You identify a gene that controls fin size in zebrafish and after examining many

Question

You identify a gene that controls fin size in zebrafish and after examining many fish you realize that in the population only two alleles exist for this gene. One allele is wild type leading to normal fins, and the other allele leads to small fins. Interestingly, only homozygous dominant individuals have a normal fin size, and all other individuals have small fins. What is the most likely explanation for the single-gene interaction of the fin alleles?

a. haplosufficient

b. complete dominance

c. codominant

d. haploinsufficient

e. recessive lethal alleles

Explanation / Answer

Answer: (d) haploinsufficient

Explanation:

Haploinsufficiency is a mechanism of action to explain a phenotype when a diploid organism has lost one copy of a gene and is left with a single functional copy of that gene. Haploinsufficiency is often caused by a loss-of-function mutation, in which having only one copy of the wild-type allele is not sufficient to produce the wild-type phenotype.

It occurs when an organism has a single functional copy of a gene, and that single copy does not produce enough product to display the wild type's phenotypic characteristics. The general assumption is that the single remaining functional copy of the gene cannot provide sufficient gene product (typically a protein) to preserve the wild-type phenotype leading to an altered or even diseased state.

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