Question 1

What is gene duplication and how does it occur in genomes?

Accepted Answer

Gene duplication is a process where a DNA region coding for a gene duplicates, creating additional copies within the same genome. Duplication can arise through unequal crossing over during meiosis, replication slippage where DNA polymerase dissociates and realigns incorrectly, or retrotransposition where mRNA is reverse transcribed into DNA copies called retrogenes that reinsert into the genome.

Question 2

What are paralogs and how do they relate to gene families?

Accepted Answer

Paralogs are duplicated copies of genes with similar sequences and functions. When paralogs share enough similarity, they form a gene family. Gene families are widespread across species; for example, the trypsin gene family in D. melanogaster has over 111 members, while the olfactory receptor gene family in mammals contains around 1000 member genes.

Question 3

How does sub-functionalization differ from neo-functionalization after gene duplication?

Accepted Answer

Sub-functionalization occurs when both paralogs acquire mutations in different protein domains, partitioning the original gene function between them while their protein products complement each other. Neo-functionalization happens when one paralog acquires novel mutations leading to a new gene function, while the other retains the original function, as seen with fetal β-globin evolution.

Question 4

What is a pseudogene and how does it form from gene duplication?

Accepted Answer

A pseudogene is a nonfunctional copy of a gene that forms when one paralog acquires deleterious mutations after duplication. Pseudogenes commonly arise from retrotransposition, where inserted retrogenes lack promoters and regulatory elements necessary for transcription, causing them to lose function over time.

Question 5

How did hemoglobin evolution demonstrate sub-functionalization in vertebrates?

Accepted Answer

In primitive fish and marine animals, a single globin gene encoded oxygen-carrying proteins. During evolution, the globin gene duplicated and sub-functionalized into α-globin and β-globin genes. These proteins associate to form hemoglobin with four subunits found in modern vertebrates, with each protein complementing the other to maintain oxygen transport function.

Question 6

What role did gene duplication play in the evolution of primate color vision?

Accepted Answer

Early primates had dichromatic vision from Blue and Green opsin genes. The Green opsin gene later duplicated and neo-functionalized into a novel Red opsin gene. Species evolving after this duplication, including old world monkeys, apes, and humans, gained three opsin genes enabling tricolor vision.

Question 7

What is whole-genome duplication and how does it differ from single gene duplication?

Accepted Answer

Whole-genome duplication occurs when entire chromosomes or genomes duplicate, often through chromosome segregation failures during meiosis. Unlike single gene duplication, this creates multiple copies of all genes simultaneously. For example, wheat genomes have duplicated six times, creating a hexaploid organism with multiple chromosome sets.

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