SCSA Human Biology Science as a Human Endeavour

While mitochondrial DNA does code for enzymes involved in cellular respiration, this functional characteristic does not help scientists trace historical migration pathways.

Mitochondrial DNA is not identical within populations; in fact, the gradual accumulation of mutations over time creates distinct genetic markers (haplogroups) that scientists use to track migrations.

Mitochondrial DNA actually has a higher mutation rate than nuclear DNA due to its lack of protective histones and exposure to reactive oxygen species, so it is not more structurally stable.

While thalassemia affects haemoglobin, Tay-Sachs disease is caused by a mutation affecting the enzyme beta-hexosaminidase A, which is unrelated to haemoglobin.

Thalassemia is a genetic disorder affecting haemoglobin, but malaria is an infectious disease caused by a parasite, not a genetic mutation in the haemoglobin protein.

Sickle cell anaemia is caused by a mutation in haemoglobin, but malaria is a parasitic infection, not a genetic disorder found in the amino acid sequence of haemoglobin.

Cutting DNA at specific sites is the function of restriction enzymes (endonucleases), not PCR.

Determining the specific order of nucleotides is the goal of DNA sequencing, whereas PCR is used only for amplification.

Separating DNA fragments based on size is achieved through gel electrophoresis, not PCR.

This sequence differs from the human sequence at two positions (Lys instead of Ile, and Met instead of Glu), making it less similar than Option B.

This sequence differs from the human sequence at three positions (Asp, Leu, and Met), making it less similar than Option B.

This sequence differs from the human sequence at two positions (Val instead of Glu, and Asn instead of Ile), making it less similar than Option B.

This is incorrect because larger DNA fragments encounter more resistance from the gel matrix, causing them to migrate slower and travel a shorter distance than smaller fragments.

DNA is negatively charged due to its phosphate backbone, not positively charged, and therefore migrates toward the positive electrode (anode).

While DNA is negatively charged, the charge-to-mass ratio is constant for DNA fragments; therefore, separation is determined by the physical resistance (size) rather than differences in charge intensity.

Amino acid sequences accumulate mutations over time, making them highly useful for comparing genetic divergence and determining evolutionary relationships among different mammals.

Protein sequences provide valuable molecular data for constructing phylogenetic trees, as comparing their similarities and differences helps identify how closely related different species are.

Variations in bone structure (homologous structures) provide important morphological evidence that helps biologists distinguish and group different mammalian lineages.

Incorrect. While primers are required to start the process, the actual addition of new nucleotides to build the full DNA strand is not called priming.

Incorrect. Denaturation is the first step of PCR, where high heat is used to break hydrogen bonds and separate the double-stranded DNA into single strands.

Incorrect. Annealing is the second step of PCR, where the temperature is lowered to allow short DNA primers to bind to the single-stranded template before new nucleotides are added.

Species I and Species II differ by 2 amino acids. Since Species V has fewer differences, Species II is not the most closely related.

Species I and Species III differ by 5 amino acids. This high number of differences suggests they are more distantly related compared to the other options.

Species I and Species IV differ by 3 amino acids. Because there is another species with greater sequence similarity, this is not the correct answer.

While they share a recent common ancestor, identical protein sequences do not indicate that the two distinct species emerged at the exact same time.

Humans and chimpanzees having identical sequences means they are more closely related to each other than either is to Rhesus monkeys, contradicting the idea that they evolved from completely different primate lineages.

Evolution is a branching process, not a linear progression from one modern species to another. Humans, chimpanzees, and Rhesus monkeys all evolved from shared common ancestors at different points in time.

Primers bind to the template DNA via hydrogen bonding during the annealing phase, which does not require an enzyme. DNA polymerase instead catalyzes the addition of free nucleotides to the primer during the extension phase.

PCR utilizes a heat-stable DNA polymerase, such as Taq polymerase, to synthesize new DNA strands. RNA polymerase is used during transcription to synthesize RNA, not in PCR.

The amount of DNA doubles during each cycle of PCR, following exponential growth ($2^n$), rather than quadrupling.

Analyzing computerized genomic data of a single species describes bioinformatics or structural genomics, missing the essential comparison between different species.

Extracting chromosomes and mapping gene sequences refers to genome mapping, which does not inherently involve comparing genomes across different species.

Comparative genomics focuses exclusively on comparing genomes (DNA). Comparing proteins falls under proteomics, and comparing RNA falls under transcriptomics.

This option includes statement I, which is incorrect. DNA has a negatively charged phosphate backbone, so it moves from the negative electrode toward the positive electrode, not the other way around.

This option includes statement VII, which is incorrect. The gel matrix acts like a sieve, meaning larger pieces of DNA experience more resistance and move slower, not faster, than smaller pieces.

This option includes both statements I and VII, which are incorrect. DNA moves from the negative to the positive electrode due to its negative charge, and smaller pieces move faster through the gel than larger pieces.