Hemophilia
Hemophilia is an X-linked recessive disorder as the gene that encodes for clotting factor proteins is located on the X-chromosome.
Cause: It is caused due to mutation in one of the genes that are responsible for providing instructions to make the clotting factor proteins that are needed to form a blood clot. Thus, a mutation in this gene can retard the ability of a person to clot the blood due to a lack of clotting factors.
-Thalassemia
Thalassemia is an autosome-linked recessive blood disease.
Cause: It is caused due to either abnormal or lack of hemoglobin in red blood cells. It is due to the mutation or deletion that results in the reduced rate of synthesis of one of the globin chains of hemoglobin.
Both hemophilia and thalassemia are inherited genetic disorders but these diseases differ in some aspects which are listed below:
| Hemophilia | Thalassemia |
| X-linked recessive disorder. | Autosome-linked recessive disorder. |
| Clotting factors are lacking. | Hemoglobin is lacking. |
| Blood clotting is affected. | Anemia is the characteristic of this disease. |
Both hemophilia and thalassemia being inherited blood diseases differ in their root cause i.e., hemophilia is caused by a lack of clotting factor proteins while thalassemia is caused by lack of hemoglobin. Hemophilia mostly affects the male population while thalassemia affects both the populations i.e., male and female.
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Question: From NCERT NEET [Difficult level:Easy] NEET - 2016
Pick out the correct statements.
I. Haemophilia is a sex-linked recessive disease
II. Down's syndrome is due to aneuploidy.
III. Phenylketonuria is an autosomal recessive gene disorder
IV. Sickle cell anaemia is an x - linked recessive gene disorder
(1) II and IV are correct
(2) I, III and IV are correct
(3) I, II and III are correct
(4) I and IV are correct
Answer
(3) I, II and III are correct
Colour Blidness :
either red or green cone of eye resulting in failure to discriminate between
red and green colour. This defect is due to mutation in certain genes
present in the X chromosome. It occurs in about 8 per cent of males and
only about 0.4 per cent of females. This is because the genes that lead to
red-green colour blindness are on the X chromosome. Males have only
one X chromosome and females have two. The son of a woman
not herself colour blind because the gene is recessive. That means that its
effect is suppressed by her matching dominant normal gene. A daughter
will not normally be colour blind, unless her mother is a carrier and her
father is colour blind.
Haemophilia :
transmission from unaffected carrier female to some of the male progeny
has been widely studied. In this disease, a single protein that is a part of
the cascade of proteins involved in the clotting of blood is affected. Due to
this, in an affected individual a simple cut will result in non-stop bleeding.
The heterozygous female (carrier) for haemophilia may transmit the disease
to sons. The possibility of a female becoming a haemophilic is extremely
rare because mother of such a female has to be at least carrier and the
father should be haemophilic (unviable in the later stage of life). The family
pedigree of Queen Victoria shows a number of haemophilic descendents
as she was a carrier of the disease.
Sickle-cell anaemia :
be transmitted from parents to the offspring when both the partners are
carrier for the gene (or heterozygous). The disease is controlled by a single
pair of allele, HbA and HbS. Out of the three possible genotypes only
homozygous individuals for HbS (HbSHbS) show the diseased phenotype.
Heterozygous (HbAHbS) individuals appear apparently unaffected but they
are carrier of the disease as there is 50 per cent probability of transmission
of the mutant gene to the progeny, thus exhibiting sickle-cell trait
(Figure 5.15). The defect is caused by the substitution of Glutamic acid (Glu) by Valine (Val) at the sixth position of the beta globin chain of the
haemoglobin molecule. The substitution of amino acid in the globin
protein results due to the single base substitution at the sixth 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 RBC from biconcave disc to elongated sickle like
structure (Figure 5.15).
Phenylketonuria :
the autosomal recessive trait. The affected individual lacks an enzyme
that converts the amino acid phenylalanine into tyrosine. As a result of
this phenylalanine is accumulated and converted into phenylpyruvic acid
and other derivatives. Accumulation of these in brain results in mental
retardation. These are also excreted through urine because of its poor
absorption by kidney.
Thalassemia :
transmitted from parents to the offspring when both the partners are
unaffected carrier for the gene (or heterozygous). The defect could be due
to either mutation or deletion which ultimately results in reduced rate of
synthesis of one of the globin chains (a and b chains) that make up
haemoglobin. This causes the formation of abnormal haemoglobin
molecules resulting into anaemia which is characteristic of the disease.
Thalassemia can be classified according to which chain of the haemoglobin
molecule is affected. In a Thalassemia, production of a globin chain is
affected while in b Thalassemia, production of b globin chain is affected.
a Thalassemia is controlled by two closely linked genes HBA1 and HBA2
on chromosome 16 of each parent and it is observed due to mutation or
deletion of one or more of the four genes. The more genes affected, the
less alpha globin molecules produced. While b Thalassemia is controlled
by a single gene HBB on chromosome 11 of each parent and occurs due
to mutation of one or both the genes. Thalassemia differs from sickle-cell
anaemia in that the former is a quantitative problem of synthesising too
few globin molecules while the latter is a qualitative problem of
synthesising an incorrectly functioning globin.
