Topics to be covered this video :-

Mendelian disorders
i. Colourblindness
ii. Haemophillia
iii. Sickle cell anemia
iv. Phenylketonuria
v. Thalassemia

Chromosomal disorder
i. Down syndrome
ii. Klinefelter’s syndrome
iii. Turner’s syndrome

Mendelian disorder

• Mutation in single gene.
• They are transferred to offsprings as per Mendelin principle of inheritance.
  i. Colourblindness
  ii. Haemophillia
  iii. Sickle cell anemia
  iv. Phenylketonuria
  v. Thalassemia

Colour blindness

• Colour blindness is a recessive sex linked trait in which eye fails to distinguish red and green colours.
• The normal gene and its recessive allele carried by X- chromosomes.
• In females colour blindness appears only when both the sex chromosomes carry the recessive gene . (XX)
• The females have normal vision but function as carrier if fa single recessive genes for colour blindness is present(XX)
• human males the defect appear in the presence of a single recessive gene (XY) .

Haemophilia

• It is X-linked recessive trait.
• Due to absence of defective form of blood clotting factor (protein) exposed blood of affected individuals fails to coagulate.
• The possibility of a female becoming a haemophillic is extremely rare because mother of such a female has to be atleast carriers and the father should be haemophilic.
• Haemophilic female dies before birth.
• The family of queen Victoria shows a number of haemophilic descendent as she was a carrier of the disease.
• The person suffering from this disease cannot synthesize a normal blood protein called antihaemophillic globulin (AHG) required for normal blood clotting.
• Therefore even a very small cut may lead to continuous bleeding for a long time.
• This gene is located on X- chromosomes and is recessive.

SICKLE CELL ANEMIA

• It is an autosomal recessive disease therefore it can be transmitted from parents to the offspring when both male and female individuals are carrier (heterozygous) for the gene.
• The disease is controlled by a single pair of allele, Hb and Hb.
• Thus three genotypes are possible in population
• Hb Hb (normal, homozygous ) A
• Hb (normal, carrier)
• Hb Hb (Diseased die before attains maturity)
• Heterozygous individual appear unaffected but they a are carrier of the disease as there is 50% probability of transmission of mutant gene to progeny, thus exhibit sickle cell trait.
• The disease is caused by mutation of the gene controlling ẞ-globin chain of haemoglobin.
• It replaces glutamic acid (GLU) present at 6th position of ẞ- chain by amino acid valine (VAL).
• It cause change in shape of RBC from biconcave shape to elongated sickle cell structure.

Phenylketonuria

• It is autosomal recessive trait.
• The affected individual lacks a liver enzyme called phenylalanine hydroxylase that converts aminoacid phenylalanine into tyrosine.
• As a result of this phenylpyruvic acid and other derivatives.
• Accmulation of these in brain results in mental retardation.

Thalassemia ( blood disorder)

• It is a autosomal recessive trait.
• It is responsible for lysis of cell and in anaemia.