Question

Some mutations have a cis-effect, whereas others have a transeffect. Explain the molecular differences between cis- and transmutations. Which type of mutation (cis or trans) can be complemented in a merozygote experiment?

Short answer

A cis mutation affects the function of genes on the same DNA molecule where the mutation has occurred, whereas a trans mutation can affect the function of genes on different DNA molecules. In merozygote experiments, only trans mutations can be complemented because a wild-type allele on one chromosome can provide a normal gene product that can be used by the other chromosomes.

Step-by-step solution

Understanding Cis and Trans mutations

Cis and trans are two terms used to explain genetic linkage and gene expression. A cis-mutation or a cis-effect means that the mutation and the gene where it impacts are on the same allele (same DNA molecule). On the other hand, trans-mutations or trans-effects mean that the mutation and the gene it impacts are on different alleles (different DNA molecules). Cis-acting mutation affects only the individual gene or sequence where the mutation has occurred, while a trans-acting mutation can affect the function of genes that are distant from the location of the mutation.

Merozygote experiment

A merozygote experiment involves creating a partial diploid condition in a haploid bacteria, it is often used in bacterial genetics to determine whether a particular mutation affects a gene product or not. It is a type of genetic complementation test.

Determining which mutation can be complemented

In merozygote experiments, only trans-acting mutations can be complemented. This is because a wild-type allele on one chromosome can produce a normal gene product that can be used by other chromosomes. In other words, the effect of trans-acting mutation can be 'trans'ferred or compensated by a normal gene present on the other allele. Conversely, cis-acting mutations cannot be complemented because the mutated gene or sequence impacts only the activity on the same DNA molecule where the mutation has occurred and not on the other allele.