High School Biology : Genetics Principles

Study concepts, example questions & explanations for High School Biology

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Example Questions

Example Question #4 : Mutation

Which of the following is NOT a potential result from a point mutation that substitutes a single nucleotide in a gene?  

Possible Answers:

A codon that codes for a “stop” codon

A codon that codes for the same amino acid as the original sequence

A codon that cannot be transcribed into mRNA 

A codon that codes for a different amino acid

Correct answer:

A codon that cannot be transcribed into mRNA 

Explanation:

A point mutation that substitutes a single nucleotide within a gene alters the three nucleotides that make up an individual codon. There are four possible nucleotides and sixty-four possible codons, formed by 3-nucleotide sequences. Codons code for translation to one of the twenty amino acids. Changing a single nucleotide in the codon can have one of three effects.

First, it can result in a silent mutation. This is a result of the degeneracy of the genetic code, in which multiple codons can code for the same amino acid. Even though the sequence is different, the same amino acid is added. For example, if the sequence is initially CCT it will code for proline. If a mutation changes it to CCC it will still code for proline.

The second option is a missense mutation. In this case, the change in DNA sequence results in a codon for a different amino acid. For example, a mutation from TTT to TCT will change the amino acid from phenylalanine to serine.

Finally, the mutation could change a codon to a stop codon, causing early termination of translation. This is a nonsense mutation. For example, changing the TAT codon for tyrosine to TAA will result in an mRNA stop codon.

No matter how the point mutation affects the final protein product and codon sequence, it will still be transcribed into mRNA.

Example Question #61 : Genetics Principles

Which of the following types of mutation refers to the presence of a premature stop codon?

Possible Answers:

Radioactive mutation

Missense mutation

Frameshift mutation

Nonsense mutation

Silent mutation

Correct answer:

Nonsense mutation

Explanation:

A nonsense mutation results in a stop codon. This can be the result of an insertion or a deletion, causing a change in the DNA sequence from a normal amino acid codon to one of the three possible stop codon sequences.

A missense mutation changes the identity of a codon from one amino acid to another, resulting in a change to the protein primary structure. A silent mutation occurs when a mutation does not change the amino acid coded for by that codon. A frameshift mutation is an insertion or deletion that changes the reading frame of the entire protein and can have severe detrimental effects. A radioactive mutation is not a specific classification of mutations. 

Example Question #1 : Mutation

Scientists were examining the maize genome. They had two specimens: one control and one specimen that had undergone mutagenesis. They saw that the mutant specimen underwent a knockout caused by a nucleotide switch in the DNA. Is this a dominant or recessive mutation?

Possible Answers:

Recessive 

Dominant

Sex linked dominant

Cannot be determined 

Sex linked recessive 

Correct answer:

Dominant

Explanation:

This mutation is dominant because whatever mutation occurred at the genomic level was sufficient to cause an amino acid switch, i.e., it was expressed. If this were recessive, we would see that the nucleotide base change would not have yielded a knock out. Recall that only one copy of a "bad" gene is required for it to be expressed if it is a dominant mutation, whereas two copies of the "bad" gene are required for it to be expressed if it is a recessive mutation. No information is provided to consider sex linked traits.

Example Question #1 : Mutation

Scientists were examining the maize genome. They had two specimens: one control and one specimen that had undergone mutagenesis. They saw that the mutant specimen underwent a knockout caused by a nucleotide switch in the DNA.  However, when they compared gene sequences, they saw no change in size. Which type of mutation had most likely occurred?

Possible Answers:

Deletion 

Insertion

Substitution

Frameshift 

Nonsense mutation

Correct answer:

Substitution

Explanation:

The problem states that there was no change in gene size between the two specimens. That means that the mutant and the control still had the same number of nucleotide bases. Out of all options provided, substitution is the only possible type of mutation that fulfills the description. Deletion, insertion, nonsense and frameshift mutations would have all lead to a size discrepancy. 

Example Question #1 : Understanding Types Of Mutation

The starting sequence of a gene changed from AUGTTCGACGTG to AUGTTTCGACGTG. What type of mutation is this?

Possible Answers:

Translocation

Frameshift mutation

Missense mutation

Point mutation

Correct answer:

Frameshift mutation

Explanation:

The change introduces an extra "T' near the beginning of the sequence. This mutation will change the frame of the codons of the gene, and result in a frameshift mutation.

