Question

(A)Why are thalassemia and haemophilia categorized as mendelian disorders?
Write the symptoms of these diseases. Explain the pattern of inheritance in humans.
 (B)Write the genotype of normal parents producing haemophilic sons.

Answer 1

Hint: Thalassemia is a hereditary blood condition that affects haemoglobin development. Haemophilia is an inherited genetic disorder that hampers a person's ability to clot blood due to a lack of clotting factors. Hemophilia and thalassemia are both human blood-related disorders.

Complete answer:
Thalassemia and Haemophilia are known as Mendelian disorders since they occur in a single gene by mutation. Their inheritance mode follows the Mendelian genetic theory. Mendelian disorders may be
A. Autosomal dominant(dystrophy of muscle)
B. Autosomal Recessive(thalassemia)
C. Sex linked (Haemophilia)

Thalassemia symptoms:
1. Minor thalassemia results only in moderate anaemia, marked by low levels of haemoglobin.
2. Thalassemia major is referred to as Cooley's anaemia. In this condition, the children affected look normal but experience extreme anaemia, skeletal deformities, jaundice, weakness, etc as they reach 6 to 9 months.

Hemophilia symptoms
Individuals with this condition do not establish a suitable system for blood clotting.
Also from a very simple cut, which can lead to death, a haemophilic patient experiences non stop bleeding.

Pattern Inheritance of Thalassemia:
Pair of allele \[H{{b}^{A}}\] and \[H{{b}^{A}}\] controls the expression of this disease
Conditions for thalassemia
1.Normal -\[H{{b}^{A}}\] and \[H{{b}^{A}}\]
2.Carrier-\[H{{b}^{A}}\] and \[H{{b}^{T}}\]
3.Diseased\[H{{b}^{T}}\] and \[H{{b}^{T}}\]

Let us assume both father and mother are carriers (HbA and HbT)of beta thalassemia.

Parents		\[H{{b}^{A}}\]\[H{{b}^{T}}\]father	x	\[H{{b}^{A}}\]\[H{{b}^{T}}\](Mother)
Offspring	\[H{{b}^{A}}\]\[H{{b}^{A}}\]Normal child	\[H{{b}^{A}}\]\[H{{b}^{T}}\]Carrier child with thalassemia trait	\[H{{b}^{A}}\]\[H{{b}^{T}}\]Carrier child with thalassemia trait	\[H{{b}^{T}}\]\[H{{b}^{T}}\]Carrier child with severe thalassemia trait

Pattern Inheritance of Haemophilia:
Haemophilia is a X-linked hereditary condition. Relative to females, males are more likely to be affected because females have XX chromosomes and males have only one X chromosome with Y chromosome. Thus, for a female to be affected by haemophilia, she must have the mutant gene on both X chromosomes while males may be affected if they carry it on one chromosome.
Conditions:
1.Normal-XY,XX
2.Carrier-\[{{X}^{h}}X\]
3.Haemophilic-\[{{X}^{h}}X\] , \[{{X}^{h}}{{X}^{h}}\]

Parents		XY(Male)	x	\[{{X}^{h}}X\](Female)
Offspring	\[{{X}^{h}}X\]Carrier female	XXNormal female	\[{{X}^{h}}Y\]Haemophilic male	XYNormal Male

(b) The genotype of the normal parents having a haemophilic son are:
Mother: \[{{X}^{h}}X\] (normal) ;
Father: XY (normal)
Son: \[{{X}^{h}}Y\] (haemophilic)

Note: However unlike haemophilia, the abnormal thalassemia alleles in both males and females show themselves only when they are in a homozygous state. The recessive heterozygous remain unnoticed, but function as heterozygous carriers.