Consider the triangular diagram shown in Fig. 21.15 on p. 708 a. What feature of
ID: 99206 • Letter: C
Question
Consider the triangular diagram shown in Fig. 21.15 on p. 708 a. What feature of the genome is likely to be located between the two LD blocks that allows scientists to visualize them as separate blocks? b. Even though the figure analyzes nine different SNPs, genotyping just two of these SNPs would allow you to predict the genotype of almost everyone in the population. Explain why this limited genotyping has predictive value. c. When obtaining the data allowing construction of triangular diagrams, have researchers typically genotyped common SNPs or rare SNPs? Explain. d. Considering your answer to part (b), why are human population geneticists interested in obtaining complete whole-genome sequences, as opposed to genotyping only the small subset of predictive SNPs? Figure 21.15 Clusters ("blocks") of LD found among SNPs across the human genome. A segment of the genome Is expanded in the second row as a block of sequence with the locations of nine SNPs indicated. At the bottom is a "triangle diagram" with block color indicating the strength of the statistical correlation (LD) for pairwise comparisons of the indicated SNPs (progressively weaker correlations are in dark brown, light brown, blue, and white, respectively).Explanation / Answer
LD blocks are linkage disequilibrium blocks present in a chromosome.
It is defined as an event in genetics when some alleles tend to appear together and they don't recombine during meosis.
Eg. If a father has a and b allele on a chromosome. And mother has A and B allele on the same chromosome.
Then in case of linkage disequilibrium, child would either have alleles a and b inherited from father.. Or A and B allele inherited from mother. And no chances of formation of a mixed phenotype.
SNP is single nucleotide polymorphism.
These are sequences on the chromosome with change in only a single nucleotide base pair.
The region on the chromosome in which SNP loci that are inherited together is known as haplotype.
a.) The two LD blocks a are separated by recombination hot spots on the chromosome. These are the places where chance of recombination are very high as compared to LD blocks.
b.) Genotyping just a few SNPs would tell us where they are inherited from ie. from mother or father. and also as recombination is very rare within these blocks. So, they would persist for many years in many people of a population.
c.) Researchers would have used common SNPs:-
to identify the genes responsible for diseases common in population.
And also presence of common SNPs among the rare ones would have allowed in the recognition of rare snps also.
d. ) human population geneticists are interested in obtaining complete whole genome sequences to identify genes that must have recombined during meosis. Or to identify genes that must have mutated under some conditions. Or to identify mutations in genes that must have been seected over other. As these factors result in a different sequence and are also source of evolution..And also one of the reasons of why different human individuals have different appearances.
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