Sickle Cell Anaeamia : Genic Mendelian Abnormalities

Genetic Mendelian Disorder.

It is a Genic Mendelian Abnormalities, which arise due to a recessive gene. According to 'Beadle and Tatum', one or the other enzyme plays its role in each step of metabolism in the body. If any one enzyme is changed or absent in this process, its effect is visible in the form of some disorder or disease. On this basis, 'Beadle and Tatum' presented a hypothesis called 'One Gene, One Enzyme'. Sickle cell anemia is also one such genetic disorder.

Inheritance of Sex Linked Genes

In this way we can say, when a gene is changed or absent in the metabolic process, the condition of the enzymes responsible for the metabolic process is affected. Due to which diseases or ailments arise in humans. The disease caused by the effect of this gene is called genetic Mendelian disorder. There are many types of it like – Sickle Cell Anemia, Phenylketonuria (PKU), Alkaptonuria, Albinism etc.

Sickle Cell Anaeamia

As it is clear from the name, Anemia means lack of blood or blood in the body. There is a lack of blood in the person suffering from this disease. Following are the facts related to this disease –

General Characteristic

• In normal individuals, the dominant gene remains in the homozygous state ( Hb^A Hb^A ), due to which normal hemoglobin is formed. It consists of four polypeptide chains, out of which two chains are alpha chains containing 144 amino acids and two chains are beta chains containing 146 amino acids.
• Sickle cell anemia is a genetic disorder caused by homozygosity of a recessive gene ( Hb^S Hb^S ) .
• In this, the chemical structure of hemoglobin changes, due to which it is unable to carry oxygen.
• In this, the shape of red blood cells changes from round and flat to sickle shaped. Due to which they start sticking together and thus the oxygen transport capacity decreases.
• Due to affecting or reducing the oxygen transport capacity in the person, the cells of the body do not get enough oxygen, due to which the person dies.
• Heterozygous ( Hb^A Hb^S ) individuals are normal. Due to low partial pressure of oxygen in these persons, their red blood cells also become tear-shaped. These people are not able to do physical work.

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Genetic Reason of Sickle Cell Anaeamia

• In the homozygous ( Hb^S Hb^S ) state, abnormal hemoglobin is produced in place of normal hemoglobin.
• Due to the recessive gene, glutamic acid (Glu) is replaced by valine acid (Val) at the sixth position in the beta chain of hemoglobin i.e. in the Hb^S allele, the sixth codon GAG of  Hb^A  is replaced by GUG.
• In this way, the valine (Val) at the first position in the beta chain joins with the valine (Val) at the sixth position. Thus the structure of hemoglobin changes from normal to sickle shaped. That is why it is called Sickle Cell Anaemia.
• The abnormal hemoglobin made above cannot transport oxygen, and the person dies.

Heredity

• Their inheritance is also according to Mendel's law.
• This symptom is found in the ratio of 2: 1 in the offspring born from the union of a male with Hb^A / Hb^S genotype and a female with Hb^A / Hb^S genotype, because the offspring  of Hb^S Hb^S  homozygous do not survive. According to the ratio 2: 1, two children will become carriers of sickle cell anemia due to Hb^A Hb^S, while one child will be normal due to Hb^A Hb^S.

Chromosomal Disorder in Human