微生物学 — 初級 (A1/A2) 4: Genetics & DNA Replication

[日本語] 微生物学: Mendelian genetics, chromosome theory, DNA structure, replication mechanisms, and basic inheritance patterns

Level
basic
Languages
ja → ja
Cards
32
Markdown
微生物学 — 初級 (A1/A2) 4: Genetics & DNA Replication (.md)

Flashcards (32)

#Front (Term / Question)Back (Definition / Answer)ExampleMultiple-Choice Options
1Why is the 'end-replication problem' unique to linear eukaryotic chromosomes rather than circular bacterial chromosomes?Removal of the terminal RNA primer on the lagging strand leaves a 5' gap that standard DNA polymerase cannot fill without an upstream 3'-OH.
2What is the function of single-stranded DNA-binding proteins (SSBs) at the replication fork?They bind to exposed single-stranded parental DNA to prevent premature re-annealing and degradation by nucleases.
3What is genetic linkage, and why does it violate Mendel's Law of Independent Assortment?Linkage occurs when genes located close together on the same chromosome tend to be inherited together unless separated by meiotic recombination.
4What is the lagging strand, and why is it synthesized discontinuously in Okazaki fragments?Because the lagging parental strand runs 5' to 3' toward the fork, synthesis must proceed away from the fork in short 5'-to-3' Okazaki fragments.
5What are the expected genotypic and phenotypic ratios in a monohybrid cross of two heterozygous individuals (Aa x Aa)?Genotypic ratio is 1 AA : 2 Aa : 1 aa; phenotypic ratio is 3 dominant : 1 recessive.
6How does incomplete dominance differ from codominance in heterozygous expression?In incomplete dominance, heterozygotes display an intermediate blended phenotype (e.g., red x white = pink); in codominance, both alleles are fully and simultaneously expressed (e.g., AB blood type).
7What enzyme relieves the torsional strain and positive supercoiling created ahead of the unwinding replication fork?Topoisomerase (or DNA gyrase in prokaryotes).
8What causes Barr body formation in mammalian somatic cells?Random epigenetic X-chromosome inactivation (lyonization) in females mediated by the non-coding RNA Xist.
9What does Mendel's Law of Segregation state regarding allele separation during gametogenesis?The two alleles for each gene segregate during meiosis so that each gamete carries only one allele for each gene.
10What enzyme resolves the end-replication problem in germ cells and stem cells, and what type of enzyme is it?Telomerase, a ribonucleoprotein reverse transcriptase (TERT) that carries its own internal RNA guide sequence.
11During which specific meiotic subphase does genetic crossing over (homologous recombination) occur?Prophase I of meiosis (specifically during the pachytene stage between non-sister chromatids of a homologous pair).
12What are telomeres, and what repetitive nucleotide sequence characterizes human telomeric ends?Repetitive non-coding heterochromatic caps at the ends of linear chromosomes with the conserved hexanucleotide repeat 5'-TTAGGG-3'.
13What does Mendel's Law of Independent Assortment state, and under what condition does it hold?Alleles of two or more different genes assort independently into gametes, provided the genes are on different chromosomes or far apart on the same chromosome.
14How do purines and pyrimidines differ in their chemical ring structures?Purines (adenine, guanine) have a two-ring bicyclic structure; pyrimidines (cytosine, thymine, uracil) have a single six-membered ring.
15According to Chargaff's rules, what are the quantitative base-pairing relationships in double-stranded DNA?The amount of adenine equals thymine (%A = %T) and guanine equals cytosine (%G = %C), meaning total purines (A+G) equal total pyrimidines (T+C).
16Which enzymatic activity allows replicative DNA polymerases to proofread and excise mispaired nucleotides immediately?3'-to-5' exonuclease activity.
17What is the definition of a recombinant frequency of 1% (or 1 map unit / centimorgan)?A 1% recombination frequency between two linked gene loci during meiotic crossing over.
18Which prokaryotic enzyme removes RNA primers and fills the resulting gaps with DNA nucleotides?DNA polymerase I (via its 5'-to-3' exonuclease and 5'-to-3' polymerase activities).
19What is a test cross in genetics, and how does it determine an individual's unknown genotype?Crossing an individual showing a dominant phenotype with a homozygous recessive individual; recessive offspring confirm heterozygosity.
20What is the distinction between an organism's genotype and its phenotype?Genotype is the specific genetic makeup and allelic combination; phenotype is the observable physical, physiological, or biochemical traits expressed.
21In what chemical direction does DNA polymerase synthesize a new daughter DNA strand?Exclusively in the 5'-to-3' direction, reading the parental strand in the 3'-to-5' direction.
22How many hydrogen bonds form between an A-T base pair versus a G-C base pair in double-stranded DNA?Adenine and thymine form 2 hydrogen bonds; guanine and cytosine form 3 hydrogen bonds.
23What enzyme unwinds the double helix at the replication fork by breaking hydrogen bonds between base pairs?DNA helicase.
24Why does DNA polymerase require an RNA primer synthesized by primase before initiating DNA synthesis?DNA polymerases cannot initiate nucleotide synthesis de novo; they require a free 3'-OH group to attach the incoming deoxynucleotide.
25What is the difference between pleiotropy and polygenic inheritance?Pleiotropy occurs when a single gene affects multiple distinct phenotypic traits; polygenic inheritance occurs when multiple independent genes influence a single continuous trait (e.g., human height).
26What is meant by the antiparallel orientation of double-stranded DNA?One strand runs in the 5'-to-3' direction (free 5' phosphate) while the complementary strand runs in the 3'-to-5' direction (free 3' hydroxyl).
27What is the leading strand during DNA replication, and how does its synthesis proceed relative to fork progression?The leading strand is synthesized continuously toward the replication fork in the same direction as fork movement.
28What enzyme catalyzes the formation of phosphodiester bonds to seal nicks between adjacent Okazaki fragments?DNA ligase.
29What is the genetic phenomenon where homologous chromosomes or sister chromatids fail to separate properly during meiosis?Nondisjunction, which leads to aneuploid gametes and conditions such as Trisomy 21 (Down syndrome).
30Why are X-linked recessive genetic disorders (e.g., hemophilia A, red-green colorblindness) more prevalent in biological males?Males are hemizygous (XY) and possess only one X chromosome; a single mutant allele on the X chromosome results in full disease expression.
31What did the classic Meselson-Stahl experiment demonstrate regarding the mechanism of DNA replication?DNA replicates via a semiconservative mechanism where each daughter duplex retains one parental strand and one newly synthesized strand.
32What is the classic phenotypic ratio expected from a dihybrid cross of two doubly heterozygous individuals (AaBb x AaBb)?9 dominant-dominant : 3 dominant-recessive : 3 recessive-dominant : 1 recessive-recessive (9:3:3:1).