The Mendelian disorder is one of the types of genetic disorder in humans. The Mendelian disorders arise from the change or alteration in a single gene. Their genetic inheritance is governed by the Mendelian genetics. They 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. Sickle cell anemia, color blindness, Cystic fibrosis, hemophilia, Thalassemia, and phenylketonuria are the most common Mendelian disorders.
Mendelian Genetic Disorders
These Genetic disorders are basically of four types:
- Autosomal dominant
- Autosomal recessive
- Sex-linked dominant
- Sex-linked recessive
We can easily determine the types of Mendelian disorders from the pedigree analysis.
Let us now discuss a few examples:
- Haemophilia – It is a sex-linked recessive disease. Its genetic inheritance pattern shows unaffected carrier mother (heterozygous) passing on the disease to sons. It is a very rare disease among females because for a female to get the disease, the mother should either be hemophilic or carrier and father must be hemophilic. In this disease, the protein which helps in clotting of blood is affected. As a result of this, a person suffering from the disease does not stop bleeding once he gets a cut somewhere.
- Sickle – cell anemia – This is an autosomal recessive disease. Hence, according to Mendelian genetics, It’s 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. 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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