# Genetic Inheritance, Meiosis & DNA Replication > 32 genetics review cards on Mendelian and non-Mendelian inheritance, sex linkage and X-inactivation, meiotic recombination and aneuploidy, and DNA structure, semiconservative replication, repair, and telomeres. - **Canonical URL:** https://flashcards.world/flashcards/sets/817eb343-193e-4354-a0d1-0d89b14f7709/ - **Markdown URL:** https://flashcards.world/flashcards/sets/817eb343-193e-4354-a0d1-0d89b14f7709.md - **Level:** basic - **Languages:** en → en - **Total Cards:** 32 ## Flashcards (32 Cards) | # | Front (Term / Prompt) | Back (Definition / Answer) | Example | Multiple-Choice Options | | :--- | :--- | :--- | :--- | :--- | | 1 | Why does standard DNA replication need a primer before DNA polymerase extends a strand? | DNA polymerase adds nucleotides to an existing 3'-OH; it does not start a DNA chain from scratch. Primase supplies an RNA primer in the usual replication pathway. | | | | 2 | What ratios are expected from Aa × Aa with Mendelian segregation, equal viability and complete dominance? | Genotypes: 1 AA : 2 Aa : 1 aa. Phenotypes: 3 dominant : 1 recessive. These are expected probabilities, not guaranteed counts in a small family. | | | | 3 | How is a centimorgan related to recombination frequency for closely spaced loci? | For short intervals, 1 centimorgan (cM) corresponds approximately to 1% recombinant gametes. Multiple crossovers can make observed recombination underestimate the map distance across longer intervals. | | | | 4 | What does Mendel's law of segregation say about the two alleles at a diploid locus? | During gamete formation, the two alleles separate so that each gamete receives one. Under ordinary Mendelian segregation, either allele is equally likely to enter a gamete. | | | | 5 | Which enzyme separates DNA strands at a replication fork? | DNA helicase uses energy from ATP hydrolysis to unwind the duplex and separate the strands for copying. | | | | 6 | During which meiotic phase does crossing over occur, and between which chromatids? | During prophase I, between nonsister chromatids of paired homologous chromosomes. It exchanges corresponding DNA segments and can create new allele combinations. | | | | 7 | What is genetic linkage? | Nearby loci on the same chromosome tend to be inherited together more often than independent assortment predicts. Crossing over can separate their alleles; more distant loci can behave as though unlinked. | | | | 8 | How do incomplete dominance and codominance differ? | In incomplete dominance, the heterozygote phenotype is intermediate between the two homozygotes. In codominance, both allele-associated products or traits are detectable, as with A and B antigens in AB blood. The alleles remain distinct in both cases. | | | | 9 | Why are many X-linked recessive conditions more common in people with an XY chromosome complement? | They usually have only one copy of the relevant X-linked gene, so a pathogenic variant lacks a second X-linked copy that could mask its effect. Severity can vary, and people with two X chromosomes can also be affected. | | | | 10 | What base-amount relationships follow from canonical pairing in double-stranded DNA? | A = T and G = C; therefore, total purines (A + G) equal total pyrimidines (T + C). These relationships do not generally apply to a single DNA strand alone. | | | | 11 | How do purine and pyrimidine ring structures differ? | Purines such as adenine and guanine have fused six- and five-membered rings. Pyrimidines such as cytosine, thymine and uracil have one six-membered ring. | | | | 12 | What does antiparallel mean for the two strands of a DNA duplex? | Their sugar–phosphate backbones run in opposite directions: one 5' to 3', the other 3' to 5'. The labels describe backbone orientation, not a requirement for particular free groups at every DNA end. | | | | 13 | Why is the lagging strand synthesized as Okazaki fragments? | The templates are antiparallel, but DNA polymerase extends only 5' to 3'. The lagging strand is therefore made in short segments that grow away from the advancing fork and are later joined. | | | | 14 | What is meiotic nondisjunction? | Failure of homologous chromosomes or sister chromatids to separate properly. It can produce gametes with an extra or missing chromosome; after fertilization, this can cause aneuploidy such as trisomy 21. | | | | 15 | What is telomerase, and how does it extend telomeres? | It is a