DNA, genes and the continuity of life
Describe the base pairing in DNA (write in complete detail/name)
Adenine pairs with thymine, and cytosine pairs with guanine
What is the result of meiosis?
Meiosis produces four haploid gametes, each genetically different
Which part of a nucleotide varies between adenine, thymine, cytosine and guanine?
The nitrogenous base is what differs between nucleotides
Evolution is best described as:
A. Change in an individual’s characteristics during its lifetime
B. Change in the genetic composition of a population over successive generations
C. Movement of organisms across geographic barriers
D. Increase in body size of animals over time
B — Evolution is change in the genetic composition of a population over successive generations.
Which of the following is not a mechanism of microevolution?
A. Gene flow
B. Genetic drift
C. Mutation
D. Photosynthesis
D — Photosynthesis is not a mechanism of allele-frequency change. The others are.
Which molecule carries the genetic code from DNA to the ribosome for protein synthesis?
mRNA carries the genetic code to the ribosome
Which type of mutation results from the failure of chromosomes to properly separate during cell division?
Nondisjunction is the failure of chromosomes to separate.
Which best explains why mitosis is important for multicellular organisms?
A. It produces gametes for reproduction.
B. It ensures growth, repair, and maintenance of tissues.
C. It introduces genetic variation into populations.
D. It increases the chromosome number in each cell.
B – Mitosis maintains growth, repair, and replacement of cells.
What is allopatric speciation?
Allopatric speciation occurs when populations are separated geographically
What kind of evidence might scientists use to infer the degree of evolutionary relatedness between two species?
DNA or protein sequence similarity is used to infer phylogenetic relationships.
Which process contributes to genetic variation by exchanging segments between homologous chromosomes during meiosis I?
Crossing over exchanges segments between homologous chromosomes
During DNA replication, which enzyme is responsible for unwinding the double helix?
Helicase unwinds the double helix
In transcription, the complementary RNA strand is produced from which DNA strand?
The template strand is used to build the complementary RNA sequence.
Which type of phenotypic selection favours intermediate phenotypes and tends to reduce variation in a population?
Stabilising selection favours the middle/average phenotypes and reduces extremes
Which pattern of diversification is described by species that are distantly related but evolve similar traits because they live in similar environments?
Convergent evolution: similar traits evolve in unrelated lineages because of similar selection pressures
Which of the following statements about non-coding DNA is FALSE?
A. Non-coding DNA includes introns within genes.
B. Non-coding DNA includes functional RNAs (like tRNA).
C. All non-coding DNA functions are fully understood.
D. Non-coding DNA includes telomeres and centromeres.
C – It is false that all non-coding DNA functions are fully understood.
In a monohybrid cross between two heterozygous individuals (Aa × Aa), what is the expected phenotypic ratio (dominant : recessive)?
The monohybrid cross produces a 3:1 phenotypic ratio.
Which sequence of steps correctly describes the process of creating recombinant DNA?
A. Insertion → cutting → amplification → joining
B. Cutting → insertion → joining → amplification
C. Amplification → cutting → insertion → joining
D. Joining → amplification → insertion → cutting
B – Cutting → insertion → joining → amplification is the correct sequence.
Genetic drift is more likely to have a strong effect on allele frequencies when:
A. The population size is large
B. Natural selection is very strong
C. The population size is small
D. Gene flow is high
C — Small populations are particularly susceptible to allele-frequency changes due to drift.
An evolutionary event in which a rapid increase in the number of species (after a mass extinction or when new habitats become available) is called...
Evolutionary radiation (often adaptive radiation) refers to rapid diversification of species from a common ancestor.
Which technique is used to amplify a specific segment of DNA to make many copies?
C – PCR (polymerase chain reaction) amplifies DNA segments.
A mutation changes a base in a codon from UCU (which codes for serine) to UCA (also serine). This is an example of:
A. Missense mutation
B. Nonsense mutation
C. Silent mutation
D. Frameshift mutation
C – A silent mutation changes a codon but not the amino acid.
Which pattern of inheritance is characterized by alleles that are located on the X chromosome and are expressed more often in males?
X-linked recessive traits are expressed more often in males.
Which of the following best describes a risk to species narrow genetic diversity under changing environmental conditions?
A. High gene flow will amplify rare beneficial alleles
B. Reduced genetic diversity can limit the ability to respond to new selective pressures, increasing extinction risk
C. Genetic drift in large populations leads to loss of alleles slower than in small populations
D. Speciation tends to occur faster in populations with low genetic variation
B — Reduced genetic diversity limits adaptive potential, so species are more vulnerable to environmental change and extinction
Which mode of speciation occurs when populations are in adjacent but non-overlapping habitats and there is some gene flow, yet selective pressures differ across the range?
Parapatric speciation is speciation with some, but reduced, gene flow due to differing environmental pressures across neighbouring habitats.