Essentials of Genetics, 10th Edition - 2025/2026 Study Guide

Essentials of Genetics, 10th Edition - 2025/2026 Study Guide Chapter 1: Introduction to Genetics 1. What is the primary molecule of genetic information in living organisms? ANSWER Deoxyribonucleic Acid (DNA). 2. What are the three major subdisciplines of genetics? ANSWER Transmission genetics, molecular genetics, and population genetics. 3. What is the central dogma of molecular biology? ANSWER It describes the flow of genetic information: DNA is transcribed into RNA, which is then translated into a protein. 4. How did Gregor Mendel contribute to the field of genetics? ANSWER He established the fundamental principles of inheritance through his experiments with pea plants, forming the basis of transmission genetics. Chapter 2: Mitosis and Meiosis 5. What is the primary purpose of mitosis? ANSWER To produce two genetically identical daughter cells for growth, repair, and asexual reproduction. 6. What is the primary purpose of meiosis? ANSWER To produce four genetically non-identical haploid gametes (sperm and egg cells) for sexual reproduction. 7. What is the significance of synapsis and crossing over in meiosis? ANSWER Synapsis brings homologous chromosomes together, and crossing over (in Prophase I) exchanges genetic material between them, increasing genetic diversity in offspring. 8. Describe the key difference in the outcome of mitosis versus meiosis. ANSWER Mitosis results in two diploid, identical cells. Meiosis results in four haploid, genetically diverse cells. 9. At what stage of meiosis do homologous chromosomes separate? ANSWER Anaphase I. 10. At what stage of meiosis do sister chromatids separate? ANSWER Anaphase II. Chapter 3: Mendelian Genetics 11. What is the difference between an organism's genotype and its phenotype? ANSWER Genotype is the genetic makeup (e.g., Bb). Phenotype is the observable physical or biochemical characteristic (e.g., brown eyes). 12. According to Mendel's Law of Segregation, what happens to alleles during gamete formation? ANSWER The two alleles for a heritable character segregate (separate) during gamete formation so that each gamete carries only one allele for each gene. 13. What is the expected phenotypic ratio from a dihybrid cross between two heterozygotes? ANSWER 9:3:3:1. 14. How can a testcross be used to determine the genotype of an individual with a dominant phenotype? ANSWER The individual is crossed with a homozygous recessive individual. If any offspring show the recessive trait, the unknown genotype must be heterozygous. 15. What does Mendel's Law of Independent Assortment state? ANSWER Alleles of different genes assort independently of one another during gamete formation, provided the genes are on different chromosomes or far apart on the same chromosome. Chapter 4: Extensions of Mendelian Genetics 16. What is incomplete dominance? Provide an example. ANSWER The heterozygous phenotype is intermediate between the two homozygous phenotypes. Example: A cross between a red and a white snapdragon produces pink offspring. 17. What is codominance? Provide an example. ANSWER Both alleles in a heterozygote are fully expressed. Example: The ABO blood group system, where the I^A and I^B alleles are both expressed in the AB blood type. 18. What are multiple alleles? ANSWER When a gene has more than two possible allelic forms in a population. Example: The ABO blood group has three alleles: I^A, I^B, and i. 19. How can a single gene affect multiple, seemingly unrelated phenotypes? ANSWER This is called pleiotropy. Example: The allele for sickle cell anemia affects red blood cell shape, but also causes anemia, organ damage, and increased resistance to malaria. 20. What is epistasis? ANSWER The phenomenon where the expression of one gene masks or modifies the effect of a second gene. Chapter 5: Chromosome Mapping in Eukaryotes 21. What is genetic linkage? ANSWER The tendency for genes located close together on the same chromosome to be inherited together. 22. How does crossing over during meiosis affect linked genes? ANSWER It separates linked alleles, producing recombinant gametes and recombinant offspring. 23. What is a genetic map unit (centimorgan, cM)? ANSWER A unit of distance on a genetic map that corresponds to a 1% recombination frequency. 24. Why is the observed frequency of recombinant offspring never more than 50%? ANSWER Because when genes are on different chromosomes (or very far apart on the same one), they assort independently, producing 50% recombinant and 50% parental types, which is the maximum. Chapter 6: Genetic Analysis and Mapping in Bacteria and Bacteriophages 25. What is the difference between transformation, conjugation, and transduction in bacteria? ANSWER Transformation is the uptake of free DNA from the environment. Conjugation is the direct transfer of DNA via a pilus. Transduction is the transfer of DNA from one bacterium to another by a virus (bacteriophage). 26. What is an Hfr (High-frequency recombination) strain? ANSWER A bacterial strain with the F plasmid integrated into its chromosome. During conjugation, it can transfer chromosomal genes at a high frequency. 27. How are bacteriophages used to map bacterial genes? ANSWER Through transduction mapping, where the co-transduction of two genes indicates they are close together on the bacterial chromosome. Chapter 7: Sex Determination and Sex Chromosomes 28. What is the typical sex chromosome constitution for a human male and a human female? ANSWER Male: XY. Female: XX. 29. What is meant by "X-inactivation" in female mammals? ANSWER The process where one of the two X chromosomes in each female somatic cell is randomly inactivated and condensed into a Barr body, ensuring dosage compensation. 