. The physicist Stephen Hawking, famous for his theories about black holes, has lived past the age of 70 withamyotrophic lateral sclerosis (ALS), a paralyzing neurodegenerative disease that is usually fatal at a muchyounger age. Recently, geneticists discovered that amajor cause of ALS is the unusual expansion of ahexanucleotide repeat (5′-GGGGCC-3′) that lieswithin a gene called C9ORF72, at a location outside ofthe gene’s open reading frame (ORF). A single expanded allele is sufficient to cause ALS, but the reasonthe disease allele is dominant remains unclear. Someexperimental results support the theory that the allelemakes a toxic RNA containing the expanded repeat. Ifthis theory is correct, in what ways is the mutant ALScausing allele similar to the mutant allele that causesHuntington disease? In what ways is it similar to themutant allele that causes fragile X syndrome?
. The physicist Stephen Hawking, famous for his theories about black holes, has lived past the age of 70 with
amyotrophic lateral sclerosis (ALS), a paralyzing neurodegenerative disease that is usually fatal at a much
younger age. Recently, geneticists discovered that a
major cause of ALS is the unusual expansion of a
hexanucleotide repeat (5′-GGGGCC-3′) that lies
within a gene called C9ORF72, at a location outside of
the gene’s open reading frame (ORF). A single expanded allele is sufficient to cause ALS, but the reason
the disease allele is dominant remains unclear. Some
experimental results support the theory that the allele
makes a toxic RNA containing the expanded repeat. If
this theory is correct, in what ways is the mutant ALScausing allele similar to the mutant allele that causes
Huntington disease? In what ways is it similar to the
mutant allele that causes fragile X syndrome?
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