Example Question #66 : Genetics Principles

Scientists studying the genetics of a congenital disease analyzed the chromosomes of the patient and found a large portion of chromosome twenty-three in chromosome one, and a small part of chromosome one in chromosome twenty-three. What is this an example of?

Possible Answers:

Inversion

Deletion

Duplication

Translocation

Correct answer:

Translocation

Explanation:

Translocation is when two different chromosomes exchange large parts of the genetic sequence. 

Example Question #1 : Understanding Types Of Mutation

A single nucleotide polymorphism changes one nucleotide in a gene sequence. As a result, the gene gains a stop codon 500 base pairs to soon and the protein—when it is translated—is truncated or cut short. Which of the following types of mutations did the point mutation cause?

Possible Answers:

Frameshift mutation

None of these

Nonsense mutation

Missense mutation

Insertion

Correct answer:

Nonsense mutation

Explanation:

A nonsense mutation arises when a point mutation in DNA causes a mRNA strand to have a stop codon prematurely. It changes a base that would have led to an amino acid to a base that makes that triplet codon to a stop codon. This causes the ribosome to stop making the protein too soon and results in a shorter protein. The name arises from the drastic effect this has on the function of the protein. 

While biologically important, the other choices are incorrect. An insertion mutation changes the number of bases in that segment of DNA—extra is base added. On the other hand, a missense mutation switches one amino acid for another in that sequence. Last, a frameshift mutation changes the reading frame of three codons. So if a gene in DNA has the following sequence (keeping in mind that there are two strands not one):

ACTATTCCCGGATTC 

The resulting RNA sequence would be as follows:

UGAUAAGGGCCUAAG

A frameshift mutation would occur if a mutation caused thymine to be inserted into the first codon in the following DNA sequence:

ATCTATTCCCGGATTC

As a result, the resulting mRNA sequence would be the following:

UAGAUAAGGGCCUAAG

The entire reading frame has been changed. Because they have been moved over by one base all the triplet have been changed; therefore, each triplet is off by one base.

 

 

Example Question #61 : Genetics Principles

A transition is a mutation that includes a purine mutating to another purine or a pyrimidine mutating to another pyrimidine. 

Which option shows a transition mutation?

Possible Answers:

Thymine to guanine

Cytosine to thymine

Adenine to thymine

Guanine to cytosine

Adenine to guanine

Correct answer:

Adenine to guanine

Explanation:

Given the explanation provided, a transition is a mutation that mutates a purine to another purine, or a pyrimidine to another pyrimidine. The best way to solve is to assign the nucleotide as a purine or pyrimidine. To answer this, you must know that purines include adenine and guanine and pyrimidines include thymine, cytosine, and (in RNA) uracil. 

Example Question #1 : Understanding Mutation And Evolution

What distinguishes mutations from evolution?

Possible Answers:

Mutations happen to individuals while evolution happens to a species

Evolution affects organisms on a short term basis, while mutations are long term

Mutation and evolution are synonymous

Mutations do not get passed onto offspring, but evolution is inherited

Evolution happens to individuals while mutations happen to a species

Correct answer:

Mutations happen to individuals while evolution happens to a species

Explanation:

Mutations and evolution must be distinctly defined. Mutations happen to individuals. To acquire a mutation, a single event will cause the DNA of a single individual to become altered. If the result is a positive mutation, meaning the change helps increase the fitness of the individual (ability to reproduce), then it will get passed on to the next generation.

Evolution affects a population when mutations change the genetic variety of individuals. As a mutation spreads through the population by reproduction and inheritance it changes the genome of the species. As more and more mutations are acquired in the population, speciation can eventually occur.

Example Question #1 : Understanding Mutation And Evolution

Which of the following statements is incorrect?

Possible Answers:

Mutations are the source of new alleles

Radiation and chemical damage can cause mutations

Mutations create diversity among life-forms

Without mutations, there would be no evolution

Mutations happen when there is a need for a new trait in a population

Correct answer:

Mutations happen when there is a need for a new trait in a population

Explanation:

Mutations are not goal-directed. A mutation simply happens, and does not arise as a result of environmental necessities.

Alleles are different nucleotide sequences at a given gene's location. Different alleles generate different forms of the same protein product. Repair flaws caused by radiation and chemical damage change the nucleotide sequence, causing mutations. Mutations alter the gene pool, and are therefore the source of new alleles. These mutations are the foundation of evolutionary change and diversity among life-forms. 

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