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“Six-rowed barley originated from a mutation in a……… homeobox gene”

“Six-rowed barley originated from a mutation in a……… homeobox gene” Two-rowed is ancestral (wild type) Homeobox genes are transcription factors – they encode proteins that bind to other genes and thus regulate the expression of other genes The “virtual” model -

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“Six-rowed barley originated from a mutation in a……… homeobox gene”

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  1. “Six-rowed barley originated from a mutation in a……… • homeobox gene” • Two-rowed is ancestral (wild type) • Homeobox genes are transcription factors – they encode proteins that bind to other genes and thus regulate the expression of other genes • The “virtual” model - • In a two-row, the product of Vrs1 binds to another (unknown) gene (or genes) that determine the fertility of lateral florets. For convenience, the unknown gene will be abbreviated as Lat • When there is no expression of Lat, lateral florets are sterile and thus the inflorescence has two rows of lateral florets

  2. X • Transcription of Vrs1 • Translation of Vrs1 • Binding of Vrs1 to Lat • No expression of Lat =2-row Vrs1 Lat

  3. X X No transcription of vrs1 (or) No translation of vrs1 No binding of vrs1 to Lat Lat expresses and lateral florets are fertile = 6-row vrs1 Lat

  4. What happened to Vrs1 to make it vrs1? • There are several scenarios that can lead to this loss-of-function. • Complete deletion of the gene ( - transcription, - translation = no protein) • Deletions of (or insertions into) key regions of the gene leading to - transcription and/or + transcription but – translation, or incorrect translation = no protein • Nucleotide changes leading to (+ transcription but incorrect translation = non-functional protein

  5. How many alleles are possible at a locus? • Only two per diploid individual, but many are possible in a population of individuals • New alleles arise through mutation • Some mutations have no discernible effect on phenotype • Different mutations in the same gene may lead to the same or different phenotypes

  6. All this happened to VRS1 in the past 10,000 years!

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