Human Genetic Disorders

Human Genetic Disorders

Genetic Disorders 

  • The building blocks of heredity is genes, So the defects in the genes or genome called Genetic disorders. 
  • Transfer of characters from parents to offsprings called Heredity and also known as Inheritance.
  • As a result, it passes from generation to generation.
  • Genes have all the stored data, and information, to make up DNA and proteins.
  • If any changes occur with this information is, then it leads to a genetic disorder.
  • Any kind of sudden and an inheritable change in genes is Mutation.
  • Mutant are those organisms who undergoes to mutation.
  • Any substances or the agent which has the ability to cause mutation, therefore, called Mutagen.

Genetic Disorders _ DNA

Types of Genetic Disorders
  • Genetic disorders are of two types –
  1.  Mendelian Disorders
  2. Chromosomal Disorders

Read here (Dentistry) –

Mendelian Genetic Disorders

  • An alternation or Mutation in a single gene cause this disorders.
  • Since childbirth, this conditions can found and it also predicted by the history of the family.
  • These are rare disorders, therefore, it is found in only one person among the millions of people’s.
  • Any of them can be inheritable or may not be or also sex-linked/autosomal-linked.

Here are some Mendelian Disorders –

A. Haemophilia

  • It’s a sex-linked recessive disorder, therefore, it passes generation to generation.
  • Because of the defect in the blood coagulation process, the person continues to bleed even with a small injury.
  • There are two types of Haemophilia – Haemophilia – A, and Haemophilia – B.

Genetic Disorders _ haemophilia

Haemophilia – A
  • In this disease, the person is not able to synthesize AHG (antihemophilic globulin), which is required for blood clotting, therefore a small injury can be harmful.
  • Also known as Bleeder’s disease.
  • The genes of Haemophilia is located on X- Chromosomes. i.e., X(h)
  • As we know, Female – XX, and Male – XY, So males suffer more than the females, because in males there is only one X- chromosome. Males – X(h)Y
  • Mainly, females are carriers of this disease XX(h)but she will suffer from this only in the Homozygous condition X(h)X(h) when both the chromosome consist of the hemophilia gene.
  • Queen Victoria was the carrier of hemophilia, So their male kids were suffered.
  • The defective alleles produce non-functional proteins, which also affects the process of blood coagulation.
Haemophilia – B
  • Also known as Christmas disease because of the absence of plasma thromboplastin.
  • The absence of this factor is due to the mutation.
  • Plasma thromboplastin is an important factor which is responsible for blood coagulation.
  • This factor is produced naturally in the body and it’s also known as the Christmas factor because it was discovered by Stephen Christmas.


B. Sickle-cell anemia

  • This disorder occurs due to the defect in the autosomal chromosome, therefore, it’s an autosome-linked recessive disorder.
  • In this disorder, the shape of RBCs shape turns into sickles from the disk shape.
  • This disorder can’t be cured.
  • The normal RBCs cells are of disc shape and by which they can easily pass through the veins or even in the smallest blood vessels.
  • But sickle cells are prolonged, rigid and sticky, So they can’t travel easily in the vessels by which they can’t reach the different part of the body. (blockage).
  • As a result, it can cause tissue damage, pain or it can become a clot.
  • Due to point mutation, glutamic acid got replace by valine at the sixth position of the β-Globin chain of the hemoglobin molecule.
  • The mutant hemoglobin molecule undergoes polymerization under low oxygen tension causing the change in the shape of RBC from disk to elongated.

Genetic Disorders _ sickle cell anaemia

C. Thalassemia

  • It’s also an autosomal-linked receive disorder.
  • Anemia is the main symptom of this genetic the disorder.
  • It occurs due to the deletion or mutation, as a result, defect in the synthesis of one of the globin chains of hemoglobin.
  • Due to this defect, the body is not able to produce RBCs or Haemoglobin.
  • By which, the body doesn’t have enough amount of hemoglobin to carry oxygen to the each and every organ, as a result, you will feel fatigue.
  • Thalassemia is of two type –
Alpha (α) – Thalassemia
  • In this, the production of the α – globin chain is affected. So, the production of the β-Globin chain will increase and as a result, No. of the β-Globin chain >  No. of the α-Globin chain
  • Unstable Tetramers ( 4 monomers of β-Globin chain) will form and it has abnormal oxygen dissociation curves.
  • It is controlled by the closely linked genes HBA1 and HBA2. These are two gene loci, So that means four alleles.( one gene loci = 2 allele). and they both are linked on Chromosome 16.

Beta ( β) – Thalassemia
  • In this, the production of the β-Globin chain is affected. So, the production of the α-Globin chain will increase and as a result, No. of the α-Globin chain >  No. of the β-Globin chain
  • This occurs due to the mutations in the Chromosome 11’s HBB gene. In this mutation can occur in both of the genes or maybe the mutation of one gene.
  • They don’t form Tetramers; rather, they produce damage to the cell membranes of RBCs because they get bind up with cell membranes of RBCs and membrane damage occurs.β-Thalassemia

Some Other Mendelian Genetic Disorders are:

Color blindness, Cystic Fibrosis, Phenylketonuria.

Chromosomal Genetic Disorders

  • Due to excess, abnormal arrangements or absence of one or more chromones in a cell leads to chromosomal genetic disorders.
  • During cell division, when chromatids fail to segregate properly from each other and as a result, it can be gain, loss or also abnormal arrangements in a chromosome. (Aneuploidy).
  • Some types of chromosomal disorders pass generation to generation and some may not.

Here are some Mendelian Disorders –

A. Klinefelter Syndrome

  • H. F. Klinefelter described this syndrome, in 1942.
  • Karyotype of this syndrome is (44A+XXY). It occurs in Males.
Klinefelter symptoms are:
  •  The hair on their face and body is found to be similar to women.
  •  The testis is small in size and secondary sexual symptoms are similar to women because of one extra X chromosome.
  •  Breast size is large, as a result, of one extra X chromosome.
  • The male suffering from this syndrome is sterile in a sexual manner due to the no. of chromosomes.
  • Mental retardation because of the disturbance of chromosomes.
  • Barr bodies are found in their cells, which can be one or more than one.


Klinefelter Syndrome

B. Down’s Syndrome

  • John Langdon Down first described Down syndrome, in 1866.
  • Trisomy of chromosome 21, is the reason for this disorder.
  • karyotype is “47, XY, +21
  • There are two chromatids present in a single chromosome but due to abnormalities an addition of a single chromatid occurs, as a result, it becomes Trisomy.
Down’s Syndrome symptoms are:
  • The affected person has a short-statured with small round head.
  • They have the partially open mouth and also furrowed tongue.
  • Slow mental development or Mental retardation.
  • They have a broad palm with characteristic palm crease.

Down’s Syndrome

. Turner’s Syndrome

  • Dr. Henry Turner was the first who discovered this syndrome, in 1938.
  • This syndrome occurs due to the absence of one of the X-Chromosome.
  • Their karyotype is 45+XO.
  • Due to abnormalities, there is a loss of one X chromosome.
  • It occurs in females.
Turner’s syndrome symptoms:
  • Females are sterile and also with rudimentary ovaries.
  • Their neck is of webbed type.
  • They don’t have fully developed breasts and their thorax is of shield-shaped.
  • They have short stature, puffy fingers, and small uterus.
  • Menstrual cycles are absent.

Turner’s Syndrome


1 thought on “Human Genetic Disorders”

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