Achondroplasia (a form of dwarfism) is caused by a mutation in the fibroblast gr

Question

Achondroplasia (a form of dwarfism) is caused by a mutation in the fibroblast growth factor receptor 3 (FGFR3) gene. Possessing just one copy of the mutated receptor gene leads to severely shortened bones. Individuals with achondroplasia always have one mutant allele at this locus and one normal allele - no individuals with two copies of the mutant allele have ever been observed. What does this suggest about the genetic basis of achondroplasia?

a. The mutant allele is recessive for both achondroplasia and lethality.

b. The mutant allele is recessive for achondroplasia but also a dominant lethal allele.

c. The mutant allele is dominant for achondroplasia but also a recessive lethal allele.

d. The mutant allele is dominant for both achondroplasia and lethality.

e. The mutant allele and the recessive allele must be on different chromosomes.

Explanation / Answer

The answer is -c) The mutant allele is dominant for achondroplasia but also a recessive lethal allele.

Achondroplasia expresses in presence of single mutant allele. So it is certainly a dominant trait.

And two mutant is not observed in nature. That means 2 mutant allele results in complete lethality.

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