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Author2 Posts
  #1

plz help me in solvin this ques.
An investigator is studying a large family with many members who are affected by a disorder caused by a fully penetrant autosomal dominant inherited gene mutation. A pedigree is shown. Most affected members also have a rare allele at a locus thought to be closely linked to the disease locus. A father (individual III-3) and his daughter (individual IV-3) have the disorder, but they have the wild-type allele at the linked locus. Which of the following is the most likely cause of these findings?

A
)
Insertion of a LINE sequence

B
)
Random segregation

C
)
Recombination

D
)
Single nucleotide polymorphism

E
)
Transduction


  #2

i never come to this kind of subject forums bc i dont learn much from it , but this is a good question , where is this Q from ?

ok here my reasoning , if someone else know the answer please correct me but explain the "WHY" :

1. seems to me that this investigator is doing a family base study , not a genome-wide association study. another point to noticed is the usage of word "linked"
2. in the question apparently they wanna know if we understand some basic concepts and how to put them together , concepts like:
a. fully penetrant autosomal dominant inherited gene mutation, and by 'fully' i understand 'complete" penetrance where all individuals who have the disease-causing mutation have clinical symptoms of the disease.
b. know how to read pedigree analysis.
c. this 'rare' allele , its basically saying " mutant allele" and the "wild allele" is conceptualized as a product of the standard, "normal" allele at a locus, in contrast to that produced by a non-standard, "mutant" allele.
2. the question is , what is the cause of this findings ? we ask to ourselves what finding ?.. the why most (not ALL) of them have this rare allele closely linked to disease locus , compare with this father and daughter that instead have the wild type ? or im reading the question wrong?? and therefore my analysis is also WRONG ...

> you didnt put the pedigree analysis in this post , so..this individual III-3 ,mate with who?(im not asking sex,bc the problem in question is related to autosomes). by having the pedigree analysis will help to come to a better conclusion (a mother with possible N allele ? ) ,, i know that in an autosomal dominant disease, only the gametes of the affected parent (or non-penetrant gene carrier parent) will contribute linkage information , but the unaffected non-gene carrier parent will provides genetic info that help to interpret the transmission of the disease and marker loci (for a specific type genetic analysis) to her children from the affected father.

> this LINEs ,Long Interspersed Elements ,by using reverse transcriptase make a DNA copy and then integrate it into the genome at a new site, thereby can increase genome size. this alleles in question are closely linked . so this non-LTR retrotransposon mech will not cause this findings.

> when the III-3 individual mated ,segregation and recombination happened which both occurs at random , now since both alleles are closely linked , is less likely that this sequences will recombine , this sequences will tend to stay together rather than being split apart by recombination . but by gene conversion (in genetic recombination) it would be possible for the rare allele to be changed into wild-type allele,Gene conversion of an allele bearing inherited pathogenic mutation can occasionally lead to the reversion of the disease phenotype (not seen in this case ) ,called natural gene therapy ,in theory this can occur only by different mutations in the two alleles, resulting in somatic mosaicism.

now assuming that the mother (of daughter IV-3) have both wild type alleles (a/a , letters just for this assumption) and the father (A/a) who have the dominant mutant allele (A) also have the wild type (a), (gametes A,a,a,a), after mating the dominant mutation can segregate resulting in the A/a daughter IV-3 (with the disorder and the wild type ), this can also apply to the father progenitors, so and the answer of this question will be segregation.
another mech that can explain rare allele to wild type is suppressor mutation ,but this likely occurs if the mutation was cause by a base deletion ,but is not the case.

> transduction , in here DNA is transferred from one bacterium to another by a virus. It also refers to the process where foreign DNA is introduced into another cell via a viral vector. NOT related to this case.

> SNPs ,as far as i know SNPs are evolutionarily stable—not changing much from generation to generation, also their effects depends where the sequence variation occurred ( coding ,non coding , intergenic regions) ,and they usually work with other SNPs to manifest a trait...SNPs not an option

unless there is another explanation/analysis to answer this Q ,

segregation is the best option.





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