Biology Inheritance / Variation & Genetics SZABMU 2023
PMDC Verified Question 39 of 94
Which of the following example of human inheritance is explained by multiple alleles on an autosomal chromosome?
A
The ABO blood group system
B
Cystic fibrosis
C
Down's syndrome
D
Haemophilia
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option A: The ABO blood group system
Concept:

Multiple allelism describes a gene with three or more variants in a population.

Solution:

  • The ABO blood group system is controlled by three distinct alleles (\(I^A\), \(I^B\), \(i\)).
  • These alleles are located on Gene I, which sits on Chromosome 9.
  • Since Chromosome 9 is an autosome (not a sex chromosome), ABO inheritance is correctly categorized as multiple alleles on an autosomal chromosome.


Why other options are incorrect:

  • Cystic fibrosis: An autosomal recessive trait, typically viewed through standard two-allele Mendelian genetics.
  • Down's syndrome: A chromosomal abnormality (Trisomy 21), not a multiple allelic trait.
  • Haemophilia: An X-linked (sex chromosome) recessive trait.

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