Question

Actice: Mutations - A -P--I--3--H--N--R--6--8- --11--11-- - ----- CGI GATTIOTITATITCATCCARAGATCTGGGC ATGACHATAGCTATCTACH --6-- -F-- - --5--5--K -3 -4--G-- ----y--5--4--1--0 -- -- SOBOTACECCO THACACOLAGACICITITCAAGACTACATTAASTCCTATTTGGAACAAGCGAC CG 3 -D-P-- -- -- - -- -- --I--K -3-wY--1-- --0-- --3--2 MES CATCH.CCTCRIGGST SELCATOGICCITGGGGCCGCGADGGLAGGCGCSGTCC CACHGCOCTOCT 3GC --3-- -- -- -- -- -- - - -- 173 W 179 AGGCT GTGAGTT AGTIGCTGIGTCGI CACAAGAGAAAGCAGCTCCTGAAGAARSCAGOGI -s--1 -1 - 6 -R- -11--1--2--3--0--I -F - 6--6--8--0--p RTCCTCATCCAGAAGAGGA TACCACAGCHET 13 -1 1 -- --3--R-- -- - BAGGATACCACAGTGTATORGAGCCWT TATAA........ -- -- -- - - -- -- - Y-- - -- -- -- -- -- -- A person known to have albinism has a homozygous 1-basepair insertion in Exon 2 of the TRY gene. This mutation results in a premature STOP codon after amino acid residue #298. i What does "homozygous" mean in this problem? Having two identical alleles of a particular gene How many copies of the TYR gene are affected in this scenario? iii. How does this mutation result in a premature STOP codon? b. A person known to have albinism has a heterozygous mutation that results in pro81-lue substitution that interferes with normal folding of the tyrosinase protein. i. What does "heterozygous" mean in this problem? . How many copies of the TYR gene are affected in this scenario? iii. Do you think this person has a complete or partial lack of pigment? Explain your reasoning. tr = y = k, pro = P, led = [. C. Do people with albinism have the TYR gene? Do people without albinism have the TYR gene?

Answer 1

A(i)homozygous- means identical alleles of a gene, this question tell us that there is a insertion of homozygous base pair in the exon2(coding portion as compared to intron which are spliced out in mRNA processisng)

(ii)all the copies of TYR gene are affected as this is a genetic change

(iii)stop codon are the nucleotide triplets in the mRNA that signals termination of translation of mRNA into proteins.example-UAG,UAA,UGA

without insertion mRNA- AUG-GCC-GGG-AAU-GAG

with insertion of A    - AUG-GCC-GGG-AAA-UGA-G

with insertion of a nucleotide or basepair the reading frame shifts leading to frame shift mutation, which might code for a stop codon which was not there in intital mRNA. this will lead to a shorter protein size as comapred to wild type mRNA

B(i) in this heterozygous means two different alleles are present, one is a functional copy and other is nonfunctional

(ii)one copy is affected

(iii)persond should have partial lack of pigmentation as one functional copy of the gene will produce tyrosinase which is functional and help in production of melanin (responisble for pigment formation)

C. all the people have TYR gene which codes for tyrosinase however in the people with albinism the activity of the enzyme is reduced if they have only one functional copy(heterozygous) due to mutations or complete lack of activtiy in homozygous situation.

III.TYR(fs)-variable length protein, if frame shift leads to stop codon then there will be premature termination

mRNA and gene length will be almost similar as compared to WT

TYR(spliced)similar gene length as to WT

matured mRNA will be shorter then WT

incomplete will be coded by the TYR(spliced)