Pleiotropy is a condition in which single gene affects many characters or single gene affects many phenotypes.

  • It occurs due to inter-relationship between metabolic pathways that contribute to the formation of the different phenotype.
  • Effect of the gene is more evident in one trait and less evident in other traits.


Gene for Phenylketonuria: 

  • Causes mental retardation and reduces skin and hair pigment.
  • It is an autosomal recessive metabolic disorder. Gene present on chromosome 12.
  • The gene in homozygous condition lacks Phenylalanine hydrolase enzyme, which converts Phenylalanine to Tyrosine.
  • Phenylalanine starts accumulating in blood, where it changes into Phenylpyruvic acid which is toxic to the Central Nervous System, damages the brain and causes mental retardation.
  • Melanin, the pigment is formed from Tyrosine. As Tyrosine is not formed there is a reduction in skin & hair pigment.


Gene for Sickle cell anaemia:

  • Occurs due to an autosomal recessive gene.
  • Gene in homozygous condition alters the Haemoglobin, it forms Sickle cell haemoglobin HbS.
  • It makes RBC sickle shaped, rigid and short lived. Due to which the person becomes anaemic, oxygen carrying capacity decreases and clogging of arteries occurs.
  • Gene in heterozygous condition is codominant.



Gene for starch synthesis in Pea.

BB, dominant gene in homozygous condition:

  • More effective in starch synthesis.
  • Starch grains are of larger size.
  • Seeds are round.

bb, recessive gene in homozygous condition:

  • Less effective in starch synthesis.
  • Starch grains are of smaller size.
  • Seeds are wrinkled.

Bb, gene in heterozygous condition:

  • More effective in starch synthesis.
  • Seeds are round.
  • Starch grains are of intermediate size as the gene shows incomplete dominance.


Gene for Marfan Syndrome:

  • Occurs due to an autosomal dominant gene.
  • It is a genetic disorder of connective tissue.
  • It is characterized by long limbs, hypermobility of joints, lens dislocation, and are susceptible to cardiac diseases.



Gene for white eye color in Drosophila:

  • It occurs due to a recessive gene present on the X chromosome.
  • It also causes depigmentation in many parts of the body.


ALSO WATCH: Pleiotropy


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