CHOOSE THE BEST ANSWER FOR EACH QUESTION

As humans spread around the world, they often adapted to local conditions, especially local diseases.

One example is the evolution of greater resistance to the pathogen that causes malaria. The evolution of greater resistance to malaria has been observed in human populations from three regions (South America, Western Africa, and Southeast Asia).

Recent genomic studies of these populations have identified several alleles related to malaria resistance that show evidence of positive selection based on SNP analysis. SNP is short for
[ Select ]
"selected-nucleotide process"
"single-nucleotide polymorphism"
"short-nucleotide pattern"
"sequenced-nucleotide partition"
.

What does it mean that these alleles show evidence of a "positive selection", from a genomic perspective?

[ Select ]
It is not possible to identify evidence of selection using SNPs.
These alleles will not have identifiable SNPs because they have not undergone genetic drift.
SNPs associated with these alleles will have a high frequency in these three regions relative to other regions.
NPs associated with these alleles will be rare in these three regions relative to other regions.

Question

CHOOSE THE BEST ANSWER FOR EACH QUESTION

As humans spread around the world, they often adapted to local conditions, especially local diseases.

One example is the evolution of greater resistance to the pathogen that causes malaria. The evolution of greater resistance to malaria has been observed in human populations from three regions (South America, Western Africa, and Southeast Asia).

Recent genomic studies of these populations have identified several alleles related to malaria resistance that show evidence of positive selection based on SNP analysis. SNP is short for 
[ Select ]
"selected-nucleotide process"
"single-nucleotide polymorphism"
"short-nucleotide pattern"
"sequenced-nucleotide partition"
 .

What does it mean that these alleles show evidence of a "positive selection", from a genomic perspective?

[ Select ]
It is not possible to identify evidence of selection using SNPs.
These alleles will not have identifiable SNPs because they have not undergone genetic drift.
SNPs associated with these alleles will have a high frequency in these three regions relative to other regions.
NPs associated with these alleles will be rare in these three regions relative to other regions.

BlackTom AI · Accepted Answer

Question restatement and option presentation:
- The prompt asks about two dropdown selections related to malaria resistance and SNPs. The first dropdown asks to identify what SNP stands for, and the second dropdown asks which statement describes what it means that these alleles show evidence of positive selection from a genomic perspective.

First dropdown options (for the meaning of SNP):
- selected-nucleotide process
- single-nucleotide polymorphism
- short-nucleotide pattern
- sequenced-nucleotide partition

Second dropdown options (for positive selection interpretation):
- It is not possible to identify evidence of selection using SNPs.
- These alleles will not have identifiable SNPs because they have not undergone genetic drift.
- SNPs associated with these alleles will have a high frequency in these three regions relative to other regions.
- NPs associated with these alleles will be rare in these three regions relative to other regions.

Option-by-option analysis:
- First dropdown option: 'selected-nucleotide process'
  This option is incorrect because the standard abbreviation SNP stands for single-nucleotide polymorphism. The phrase 'selected-nucleotide process' does not align with the widely used genetic terminology and would misrepresent what SNPs are. It misleadingly implies a process rather than a type of genetic variation.

- First dropdown option: 'short-nucleotide pattern'
  This choice is inaccurate since the established term is not about a pattern of nucleotides but about a specific kind of genetic variation at a single nucleotide position. It omits the concepts of variation (polymorphism) and the genetic context (nucleotide) that define SNPs.

- First dropdown option: 'sequenced-nucleotide partition'
  This is incorrect because it describes a technical procedure rather than the identity of the genetic marker. It confuses sequencing-related actions with the name of the variant type. SNP stands for something about nucleotide variation, not a partitioning or sequencing concept.

- First dropdown option: 'single-nucleotide polymorphism'
  This is the correct definition. 'Single' means one nucleotide position, 'nucleotide' indicates the DNA base, and 'polymorphism' denotes variation within a population. Together, they define a common type of genetic variation used in population genomics and selection studies.

- Second dropdown option: 'It is not possible to identify evidence of selection using SNPs.'
  This is incorrect because SNP data are routinely used to infer selection, including signals of positive selection, through patterns like allele frequency differences, extended haplotype structure, and fixation of beneficial variants. Hence, SNPs can provide evidence of selection.

- Second dropdown option: 'These alleles will not have identifiable SNPs because they have not undergone genetic drift.'
  This is incorrect in multiple ways. First, the presence or absence of SNPs is not determined by whether drift occurred for that particular allele; SNPs are simply single-base variations across individuals. Moreover, positive selection does not imply that drift did not occur. The claim also misstates the relationship between drift and detectable SNP signals.

- Second dropdown option: 'SNPs associated with these alleles will have a high frequency in these three regions relative to other regions.'
  This statement aligns with the concept of positive selection: alleles that confer an advantage (e.g., malaria resistance) often rise in frequency in populations under selective pressure. If malaria resistance alleles show evidence of positive selection in South America, Western Africa, and Southeast Asia, we expect their associated SNPs (or the haplotypes carrying them) to be more frequent in those regions than in regions without the selective pressure, reflecting selection rather than neutrality.

- Second dropdown option: 'NPs associated with these alleles will be rare in these three regions relative to other regions.'
  This option contains a couple of issues. It likely contains a typographical error ('NPs' instead of 'SNPs'), but more importantly, it contradicts the signature of positive selection in the stated regions. If alleles are under positive selection due to malaria resistance, their associated variants are typically not rare in the regions under selection; rather, they rise in frequency. Therefore this option is incorrect.

Why the two correct selections fit best together:
- The first correct choice clarifies what SNP stands for, establishing the proper genomic term to interpret the data.
- The second correct choice reflects a classic genomic interpretation of positive selection: alleles benefiting fitness in a particular environment (malaria-endemic regions) increase in frequency relative to other regions, making SNPs linked to those alleles more common in the selected populations. This is consistent with population genomics findings of elevated allele frequencies in the regions where malaria pressure is a driving factor.

In summary, the reasoning across options emphasizes: (a) correct terminology for SNPs, (b) correct interpretation of positive selection evidenced by elevated frequencies of associated SNPs in the populations under selection, and (c) identifying why the other distractors are inconsistent with standard population genetics concepts.

BIOL 1001 (001-013) Exam 3: Unit 3

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