Problem 3 - Campbell Biology

Question

If the nucleotide variability of a locus equals \(0 \%,\) what is the gene variability and number of alleles at that locus? \begin{equation} \begin{array}{l}{\text { (A) gene variability }0 \%; \text { number of alleles }=0} \\ {\text { (B) gene variability }=0 \% \text { ; number of alleles }=1}\\\\{\text { (C) gene variability }=0 \% \text { ; number of alleles }=2} \\\ {\text { (D) gene variability }>0 \% \text { ; number of alleles }=2}\end{array}\end{equation}

Step-by-Step Solution

Answer

Option B: gene variability = 0%; number of alleles = 1.

Step 1: Understanding Nucleotide Variability

Nucleotide variability measures the genetic variation at the nucleotide level in a specific locus. If nucleotide variability is 0%, it means there is no variation in the nucleotide sequence at that locus.

Step 2: Analyzing Gene Variability

Gene variability refers to the variation in the genetic structure of a gene. If there is no variation at the nucleotide level (0% nucleotide variability), the gene variability will also be 0%, since no alternative forms (alleles) of the gene exist.

Step 3: Determining the Number of Alleles

With 0% nucleotide variability, the locus can only have one allele. This is because there are no variations in the nucleotide sequence to create different alleles.

Step 4: Conclusion

Given that both nucleotide variability and gene variability are 0%, and that there can only be one allele at the locus, the correct option is B: gene variability = 0%; number of alleles = 1.

Key Concepts

Nucleotide Variability

Nucleotide variability focuses on the genetic differences found at the smallest units of DNA, known as nucleotides. Imagine each nucleotide as a single letter in a very long book. When we measure nucleotide variability, we look at how often these 'letters' differ within the population at a particular spot in the book. If the nucleotide variability reads 0%, it means that this particular spot is identical across all individuals – no one has a different 'letter' there. This lack of difference signifies no genetic diversity at the nucleotide level for that locus.

Gene Variability

Gene variability refers to the diversity in the genetic structure of a particular gene. To understand this, let's consider a gene as a sentence made up of nucleotides (letters). If all the sentences are exactly the same, then there's no gene variability. Now, if the nucleotide variability at any locus is 0%, it means every individual has exactly the same letters in their genes at that point. Consequently, there will be no variation in the genetic structure (gene variability = 0%).
This is because there are no different versions (or alleles) of a gene when there's no nucleotide variation.

Number of Alleles

The number of alleles represents the different versions of a specific gene. Think of alleles as different metaphorical 'flavors' of a gene. If there's no nucleotide variation in the gene (0% nucleotide variability), then only one 'flavor' exists — implying there's just one allele at that locus. No genetic variation means there can't be multiple alleles because there's no variation at the DNA level to produce alternative gene versions.
In simpler terms, just as identical recipes produce identical cakes, identical nucleotide sequences produce identical alleles.Therefore, with 0% nucleotide variability, the number of alleles at that locus is one.