QCAA Biology Genetics and heredity

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.

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. This is half of the haploid number, but gametes contain the full haploid set of chromosomes, not half of it.

Incorrect. This is the diploid number ($2n=48$), which represents the chromosome count in somatic (body) cells, not reproductive sperm cells.

Incorrect. This is an arbitrary number that does not relate to the haploid ($n=24$) or diploid ($2n=48$) chromosome counts of an orangutan.

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.

A mutation occurring during meiosis in the dog would affect its gametes and potential offspring, not the dog's own body cells.

A mutation during mitosis in the dog would only affect the specific lineage of cells descended from that mutated cell, resulting in a mosaic rather than affecting all cells.

Mutations in a parent's somatic (body) cells are not passed down to their offspring; only mutations in germ cells are inherited.

Cri du chat syndrome is listed in the table as being caused by Monosomy 5, which involves chromosome 5 rather than the sex chromosomes.

Down syndrome is identified in the table as Trisomy 21, which involves an extra copy of chromosome 21, not the sex chromosomes.

Turner syndrome is listed as Monosomy 23, which implies a missing sex chromosome (genotype X0), whereas XXY indicates an extra chromosome.

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.

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).

BMP4 stands for Bone Morphogenetic Protein 4 and is involved in skeletal development, not the pigmentation or scale patterns of the fish.

Convergent evolution is a broad evolutionary pattern driven by similar environmental selective pressures, not a process directly controlled by a single gene like BMP4.

Sex determination in cichlids is controlled by a complex mix of other genetic and environmental factors, whereas BMP4 is specifically dedicated to bone and tissue development.

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.

This is incorrect because both Alpha and Beta Thalassemia are inherited as autosomal recessive conditions, not autosomal dominant.

This is incorrect because while Alpha Thalassemia involves four genes (two loci on chromosome 16), Beta Thalassemia involves only two genes (one locus on chromosome 11).

This is incorrect. Heterozygotes for Beta Thalassemia (Beta Thalassemia Minor) are typically asymptomatic or experience only mild anemia, making it non-fatal.

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.

While scientists use recombinant plasmids in biotechnology to produce human insulin, this is an artificial application. The natural function of CRISPR-Cas9 is immune defense, not acting as a plasmid.

A promoter is a DNA sequence where RNA polymerase binds to initiate transcription. CRISPR-Cas9 is an RNA-guided endonuclease complex that cuts DNA, not a transcriptional promoter.

Antibiotic resistance is typically conferred by specific genes that degrade or efflux antibiotics. CRISPR-Cas9 defends against foreign genetic material like viruses, not chemical antibiotics.