Genetics & Inheritance — Part 2: 34 MCQs with Explanations

Helicase breaks hydrogen bonds between base pairs, separating DNA strands to form replication fork.

Degeneracy means most amino acids are specified by more than one codon (e.g., leucine has 6 codons), providing mutation buffering.

In Mirabilis jalapa (four o'clock plant), red × white parents produce pink F1 flowers, showing intermediate phenotype.

Transformation involves uptake of 'naked' DNA fragments from surroundings (demonstrated by Griffith's experiment with Streptococcus).

Genetic drift causes random changes in allele frequencies, especially pronounced in small populations (founder effect, bottleneck effect).

X-linked recessive disorders (e.g., hemophilia, color blindness) affect males more frequently because they have only one X chromosome.

DNA polymerase III (prokaryotes) or δ/ε (eukaryotes) adds nucleotides to 3' end of growing strand during replication, proofreading for errors.

Helicase breaks hydrogen bonds between complementary base pairs, separating the two DNA strands to form the replication fork.

Hemophilia A (factor VIII deficiency) is X-linked recessive, predominantly affecting males who inherit the mutant allele from carrier mothers.

Degeneracy means most amino acids are encoded by more than one codon (e.g., leucine has 6 codons), providing protection against harmful effects of mutations.

Crossing over occurs during pachytene substage of prophase I, where non-sister chromatids exchange genetic material at chiasmata.

Incomplete dominance produces an intermediate phenotype (pink) in heterozygotes, distinct from either homozygous parent phenotype.

Transformation was demonstrated by Griffith (1928) using Streptococcus pneumoniae; Avery, MacLeod, and McCarty later identified DNA as the transforming principle.

Genetic drift includes founder effect (new population established by few individuals) and bottleneck effect (population size drastically reduced temporarily).

Males (XY) express X-linked recessive traits with a single mutant allele; females (XX) need two mutant alleles, making males affected more often.

DNA ligase catalyzes formation of phosphodiester bonds between adjacent Okazaki fragments after RNA primers are replaced with DNA.

HIV is a retrovirus with two identical single-stranded RNA molecules; reverse transcriptase converts RNA to DNA after infection.

DNA polymerase adds nucleotides to the 3' end of the growing strand in 5'→3' direction, using the template strand and requiring a primer.

Anaphase I: homologous chromosomes (each consisting of two sister chromatids) separate; sister chromatids remain attached at centromeres until anaphase II.

Gametes are haploid (n=23); fertilization restores diploid number (2n=46) in zygote.

Most bacteria have one circular chromosome in nucleoid; some also have smaller circular plasmids carrying accessory genes.

Central dogma: DNA → (transcription) → RNA → (translation) → protein. Transformation is bacterial uptake of foreign DNA, not part of information flow.

Cystic fibrosis results from homozygous recessive mutations in CFTR gene on chromosome 7, affecting chloride ion transport.

Gene is a segment of DNA that codes for a functional product (protein or RNA molecule) and is the basic unit of inheritance.

Klinefelter syndrome (47,XXY) affects males, causing tall stature, reduced facial/body hair, gynecomastia, and infertility.

Primase (a type of RNA polymerase) synthesizes short RNA primers (5-10 nucleotides) that provide 3'-OH group for DNA polymerase to begin synthesis.

Metaphase I: homologous pairs (bivalents) align randomly at metaphase plate; orientation of each pair is independent of others, generating genetic variation.

ABO system has three alleles (I^A, I^B, i); I^A and I^B are codominant (both expressed in AB blood type) and both dominant to recessive i allele.

Gene flow (migration) introduces new alleles or changes allele frequencies, reducing genetic differences between populations.

X-linked dominant: affected males (X^A Y) pass mutant allele to all daughters (X^A X) who are affected; sons receive Y chromosome and are unaffected.

DNA polymerase has 3'→5' exonuclease activity that removes incorrectly paired nucleotides during replication, maintaining fidelity.

Mutation creates new alleles; other mechanisms reshuffle existing alleles but do not create new genetic variation.

DNA serves as long-term genetic storage; RNA functions include information transfer (mRNA), amino acid delivery (tRNA), structural/catalytic roles (rRNA), and regulation.

DNA polymerase III (prokaryotes) or δ/ε (eukaryotes) adds nucleotides to 3' end of growing strand in 5'→3' direction using template strand.