ribonucleoprotein enzyme. Its RNA component provides a template, and its TERT reverse-transcriptase subunit adds telomeric DNA repeats to a chromosome's 3' end. | | | | 16 | Which enzyme seals the remaining nicks between processed Okazaki fragments? | DNA ligase forms phosphodiester bonds between adjacent 3'-OH and 5'-phosphate ends after the gaps have been filled. | | | | 17 | What enzyme class relieves torsional strain ahead of a DNA replication fork? | Topoisomerases transiently break and rejoin DNA to change its topology. Bacterial DNA gyrase is one example that can remove positive supercoiling ahead of the fork. | | | | 18 | What do single-stranded DNA-binding proteins do at a replication fork? | They coat and stabilize exposed single-stranded DNA, helping prevent re-annealing and the formation of obstructive hairpin structures. | | | | 19 | What is a Barr body, and how is XIST involved? | A Barr body is a condensed, largely inactive X chromosome. XIST is a long noncoding RNA that coats the chromosome and helps establish silencing; some genes escape X inactivation. | | | | 20 | When does AaBb × AaBb give an expected 9:3:3:1 phenotypic ratio? | With Mendelian segregation, independent assortment, complete dominance at each locus, no epistasis and equal viability: 9 dominant at both loci, 3 dominant only at A, 3 dominant only at B, and 1 recessive at both. | | | | 21 | What activity removes a mispaired terminal nucleotide in proofreading DNA polymerases? | 3'-to-5' exonuclease activity removes the incorrect nucleotide from the growing strand's 3' end before synthesis continues. Not every DNA polymerase has this activity. | | | | 22 | When do two gene loci assort independently? | Loci on different chromosomes generally assort independently during normal meiosis. Far-apart loci on the same chromosome can have about 50% recombination and behave as though unlinked. | | | | 23 | How do genotype and phenotype differ? | Genotype is an organism's genetic makeup, including its alleles. Phenotype is its observable traits, which can reflect both genotype and environmental influences. | | | | 24 | How is the leading strand synthesized relative to replication-fork movement? | It is generally synthesized continuously in the 5'-to-3' direction, in the same overall direction as the advancing fork. | | | | 25 | How many hydrogen bonds occur in canonical Watson–Crick A–T and G–C base pairs? | A–T has 2 hydrogen bonds; G–C has 3. | | | | 26 | What are telomeres, and what repeat occurs in human telomeric DNA? | Telomeres are DNA–protein structures that protect the ends of linear chromosomes. The human G-rich telomeric strand typically contains tandem 5'-TTAGGG-3' repeats. | | | | 27 | In E. coli, which enzyme removes RNA primers and replaces them with DNA? | DNA polymerase I uses its 5'-to-3' exonuclease activity to remove primers and its polymerase activity to fill the resulting gaps with DNA. | | | | 28 | In what direction do replicative DNA polymerases extend a new DNA strand? | They synthesize 5' to 3', adding to the growing strand's 3' end while reading the template 3' to 5'. | | | | 29 | What replication model did the Meselson–Stahl experiment in E. coli support? | Semiconservative replication: each daughter DNA duplex contains one parental strand and one newly synthesized strand. | | | | 30 | How does a test cross help identify an unknown genotype? | Cross the dominant-phenotype individual with a homozygous recessive tester. Under simple Mendelian inheritance with complete dominance, recessive offspring show that the tested parent is heterozygous; no recessive offspring in a finite sample does not prove homozygosity. | | | | 31 | How do pleiotropy and polygenic inheritance differ? | Pleiotropy means one gene influences multiple traits. Polygenic inheritance means multiple genes contribute to one trait, such as height; the genes need not be independent, and the environment may also contribute. | | | | 32 | Why can removal of the final RNA primer leave a gap at a linear chromosome end? | In the usual lagging-strand model, removing the terminal primer leaves a 5'-end gap without an upstream 3'-OH from which DNA polymerase can extend. A circular chromosome has no equivalent free end. | | | --- Study this deck interactively with FSRS-6 spaced repetition, audio review, and multiple-choice mode at [Flashcards World](https://flashcards.world/flashcards/sets/817eb343-193e-4354-a0d1-0d89b14f7709/).