# Biología Marina — Básico (A1/A2) 4: Genetics & DNA Replication > [Español] Biología Marina: Mendelian genetics, chromosome theory, DNA structure, replication mechanisms, and basic inheritance patterns - **Canonical URL:** https://flashcards.world/flashcards/sets/51a8f8d1-5c7d-4e2f-b207-eb5cfd033a6e/ - **Markdown URL:** https://flashcards.world/flashcards/sets/51a8f8d1-5c7d-4e2f-b207-eb5cfd033a6e.md - **Level:** basic - **Languages:** es → es - **Total Cards:** 32 ## Flashcards (32 Cards) | # | Front (Term / Prompt) | Back (Definition / Answer) | Example | Multiple-Choice Options | | :--- | :--- | :--- | :--- | :--- | | 1 | How 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. | | | | 2 | Which 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). | | | | 3 | During 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). | | | | 4 | What 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. | | | | 5 | What 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. | | | | 6 | What 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). | | | | 7 | What 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'. | | | | 8 | What enzyme catalyzes the formation of phosphodiester bonds to seal nicks between adjacent Okazaki fragments? | DNA ligase. | | | | 9 | What 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). | | | | 10 | What 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. | | | | 11 | What 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. | | | | 12 | What 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. | | | | 13 | What 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. | | | | 14 | What 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. | | | | 15 | What 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. | | | | 16 | What 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). | | | | 17 | How 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). | | | | 18 | What 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. | | | | 19 | What 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. | | | | 20 | Why 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. | | | | 21 | What causes Barr body formation in mammalian somatic cells? | Random epigenetic X-chromosome inactivation (lyonization) in females mediated by the non-coding RNA Xist. | | | | 22 | What enzyme relieves the torsional strain and positive supercoiling created ahead of the unwinding replication fork? | Topoisomerase (or DNA gyrase in prokaryotes). | | | | 23 | What 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. | | | | 24 | In 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. | | | | 25 | What 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). | | | | 26 | What enzyme unwinds the double helix at the replication fork by breaking hydrogen bonds between base pairs? | DNA helicase. | | | | 27 | According 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). | | | | 28 | What 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. | | | | 29 | How 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. | | | | 30 | Why 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. | | | | 31 | Which enzymatic activity allows replicative DNA polymerases to proofread and excise mispaired nucleotides immediately? | 3'-to-5' exonuclease activity. | | | | 32 | Why 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. | | | --- Study this deck interactively with FSRS-6 spaced repetition, audio review, and multiple-choice mode at [Flashcards World](https://flashcards.world/flashcards/sets/51a8f8d1-5c7d-4e2f-b207-eb5cfd033a6e/).