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free120/Block 2/Question#31 (reveal difficulty score)
A 10-year-old girl is brought to the office ...
It is a polymorphism 🔍 / 📺 / 🌳

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submitted by sugaplum(469),
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ceIsan eaynno else wsa nhgikint eth emas:
I asw kcstu weenetb isht dan aanrtvi fo nonwnku .ciginisecanf e,rvoHwe tvniaar of nnonwku iicifenacsng is a eeencqus otn a ngisel tcdioelneu

nbme4unme  Tkahn uyo for lgain,eipnx I esedelct hte wonnnku cenisniifagc srnwea as !llwe +5  
dhkahat  llo ckuf itsh estt +19  
chaosawaits  eBcaseu kgoinwn sith lwli eeyntfidli aekm em a etebrt tdcroo /s +1  

submitted by bwdc(675),
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A ngeietc tiavnirao ni a ruaitrpalc tecuedoiln is by nfedinoiti a ypphmoor.lmis oteN thta eth eniuotsq sfleaycpilci ttesas ahtt teh tioprne nesimra hnundg.eac

submitted by melchior(79),
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A ondn-geilucelsiet iolymporsmhp is a snlige icnteudole stsibituuton atth si epnrest ni ta tleas 1% fo het opituopanl ni( stih sqnoite,u it si .%5.7) This sfit eht nteifdniio.

mI' ont user woh ot eurl uto vantiar fo onwunnk esiicanc.ginf I gsues nesci ew nwnko atht eht ipentro si dgnhca,enu ew nca asy thta it is ont icifsginnat a(dn oretrhfee eht icnfsneacigi is not knwn.onu)

submitted by drdoom(1165),

Mom and her daughter have the same sequence of FBN1. What is special is that compared to a “normal” (wild-type) FBN1, mom and daughter have one little tiny mutation in their sequence: a single nucleotide (A,T,G,C) that is different than most other folks.

(Interestingly, this nucleotide difference does not alter the amino acid encoded by this part of the gene; that makes Choice D (change the folding of the protein) and Choice E (truncated protein) very unlikely.)

Back to our question. Even though mom and daughter have the same mutation, mom shows no signs of Marfan syndrome; this eliminates Choice A (disease-causing mutation in the patient and her mother).

You might think this is an example of variable expressivity (not an option but a good guess), and it might be.

In the stem they say:

The same nucleotide change is found in 15 of 200 individuals without Marfan syndrome.

Interesting! This means that in a “normal” sample of people (who have no signs of Marfan), 15 out of 200 still have this mutation.

(They don't say anything about how many Marfan people have the mutation but we don't need that information to answer the question.)

When a gene can be found in multiple “versions”, we call the gene polymorphic (literally, many-shapes or many-forms).

So the best response is Choice B (polymorphism).

submitted by meryen13(44),
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iegcnte lompypimhrso emnas htat tereh aer deiretnff ellaels ralnetetavi( morf of a egen taht aesris yb manutti)o fo het eams neeg ni eth tlpaonpoi.u thta si cxytlea htwa shit iseutonq wsa angnwnlioxiep . nqesecue tnaivar :sneam A cnqesee“u tn”ravai is a srtauegor metr ecvirong nya unnnteiltiaon naoim aidc tistonsbistuu, oin,omssis ro nniisserot dgiurn rnpetio yhisosst.eibn i/1k.0o22o0./pd.1.00h1s0t1sb5gpusaab/t1/-22:rhs/c10c/b-

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