Genetic is a branch of biology which deals with principles of inheritance and its practices. Progeny resembling the parents in morphological and physiological features has attracted the attention of many biologists and various disorders related to genetics are founded.
Broadly, genetic disorders may be grouped into two categories – Mendelian disordered and Chromosomal disorders. Mendelian disorders are mainly caused due to alteration or mutation in the single gene. Most common and prevalent Mendelian disorders are Haemophilia, Cystic fibrosis, Colour blindness, Phenylketonuria, Thalassemia, etc.
Let’s take a look at 3 common Mendelian disorders.
This sex-linked recessive disorder, which shows its transmission from unaffected carrier female to some of the male progeny has been widely studied. In this disorder, a single protein that is a part of the cascade of proteins which is involved in the clotting of blood is affected. Because of this, in an affected individual, a simple cut will result in non-stop blood flow. The heterozygous female for haemophilia may spread the disease to sons. The probability of a female becoming haemophilic is very rare because the mother of such a female has to be at least carrier and the father should be haemophilic. The family pedigree of Queen Victoria shows a no. of haemophilic victims as she was a carrier of this disease.
This is an autosome linked recessive trait that can be transmitted from parents to the offspring when both the partners are a carrier for the gene. The disease is controlled by a single pair of the allele, Hb*A and Hb*S. Out of the three possible genotypes only homozygous individuals for Hb*S show the diseased phenotype. Heterozygous individuals appear apparently unaffected but they are a carrier of this disease as there is 50% chance of transmission of the mutant gene to the progeny, thus exhibiting sickle cell trait. The defect is caused by the substitution of Glutamic acid by Valine at the sixth position of the beta globin chain of the haemoglobin molecule. The substitution of amino acid in the globin protein results because of the single base substitution at the 6th codon of the beta-globin gene from GAG to GUG. The mutant haemoglobin molecule undergoes polymerisation under low oxygen tension causing the change in the shape of the Red Blood Cells from biconcave disc to elongated sickle like shape.
This inborn incorrection of metabolism is also inherited as the autosomal recessive trait. The affected individual lacks an enzyme that transforms the amino acid phenylalanine into tyrosine. Because of this phenylalanine is accumulated and converted into phenylpyruvic acid and other derivatives. Accumulation of these in brain causes mental retardation. These are also excreted through urine because of its poor absorption by the kidney.
It is very hard to treat genetic disorders. However, medical science has developed a few methods to treat it partially. For more information regarding genetic disorders, watch the video:
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