Keystone Biology: Genetics and Evolution Questions and Answers 1 — Questions and Answers
Question 1: A population of insects is sprayed with a new insecticide. Most of the insects are killed, but a few individuals survive. These survivors reproduce, and in the next generation, a significantly higher percentage of the population is resistant to the insecticide. Which principle of evolution does this scenario best illustrate?
- Gene flow
- Natural selection (Correct answer)
- Genetic drift
- Artificial selection
Correct answer: Natural selection
This is an example of natural selection. The insecticide acts as an environmental pressure, 'selecting' for individuals with a pre-existing trait for resistance. These resistant individuals are more likely to survive and reproduce, passing the resistance trait to their offspring, which leads to an increase in the frequency of this trait in the population over time.
Question 2: Which of the following correctly describes the central dogma of molecular biology, representing the flow of genetic information to synthesize a protein?
- Protein → RNA → DNA
- RNA → DNA → Protein
- DNA → RNA → Protein (Correct answer)
- DNA → Protein → RNA
Correct answer: DNA → RNA → Protein
The central dogma of molecular biology states that the flow of genetic information is from DNA to RNA to protein. First, the DNA sequence of a gene is copied into messenger RNA (mRNA) through a process called transcription. Then, the mRNA sequence is used as a template to build a protein through a process called translation.
Question 3: The wing of a bat, the flipper of a whale, and the arm of a human all share a similar underlying bone structure, despite being used for different functions (flying, swimming, and grasping). What term best describes these structures?
- Vestigial structures
- Analogous structures
- Homologous structures (Correct answer)
- Convergent structures
Correct answer: Homologous structures
These are homologous structures. Homologous structures are features shared by related species because they have been inherited from a common ancestor. Even though they have been adapted for different functions in different species, their similar underlying anatomy points to a shared evolutionary origin.
Question 4: During the process of meiosis, homologous chromosomes can exchange segments of DNA. This process is known as crossing over. What is the most significant outcome of this event?
- It ensures the daughter cells are identical to the parent cell.
- It increases genetic variation in the resulting gametes. (Correct answer)
- It doubles the chromosome number for the new organism.
- It repairs any DNA damage that occurred during replication.
Correct answer: It increases genetic variation in the resulting gametes.
The primary significance of crossing over is the creation of new combinations of alleles on the chromosomes. This recombination of genetic material results in gametes (sperm and egg cells) that are genetically different from each other and from the parent cell, thereby increasing the genetic variation within a population.
Question 5: A frameshift mutation, caused by the insertion or deletion of a nucleotide, is often more damaging to the resulting protein than a point mutation (substitution). Which of the following best explains why?
- It causes the DNA to become unstable and break apart.
- It alters the reading frame of the genetic code, changing all codons downstream from the mutation. (Correct answer)
- It only affects the very last amino acid in the protein chain.
- It is always corrected by repair enzymes before translation occurs.
Correct answer: It alters the reading frame of the genetic code, changing all codons downstream from the mutation.
A frameshift mutation shifts how the sequence of nucleotide bases is read in three-letter codons. This change in the 'reading frame' alters every amino acid that is coded for after the point of the mutation, which typically results in a completely different and nonfunctional protein. A point mutation, in contrast, usually only affects a single amino acid.
Question 6: In pea plants, the allele for tall stems (T) is dominant to the allele for short stems (t). If a heterozygous tall plant (Tt) is crossed with a short plant (tt), what percentage of the offspring is expected to have a heterozygous genotype?
- 0%
- 25%
- 75%
- 50% (Correct answer)
Correct answer: 50%
Using a Punnett square for the cross (Tt x tt), the possible genotypes for the offspring are Tt and tt. The Tt parent can contribute a T or a t allele, while the tt parent can only contribute a t allele. The results show that two of the four squares (or 50%) will have the heterozygous genotype (Tt) and two of the four squares (50%) will have the homozygous recessive genotype (tt).
Keystone Biology: Genetics and Evolution Questions and Answers 1
A population of insects is sprayed with a new insecticide.
Most of the insects are killed, but a few individuals survive.
These survivors reproduce, and in the next generation, a significantly higher percentage of the population is resistant to the insecticide.
Which principle of evolution does this scenario best illustrate?