritance pattern follows inheritance from two carrying parents. It is caused when the glutamic acid in the sixth position of the beta globin chain of hemoglobin molecule is replaced by valine. The mutant hemoglobin molecule undergoes a physical change which changes the biconcave shape into the sickle shape. This reduces the oxygen binding capacity of the hemoglobin molecule.

Phenylketonuria – This genetic disorder is autosomal recessive in nature. It is an inborn error caused due to the decreased metabolism level of the amino acid phenylalanine. The affected person does not have the enzyme that converts phenylalanine to tyrosine. As a result, phenylalanine accumulation takes place in the body and converted into many derivatives which result in mental retardation.

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Practise This Question

Choose the correct option regarding the Assertion and Reason:

Assertion [A]: Turner syndrome occurs only in females.

Reason [R]: Turner syndrome is characterised by X0 sex chromosomes.