Unformatted text preview: le and Tatum's notion that our morphological
phenotype is the result of our biochemical phenotype (page 124 in the text).
In normal patients, homogentisic (which does not turn black in air) is converted to
maleylacetoacetate by the pathway shown above.
Noting that normal (homozygous wild type; AA) and carriers of the disease
(heterozygotes; Aa) had the same phenotype, (i.e., normal urine), Garrod
proposed that AKU was due to the complete absence of the Hgo gene in
homozygous recessive individuals (aa). Heterozygous individuals expressed
enough of the enzyme from the one normal allele to convert homogentisic acid to
02/12/14 BIS101001, Spring 2013—Genes and Gene Expression, R.L. Rodriguez ©2013
BIS101001, Spring 2013—Genes and Gene Expression, R.L. Rodriguez 10 The alkaptonuria gene (HGO) and its mutations
In 1996, researchers cloned a human gene encoding the enzyme homogentisate 1,2
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