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Ch. 16 - Genomics: Genetics from a Whole-Genome Perspective
All textbooksSanders 3rd EditionCh. 16 - Genomics: Genetics from a Whole-Genome PerspectiveProblem 16
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Chapter 16, Problem 16

Consider the phylogenetic trees below pertaining to three related species (A, B, C) that share a common ancestor (last common ancestor, or LCA). The lineage leading to species A diverges before the divergence of species B and C.

For gene X, no gene duplications have occurred in any lineage, and each gene X is derived from the ancestral gene X via speciation events. Are genes AX, BX, and CX orthologous, paralogous, or homologous? <>

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span>Understand the definitions: Orthologous genes are genes in different species that evolved from a common ancestral gene by speciation. Paralogous genes are genes related by duplication within a genome. Homologous genes are genes that share a common ancestry, which includes both orthologs and paralogs.</span
span>Identify the type of evolutionary event: The problem states that no gene duplications have occurred, and each gene X is derived from the ancestral gene X via speciation events.</span
span>Determine the relationship between the genes: Since the genes AX, BX, and CX are derived from the ancestral gene X through speciation events, they are orthologous.</span
span>Consider the phylogenetic tree: The lineage leading to species A diverges before the divergence of species B and C, but this does not affect the orthologous relationship as all genes are derived from the same ancestral gene through speciation.</span
span>Conclude based on definitions: Since the genes are derived from a common ancestor through speciation without duplication, AX, BX, and CX are orthologous genes.</span

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Orthologous Genes

Orthologous genes are genes in different species that evolved from a common ancestral gene through speciation. They typically retain the same function across species. In the context of the question, genes AX, BX, and CX are orthologous because they originated from the same ancestral gene X after the divergence of species A, B, and C.
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Paralogous Genes

Paralogous genes are genes that arise from a duplication event within a genome, leading to multiple copies that may evolve new functions. Since the question specifies that no gene duplications have occurred in any lineage, the genes in question cannot be classified as paralogous.
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Homologous Genes

Homologous genes refer to genes that share a common ancestry, which includes both orthologs and paralogs. In this case, while AX, BX, and CX are homologous because they derive from the same ancestral gene X, they are specifically orthologous due to their evolutionary relationship through speciation rather than duplication.
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Textbook Question
When the S. cerevisiae genome was sequenced and surveyed for possible genes, only about 40% of those genes had been previously identified in forward genetic screens. This left about 60% of predicted genes with no known function, leading some to dub the genes fun (function unknown) genes. As an approach to understanding the function of a certain fun gene, you wish to create a loss-of-function allele. How will you accomplish this?
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Textbook Question
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Textbook Question

Consider the phylogenetic trees below pertaining to three related species (A, B, C) that share a common ancestor (last common ancestor, or LCA). The lineage leading to species A diverges before the divergence of species B and C.

For gene Y, a gene duplication occurred in the lineage leading to A after it diverged from that, leading to B and C. Are genes AY1 and AY2 orthologous or paralogous? Are genes AY1 and BY orthologous or paralogous? Are genes BY and CY orthologous or paralogous? <>

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Textbook Question

Consider the phylogenetic trees below pertaining to three related species (A, B, C) that share a common ancestor (last common ancestor, or LCA). The lineage leading to species A diverges before the divergence of species B and C.

For gene Z, gene duplications have occurred in all species. Define orthology and paralogy relationships for the different Z genes. <>

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