
Concept explainers
a.
To explain: The reason for gene duplicates being so dead on arrival.
Introduction: The mechanism in which messenger RNA is reverse transcribed into DNA leading to the integration of DNA into the genome is called retrotransposition. The process results in the formation of duplicate genes which are different from the parental genome and also present on a different chromosome. Retrotransposition can result in the formation of pseudogenes.
a.

Explanation of Solution
Duplicative genes arising from retrotransposition does not have introns. However, due to the lack of introns, they can be easily distinguished from the parental genes, and they may not undergo post-transcriptional changes resulting in the death of the genes (pseudogenes). Therefore, that they are often dead on arrival.
b.
To explain: The duplicative genes obtained after unequal crossing over is more functional than gene arise by retrotransposition.
Introduction: The formation of duplicative genes can occur by unequal crossing over and through retrotransposition. Unequal crossing over results from misalignment of the chromosomes during meiosis ultimately leading to the process of recombination. Retrotransposition results in the formation of duplicate genes which are different from the parental genome and also present on a different chromosome. Unequal crossing over results in the formation of functional gene products while retrotransposition leads to the formation of pseudogenes.
b.

Explanation of Solution
The gene duplicates formed due to unequal crossing over is functional in nature as they have introns and exons. The gene duplicates are capable to undergo post-transcriptional modifications leading to the formation of functional protein. In case of retrotransposition gene duplicates does not have introns. However, due to lack of introns, they cannot undergo post-transcriptional modifications thereby resulting in nonfunctional gene product.
c.
To discuss: The ultimate fates of functional gene duplicates.
Introduction: The gene duplicates arising from different mechanisms after being fixed in a population can undergo several fates. The formation of duplicative genes can occur by unequal crossing over and through retrotransposition. The gene duplicates may lose their function due to deletion or may retain its original function.
c.

Explanation of Solution
Functional gene products arising from different mechanisms can undergo four different fates which are as follows:
- The redundancy of the gene duplicate may result in the deletion of the duplicate gene product.
- The gene duplicate may retain its original function. These duplicates are favored as they are able to retain their function due to which they can undergo the process of selection for increased gene expression.
- The duplicate gene product would evolve as the gene that is characterized by novel biological function.
- The parent gene along with duplicate gene products may subfunctionalize to perform the functions related to ancestral genes.
To determine: The most suitable fate of gene duplication.
Introduction: The gene duplicates arising from different mechanisms after being fixed in a population can undergo several fates. The formation of duplicative genes can occur by unequal crossing over and through retrotransposition. The gene duplicates may lose their function due to deletion or may retain its original function.

Explanation of Solution
The process of gene duplication resulting in retaining the original function of the gene is more likely to happen as the genes can undergo the process of selection for increased gene expression.
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Chapter 14 Solutions
Evolution
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