PSET5Sa

PSET5Sa - Solution key - 2010 7.012 Problem Set 5 Question...

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1 Solution key - 2010 7.012 Problem Set 5 Question 1 A s ingle n ucleotide polymorphism (SNP) is a DNA sequence variation occurring when a single base pair in the genome differs between members of a species or paired chromosomes in an individual. By convention this base pair change is represented as one nucleotide — A, T, C, or G — of the base pair. a) Circle the correct option from the following choices. The SNPs may exist … i. only within the coding sequences of genes. ii. only within the non-coding regions of genes. iii. only in the coding and non-coding regions of the genes. iv. in the coding or non-coding regions of the genes or in the intergenic regions between the genes. b) In which region or regions ( coding sequence of the gene/ non-coding sequence of the gene/ intergenic sequence ) would you expect the SNP to be if … i. it changes the amino acid sequence of the protein which is produced? Include all the possible options . The SNP can only be in the coding sequence (i.e. exons) of the gene that codes for the amino acids of the protein. ii. it does not change the amino acid sequence of the protein which is produced? Include all the possible options and give an explanation for each selected option . The SNP may be in the coding region assuming that it creates a silent mutation that does not change the amino acid sequence of the protein. It may also be in the non-coding sequence (i.e. introns) of the genes or the intergenic regions between the genes because these segments do not code for the amino acids of the protein. c) You are studying a family with an inherited disease associated with Gene Z. You identify two SNPs that are linked to Gene Z, SNP1 is closer to Gene Z than is SNP2. Explain why you would use SNP1 and not SNP2 as a marker to follow the inheritance pattern of this disease in the family. You want to use SNP 1 as a marker because the closer the two loci are the lesser is the chance of a recombination event occurring between them. d) Below is the pedigree of a family with this disease. All the individuals that show the disease phenotype are shaded and the carriers are striped. Also listed are the alleles of a SNP (A, G, T, C) for some individuals. Note: you may assume that this SNP is tightly linked to Gene Z and may be used as a marker for the disease. Assume complete penetrance. i. What is the most likely mode of inheritance (autosomal dominant/ autosomal recessive/ X linked dominant/ X linked recessive) of this disease? X linked recessive ii. Identify the SNP that is tightly linked with the disease allele. G G,G A,G G,A G,C G,A C,A C,T G,A C,G 2 1 Please note: the two letters identify the two alleles of the SNP. For example G, C indicates that on one of the chromosomes you would find a G (a G/C base pair) and on other chromosome you would find a C (a C/G base pair).
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2 Question 1 continued iii. What is the most likely genotype at the Z locus of Individuals 1 and 2 in this pedigree? Note: Use the symbol X D , X d , D or d where appropriate. In each case, use the letter “D” to represent the allele
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PSET5Sa - Solution key - 2010 7.012 Problem Set 5 Question...

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