A gene encodes a protein that carries out two functions. The following series of

Question

A gene encodes a protein that carries out two functions. The following series of events occurs:

This gene becomes duplicated.

The duplicated genes subfunctionalize such that each paralog retains one of the two functions.

One paralog acquires an additional new function.

A speciation event occurs, and the two paralogs in one species diverge in sequence from the two paralogs in the other species. However, the genes maintain the same functions.

Discuss the functional impact of nucleotide substitutions that are likely to sweep through the population at each stage after the duplication event. Explain why certain types of mutations are likely to become fixed at each stage. What effect would these mutations have on fitness?

Explanation / Answer

Common sources of gene duplications include ectopic recombination, retrotransposition event, aneuploidy, polyploidy, and replication slippage.

Human gene function can often be carried out on other species if a homolog to a human gene can be found in the genome of that species, but only if the homolog is orthologous. If they are paralogs and resulted from a gene duplication event, their functions are likely to be too different. One or more copies of duplicated genes that constitute a gene family may be affected by insertion of transposable elements that causes significant variation between them in their sequence and finally may become responsible for divergent evolution. This may also render the chances and the rate of gene conversion between the homologs of gene duplicates due to less or no similarity in their sequences.

The mutational effects on fitness (DME)

It specifies the probability distribution of selection coefficients for spontaneous mutations of a given genome. Thus, it could be argued that the DME is highly dependent on the genotype; but all organisms are complex functional networks and have ‘learned’ to live with a flux of new mutations, such that powerful normalizing forces might cause the DMEs we can observe today to share important properties. For example, the total of fitness degrading and fitness increasing effects that get fixed might be in equilibrium such that there is no unbounded change in fitness in most populations.

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