Mendelian Disorders – Class 12 | Chapter – 5 | Biology Short Notes Series PDF

Mendelian Disorders: Mendelian disorders are mainly determined by alteration or mutation in the single gene. These disorders are transmitted to the offspring on the same lines as we have studied in the principle of inheritance. Most common and prevalent Mendelian disorders are Hemophilia, Cystic fibrosis, Sickle-cell anemia, Colour blindness, Phenylketonuria, Thalassemia, etc. It is evident that this X-linked recessive trait shows transmission from carrier female to male progeny.

Examples of Mendelian Disorders

Name	Genetic Trait	Cause	Effects	Inheritance pattern
Sickle cell anaemia	Autosome-linked recessive	A single point mutation in the beta-globin chain of haemoglobin	Anaemia	Offsprings may get the disease when both the parents are a carrier (heterozygote)
Thalassemia	Autosome-linked recessive	Mutation in the genes HBA1 and HBA2 present on the chromosome 16	Formation of abnormal haemoglobin molecule resulting in anaemia	Offsprings may get the disease when both the parents are a carrier (heterozygote)
Phenylketonuria	Autosome-linked recessive	Lack of an enzyme that converts phenylalanine to tyrosine	Mental retardation. Accumulation and excretion of phenylalanine and its derivatives in urine	Offsprings may get the disease when both the parents are a carrier (heterozygote)
Colour blindness	X-linked recessive	Defect in the green or red cone of the eye	Unable to discriminate between red and green colour	A daughter will be colour blind only if the father is colour blind There is a 50 percent probability of a carrier female to transfer the disease to sons
Haemophilia	X-linked recessive	Defect in one protein involved in the clotting of blood	Continuous bleeding from wounds	A daughter will be colour blind only if the father is colour blind There is a 50 percent probability of a carrier female to transfer the disease to sons

 

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By Team Learning Mantras