SCSA Biology Heredity

Both spermatogenesis and oogenesis are forms of meiosis that result in the production of haploid gametes ($n$) from diploid germ cells ($2n$).

Spermatogenesis begins at puberty and continues throughout life, whereas oogenesis begins during fetal development, arrests, and resumes at puberty.

Both processes begin with diploid stem cells (spermatogonia and oogonia) that differentiate into diploid primary spermatocytes and oocytes before undergoing meiosis.

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.

This is incorrect because the sequence clearly contains nucleotides, meaning it must contain codons.

This is incorrect. Three is the number of nucleotides that make up a single codon, not the total number of codons in the given sequence.

This is incorrect. Twelve is the total number of individual nucleotides in the sequence, not the number of three-nucleotide codons.

An insertion would add a base to the sequence. The comparison shows that a nucleotide has been removed (deleted) rather than added, as the sequence has shifted to the left.

A substitution replaces one nucleotide with another without changing the length of the sequence. The observed change is a frameshift mutation caused by a deletion, which alters the reading frame of all subsequent codons.

This describes a substitution mutation. However, the sequences show that a base was removed entirely, causing the downstream sequence to shift, which characterizes a deletion mutation rather than a substitution.

Carbohydrates, such as glucose, are the substrates being broken down during metabolism, not the catalysts driving the reactions.

Nucleotides are the building blocks of DNA and RNA or act as energy carriers like ATP, rather than functioning as metabolic enzymes.

Lipids are primarily used for long-term energy storage and forming cell membranes, not for catalyzing biochemical reactions.

A polygenic trait is controlled by multiple genes, but the prompt specifies that this trait is determined by alleles of a single gene (the $C$ gene).

While the $c^h$ allele may be recessive to other alleles, the temperature-dependent change in fur color specifically demonstrates how the environment affects the expression of the trait, not its dominance or recessiveness.

The scenario describes the effect of temperature on a single gene's product, not an interaction between two different genes (epistasis).

Ionising radiation damages the DNA structure directly rather than targeting or inhibiting the enzymes involved in DNA replication, such as DNA polymerase.

While chemical mutagens or base analogs typically promote base mispairing, ionising radiation primarily causes severe structural damage to the DNA backbone.

Intercalating agents (like ethidium bromide), not ionising radiation, cause mutations by inserting themselves between DNA bases, which can lead to the insertion or deletion of nucleotides.

Incorrect. Fertilisation involves the random fusion of two haploid gametes to form a diploid zygote, rather than the random assortment of chromosomes during cell division.

Incorrect. Meiosis II involves the separation of sister chromatids, not the random assortment of homologous chromosome pairs, which already took place during meiosis I.

Incorrect. Mitosis produces genetically identical daughter cells and does not involve the pairing or random assortment of homologous chromosomes.

Codominance occurs when both alleles of a single gene are fully expressed in the heterozygote (e.g., AB blood type), resulting in discrete phenotypes rather than continuous variation.

Incomplete dominance describes a single-gene interaction where the heterozygote is intermediate between homozygotes, but it does not produce the broad continuous variation caused by multiple genes.

Multiple allele inheritance refers to the presence of more than two alleles for a single gene within a population (e.g., ABO blood groups), which typically results in distinct categories rather than continuous variation.

Incorrect. Measuring gene expression involves analyzing RNA levels using techniques like RT-qPCR or RNA sequencing, whereas DNA profiling looks at the DNA sequence itself.

Incorrect. While genetic markers can be used in population genetics, DNA profiling specifically focuses on identifying unique genetic patterns of individuals rather than tracking the movement of alleles between populations.

Incorrect. Creating transgenic organisms requires recombinant DNA technology and genetic engineering to insert foreign genes, which is entirely different from analyzing existing DNA profiles.

DNA ligase is essential for recombinant DNA technology as it acts as molecular glue to join the sugar-phosphate backbones of the DNA fragment and the vector.

Plasmid vectors are required to act as vehicles that carry the foreign DNA into a host cell for replication and maintenance.

Restriction enzymes are necessary to cut both the vector and the source DNA at specific sequences, creating compatible ends for insertion.

This describes the function of DNA helicase, which unwinds the double helix by breaking hydrogen bonds between base pairs.

This describes the function of DNA ligase, which joins DNA fragments (such as Okazaki fragments) together to form a continuous strand.

RNA primers are synthesized by the enzyme primase, not DNA polymerase, to initiate DNA synthesis.

This describes the function of DNA polymerase, the enzyme responsible for synthesizing new DNA strands, not histones.

Initiating replication involves specific initiator proteins and the origin recognition complex, whereas histones are primarily structural proteins involved in packaging.

Joining amino acids to form polypeptides is the function of ribosomes during translation, not histones.

Uracil is found in RNA, where it pairs with adenine. In DNA, thymine replaces uracil.

Guanine pairs with cytosine via three hydrogen bonds, not with adenine.

Cytosine pairs with guanine via three hydrogen bonds, not with adenine.