R en d er it in ac t iv e t h i s i s an o t h er ex

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Unformatted text preview: s i s an o t h er ex am p l e o f h o w c h an g in g o n e • PAO activity → loss of green color: peas become yellow • PAO gene has two alleles: wt, lof • wt/wt peas are ___________ • lof/lof peas are ___________ • wt/lof peas are ___________ based on your last answer, which is dominant? 384 THE AMERICAN BIOLOGY TEACHER VOLUME 73, NO. 7, SEPTEMBER 2011 Example 2: Loss of function mutation tyrosinase gene tyrosinase mRNA tyrosine tyrosinase protein melanin (pigment) complete absence of tyrosinase activity → complete absence of melanin → albinism (one form) Different alleles with different outcomes homozygous for active enzyme What does a heterozygous cat look like? homozygous for inactive enzyme burnerkitty.com C C C *c tyrosinase tyrosinase tyrosinase tyrosinase General rule for LOF mutations… Half the amount of wild type gene product is sufficient to give a wild type phenotype wild type allele =C mutant =c exam ple: tyrosinase [enzym e activity Genotype: CC threshold wild type phenotype albino phenotype Cc c c 1 wild type copy → enzyme activity above threshold needed for normal pigmentation, heterozygotes appear unaffected (these are carriers) Temperature-sensitive proteins Proteins unfold upon heating. increasing temperature missense...
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