Mutations of regulatory elements of developmental genes may have either dominant or recessive effects. If a mutation deletes a silencer upstream of a HOX gene, which do you expect?
A) a dominant trans effect on both alleles of the HOX gene
B) a dominant effect in which cis HOX gene activity is up- regulated
C) a dominant effect which down- regulates HOX gene activity
D) a recessive effect in which cis HOX genes are down- regulated
E) a recessive effect in which cis HOX genes are up- regulated

Question

Quizplus · Accepted Answer

Deleting a silencer upstream of a HOX gene removes a regulatory element that normally suppresses gene expression. Therefore, the activity of the HOX gene located on the same chromosome (in cis) would be up-regulated. This effect would be dominant because the increased expression from one allele would be sufficient to alter the phenotype, regardless of the state of the other allele.

Mutations of Regulatory Elements of Developmental Genes May Have Either