Question

Among Betazoids in the world of Star Trek®, the ability to read minds is under the control of a gene called mindreader (abbre- viated \(m r\) ). Most Betazoids can read minds, but rare recessive mutations in the \(m r\) gene result in two alternative phenotypes: delayed-receivers and insensitives. Delayed-receivers have some mind-reading ability but perform the task much more slowly than normal Betazoids. Insensitives cannot read minds at all. Betazoid genes do not have introns, so the gene only contains coding DNA. It is 3332 nucleotides in length, and Betazoids use a four-letter genetic code. For each mutation, provide a plausible explanation for why it gives rise to its associated phenotype and not to the other phenotype. For example, hypothesize why the \(m r-1\) nonsense mutation in codon 829 gives rise to the milder delayed-receiver phenotype rather than the more severe insensitive phenotype. Then repeat this type of analysis for the other mutations. (More than one explanation is possible, so be creative within plausible bounds!)

Short answer

Answer: Different mutations in the mindreader gene can affect the protein's structure and function in various ways. For instance, the \(m r-2\) missense mutation might alter the active binding site, resulting in a reduced ability to receive signals, thus leading to the delayed-receiver phenotype. In contrast, the \(m r-3\) deletion mutation could cause a frameshift, disrupting the entire protein structure and rendering it nonfunctional, resulting in the insensitive phenotype.

Step-by-step solution

Understand the context

Before diving deeper into the problem, it is important to understand the context. Betazoids are a race from Star Trek® who are capable of reading minds, governed by a gene called mindreader (m r). Most Betazoids can read minds. However, recessive mutations in the m r gene can result in two alternative phenotypes: delayed-receivers, who read minds more slowly than usual, and insensitives, who cannot read minds at all.

Define the mutations

The exercise provides an example of the \(m r-1\) nonsense mutation in codon 829 giving rise to the milder delayed-receiver phenotype rather than the more severe insensitive phenotype. We are tasked to repeat this type of analysis for the other mutations. Since the exercise does not explicitly provide details about these other mutations, we will make up two plausible mutations: 1. \(m r-2\): A missense mutation in codon 1230. 2. \(m r-3\): A deletion mutation removing three consecutive nucleotides in codon 2030.

Create explanations for each mutation

1. \(m r-2\) mutation: Possible explanation: The \(m r-2\) missense mutation occurs in codon 1230, which might be involved in forming the active binding site for the m r protein. The mutation could lead to a change in the amino acid sequence, resulting in a less-efficient binding process and reduced ability to receive signals from other minds. Hence, the mutation exhibits the delayed-receiver phenotype. 2. \(m r-3\) mutation: Possible explanation: The deletion mutation \(m r-3\) occurs in codon 2030 and causes a frameshift in the genetic code, potentially leading to the subsequent downstream region being translated into a completely different amino acid sequence. This could disrupt the overall structure and functionality of the m r protein to the point that it no longer functions. Consequently, individuals with this mutation would be insensitive towards reading minds.

Evaluate the explanations

Finally, we must evaluate our created explanations to ensure they are within plausible bounds for the mindreader gene in the context of Betazoids. As long as we remain within the scope of the given information about the gene, its characteristics, and the phenotypes associated with mutations, the explanations provided for \(m r-2\) and \(m r-3\) are feasible.

Key concepts

Nonsense Mutation

In genetics, a nonsense mutation is a specific type of mutation wherein the genetic code is altered in a way that leads to the premature termination of protein synthesis. This is due to the introduction of a stop codon in place of a codon that would normally specify an amino acid. As a result, the synthesis of the polypeptide is halted too soon, typically resulting in a truncated and often nonfunctional protein.

For example, in the context of the Betazoid population from Star Trek®, the nonsense mutation denoted as 'm r-1' in codon 829 changes a normal codon into a stop codon. This causes the translation process to stop prematurely, yielding a shorter-than-normal protein that might retain some functionality but at a reduced efficiency. This could plausibly explain the milder delayed-receiver phenotype as opposed to the more severe insensitive phenotype, since some residual protein activity might still allow for slow mind-reading capabilities.

Frameshift Mutation

Frameshift mutations are a type of genetic mutations that involve an insertion or deletion of nucleotides in the DNA sequence, which alters the reading frame of the genetic code. Since the genetic code is read in groups of three nucleotides, or codons, the addition or loss of nucleotides can shift the frame and change every codon after the mutation.

This alteration can lead to the production of utterly different proteins, with different amino acids or even a premature stop codon if a frameshift occurs. For instance, the hypothetical 'm r-3' mutation in our Betazoid gene scenario, where three consecutive nucleotides are deleted, would likely shift the reading frame causing a completely different and possibly nonfunctional protein to be produced. This dramatic alteration in the genetic code could explain why individuals with this mutation exhibit the insensitive phenotype, completely lacking the ability to read minds.

Genetic Code

The genetic code is the set of rules by which information encoded within genetic material (DNA or RNA sequences) is translated into proteins by living cells. It is essentially the language that tells the cell's machinery which amino acids to add next during protein synthesis, based on sequences of three nucleotides called codons. There are 64 possible codons, coding for 20 amino acids plus the stop signals that mark the end of a protein-building sequence.

In the case of Betazoids, it's mentioned that they use a four-letter genetic code, referring to the four nucleotides that make up DNA: adenine (A), cytosine (C), guanine (G), and thymine (T). Their ability to read minds is encoded within a 3332-nucleotide gene, which is read and interpreted using this genetic code to produce a specific protein that facilitates their telepathic ability. The genetic code is universal among most organisms, but even a single change within it can greatly affect the phenotypic expression of a trait, as seen with the mindreader gene.

Phenotypic Expression

Phenotypic expression refers to the observable traits or characteristics of an organism, which result from the interactions between its genetic makeup (genotype) and the environment. This expression encompasses everything from physical appearance to behavioral traits and physiological functions. In genetics, mutations can influence phenotypic expression by altering the type, function, and efficiency of the proteins produced.

Within the context of the textbook example, the Betazoid race expresses two distinct phenotypes concerning mind-reading abilities due to mutations in the 'mindreader' gene. Those with 'delayed-receiver' phenotype have slower mind-reading capabilities likely due to partial functionality of the m r protein, while 'insensitives' completely lack this ability, possibly because of a full loss of function in the protein resulting from a more severe mutation such as a frameshift. Understanding how genetic changes affect phenotypic expression can provide insights into the mechanisms of inheritance and evolution.