Explain the cause of chromosomal disorders in humans. Describe the effect of such disorders with the help of an example each involving (i) autosomes, and (ii) sex chromosomes.

A chromosomal disorder is a condition rise due to an unusual number or characteristic of chromosomes in humans. Mostly it’s caused by the number of chromosomes; these changes are not inherited but occur randomly during the formation of reproductive cells. This becomes dominant when each cell in the individual body has one lost or extra chromosome. Changes in chromosome structure can also induce chromosomal disorders. Some changes in chromosome structure can be inherited, while others occur as randomly during the formation of reproductive cells or in early fetal development.
(i) Each cell in the human body has DNA and is made up of 23 pair of chromosomes present inside the cell nucleus. The 22 pair of chromosomes called autosomes, and the balance one and the final pair is called sex chromosome. Autosomes transfer genetic information from the parents to the offspring. During mitosis, these chromosomes are duplicated and transferred to two daughter cells and the new daughter cells get a complete representation of chromosomes containing the genetic information from the parent cell. Although autosomes are not sex chromosomes they contain a few genes that determine gender.

Sickle cell anaemia is another of the most common, inherited, single-gene disorders. Sickle cell disease is caused by a mutation in the hemoglobin-Beta gene found on chromosome 11. This condition is an autosomal recessive pattern, which means both copies of the gene in each cell have mutations. The parents of an individual with an autosomal recessive condition, each carry one copy of the mutated gene, but they typically do not show signs and symptoms of the condition and they act as a carrier and the disease is apparent in the offspring. Sickle cell disease primarily affects red blood cells, and it alters the oxygen-carrying ability of the cell. The normal RBC is smooth, round and flexible while in the diseased condition it becomes sickle and sticky. An identical shape is formed when it loses oxygen-binding ability.

(iii) . The 23rd pair of chromosomes present in humans is called the allosomes (sex chromosome). They differ in size and function when compared to autosomes. They determine the sex of an individual. They are denoted using letters X and Y. Allosomes in females contain XX chromosomes, and in male, it contains XY chromosome. The unusual mixture of allosomes results in disorders like color blindness and haemophilia.

Haemophilia is a bleeding disorder that slows the blood clotting process. People with this condition experience prolonged bleeding following an injury. There are 2 types of haemophilia A and B, although these two types have similar signs and symptoms, which caused by mutations in different genes. Hemophilia A and B are inherited in as X-linked recessive. The genes associated with these conditions are located on the X chromosome. In males (one X chromosome), one altered copy of the gene in each cell is adequate to cause the condition.