Quiz: Genetics

Explanation: The Hardy-Weinberg equation for heterozygote frequency is 2pq. With p = 0.6 and q = 0.4, the frequency is 2 * 0.6 * 0.4 = 0.48.

Explanation: Familial hypercholesterolaemia is most commonly caused by mutations in the LDLR gene, which encodes the low-density lipoprotein receptor.

Explanation: The 1:2:1 phenotypic ratio in the F2 generation, with an intermediate phenotype in the heterozygote, is characteristic of incomplete dominance.

Explanation: Huntington disease is a trinucleotide repeat disorder that exhibits anticipation, particularly when transmitted through the paternal line.

Explanation: Homeotic mutations cause one body part to develop in place of another, such as legs growing where antennae should be.

Explanation: Alpha-thalassaemia major can present with severe anaemia at birth due to the absence of alpha-globin chains.

Explanation: Tay-Sachs disease results from a deficiency of the enzyme hexosaminidase A, leading to the accumulation of GM2 ganglioside in neurons.

Explanation: A nonsense mutation changes a codon that specifies an amino acid into a stop codon, prematurely terminating translation.

Explanation: PCR uses short DNA primers and a thermostable DNA polymerase to replicate specific DNA sequences in vitro.

Explanation: Low maternal serum AFP is associated with Down syndrome (trisomy 21), whereas high levels are associated with neural tube defects.

Explanation: First cousins share, on average, 1/8 of their genes because they share one set of grandparents.

Explanation: RET is a proto-oncogene, while APC, NF1, and RB1 are tumor suppressor genes.

Explanation: In X-linked dominant inheritance, affected males transmit the trait to all their daughters but none of their sons.

Explanation: A 4-base recognition site occurs on average every 4^4 = 256 bp. For a 5,000 bp genome, the expected number of cuts is approximately 5,000 / 256 ≈ 20.

Explanation: Positional cloning is the process of mapping a gene to a chromosomal region and then identifying and cloning a genomic copy of the gene from that region.

Explanation: Exons are the coding sequences of a gene that are retained in the mature mRNA and translated into protein.

Explanation: The epigenetic inheritance system is often described as 'soft inheritance' because it involves changes in gene expression that are not due to changes in the DNA sequence.

Explanation: For an X-linked recessive trait, the frequency of affected males equals q (the allele frequency). If q = 1/100, then the frequency of affected homozygous females is q^2 = (1/100)^2 = 1 in 10,000.

Explanation: Waardenburg syndrome is a genetic condition characterized by hearing loss and changes in pigmentation, not a familial cancer syndrome.

Explanation: Arabidopsis is a small plant with a small genome size that can be raised inexpensively, making it an ideal model organism for plant genetics.

Explanation: Developmental plasticity is the ability of a single genotype to produce different phenotypes in response to environmental conditions during development.

Explanation: Cosmids and BACs (bacterial artificial chromosomes) can accommodate larger DNA inserts than standard phage vectors.

Explanation: Huntington disease is a classic example of an autosomal dominant disorder, as are Marfan syndrome and familial hypercholesterolaemia.

Explanation: A nucleotide consists of a phosphate group, a pentose sugar (ribose or deoxyribose), and a nitrogenous base.

Explanation: Amino acids are the building blocks of proteins, not DNA. DNA contains nucleotides with nitrogenous bases, phosphodiester bonds, and complementary base pairing.

Explanation: According to Chargaff's rules, adenine pairs with thymine. If adenine is 30%, thymine must also be 30%.

Explanation: Uracil is a pyrimidine base found in RNA but not in DNA. DNA contains thymine instead.

Explanation: Adenine and guanine are the purines, which have a double-ring structure. Cytosine, thymine, and uracil are pyrimidines.

Explanation: Transcription is the synthesis of RNA from a DNA template, catalyzed by RNA polymerase.

Explanation: In DNA gel electrophoresis, DNA fragments migrate toward the positive electrode (anode) because DNA is negatively charged due to its phosphate backbone.

Explanation: The Central Dogma states that genetic information flows from DNA to RNA (transcription) and then to protein (translation).

Explanation: Splicing is the process by which introns are removed from the primary RNA transcript and exons are joined together.

Explanation: The Meselson-Stahl experiment demonstrated that DNA replication is semi-conservative, where each new DNA molecule consists of one original and one newly synthesized strand.

Explanation: Long non-coding RNAs (lncRNAs) can act as molecular sponges for miRNAs, sequestering them and preventing them from regulating their target mRNAs.

Explanation: Z-DNA is favored by alternating purine-pyrimidine sequences, particularly those rich in guanine and cytosine, such as (GC)n repeats.

Explanation: Each PCR cycle doubles the number of DNA molecules. Starting from 1 copy, after n cycles, you have 2^n copies. To exceed 100, 2^7 = 128, so a minimum of 7 cycles is required.

Explanation: Pseudomonas aeruginosa is an obligate aerobe, meaning it requires oxygen to grow, which is relevant in the oxygen-rich environment of cystic fibrosis airways.

Explanation: Geobacillus stearothermophilus is a thermophilic, spore-forming bacterium that can survive commercial canning processes and cause spoilage, particularly in low-acid canned foods.

Explanation: Prions are the most resistant to sterilization, followed by bacterial spores, then enveloped viruses, and finally non-enveloped viruses.

Explanation: Plasmids are small, circular DNA molecules that are separate from the chromosomal DNA and are commonly found in bacteria.

Explanation: Innate immune responses include physical barriers, phagocytes, inflammation, and complement. Antibody production is a feature of adaptive immunity.