30. What is a sex-linked gene? ANSWER A gene located on a sex chromosome (usually the X chromosome). 31. Why are X-linked recessive disorders more common in males? ANSWER Because males have only one X chromosome. If they inherit a recessive allele on their X, they will express the disorder, as they have no second allele to mask it. Chapter 8: Chromosome Mutations: Variation in Number and Arrangement 32. What is nondisjunction? ANSWER The failure of chromosomes to separate properly during meiosis I or meiosis II. 33. What is the genetic cause of Down syndrome? ANSWER Trisomy 21, the presence of three copies of chromosome 21. 34. What is a polyploid organism? ANSWER An organism that has more than two complete sets of chromosomes (e.g., 3n, 4n). 35. What is the difference between a deletion and a duplication chromosome mutation? ANSWER A deletion is the loss of a chromosomal segment. A duplication is the repetition of a chromosomal segment. 36. What is a pericentric inversion? ANSWER An inversion that includes the centromere. Chapter 9: DNA Structure and Analysis 37. What are the three components of a DNA nucleotide? ANSWER A deoxyribose sugar, a phosphate group, and a nitrogenous base (A, T, G, or C). 38. How did the Hershey-Chase experiment conclude that DNA is the genetic material? ANSWER They used bacteriophages to show that only the DNA, not the protein coat, enters the bacterial cell to produce new phage particles. 39. What is Chargaff's rule? ANSWER In DNA, the amount of Adenine equals Thymine (A=T), and the amount of Guanine equals Cytosine (G=C). 40. Describe the double-helix structure of DNA as proposed by Watson and Crick. ANSWER Two antiparallel polynucleotide chains twisted around a central axis. The sugar-phosphate backbones form the outside, and the nitrogenous bases pair specifically (A-T, G-C) on the inside, held by hydrogen bonds. Chapter 10: DNA Replication and Recombination 41. What is meant by DNA replication being "semiconservative"? ANSWER Each newly synthesized DNA molecule consists of one old (parental) strand and one new (daughter) strand. 42. What is the function of DNA polymerase III in E. coli? ANSWER It is the primary enzyme responsible for synthesizing new DNA strands by adding nucleotides to the 3' end of a growing chain. 43. Why is an RNA primer required for DNA replication? ANSWER DNA polymerase cannot initiate synthesis on a bare template strand; it can only add nucleotides to an existing 3'-OH group. The RNA primer provides this starting point. 44. What is the key difference between the leading and lagging strands? ANSWER The leading strand is synthesized continuously in the 5' to 3' direction toward the replication fork. The lagging strand is synthesized discontinuously away from the fork in short fragments called Okazaki fragments. 45. What enzyme joins the Okazaki fragments on the lagging strand? ANSWER DNA ligase. Chapter 11: Chromosome Structure and DNA Sequence Organization 46. What are nucleosomes? ANSWER The fundamental repeating units of chromatin, consisting of DNA wrapped around a core of eight histone proteins. 47. What is the difference between euchromatin and heterochromatin? ANSWER Euchromatin is less condensed, genetically active, and rich in genes. Heterochromatin is highly condensed, genetically inactive, and often rich in repetitive sequences. 48. What are telomeres and what is their function? ANSWER The protective, repetitive DNA sequences at the ends of linear chromosomes. They prevent the loss of genetic information during replication and protect chromosome ends from degradation. Chapter 12: The Genetic Code and Transcription 49. What is a codon? ANSWER A three-nucleotide sequence in mRNA that specifies a particular amino acid or a stop signal. 50. What are the key characteristics of the genetic code? ANSWER It is triplet, unambiguous, degenerate/redundant, commaless, and nearly universal. 51. What is the role of RNA polymerase in transcription? ANSWER It catalyzes the synthesis of an RNA strand complementary to a DNA template strand. 52. What are the three main stages of transcription? ANSWER Initiation, elongation, and termination. 53. What modifications are made to a eukaryotic pre-mRNA before it exits the nucleus? ANSWER A 5' cap is added, a 3' poly-A tail is added, and introns are removed by RNA splicing. Chapter 13: Translation and Protein Synthesis 54. What is the function of transfer RNA (tRNA)? ANSWER tRNA molecules carry specific amino acids to the ribosome and have an anticodon that base-pairs with the complementary mRNA codon. 55. What is the role of the ribosome in translation? ANSWER The ribosome is the molecular machine that facilitates the coupling of tRNA anticodons with mRNA codons and catalyzes the formation of peptide bonds between amino acids. 56. What are the A, P, and E sites of a ribosome? ANSWER A site: binds the incoming aminoacyl-tRNA. P site: holds the tRNA carrying the growing polypeptide chain. E site: the exit site for deacylated tRNA. 57. What is a missense mutation? ANSWER A point mutation that changes a single amino acid in the protein. 58. What is a nonsense mutation? ANSWER A point mutation that changes a sense codon into a stop codon, leading to a truncated protein. 59. What is a frameshift mutation? ANSWER An insertion or deletion of nucleotides that is not a multiple of three, which alters the reading frame and drastically changes the resulting protein. Chapter 14: Gene Mutation, DNA Repair, and Transposition 60. What is a spontaneous mutation? ANSWER A mutation that arises from natural biological or chemical processes in the cell, without a known causative agent. 61. What is the primary function of the proofreading activity of DNA polymerase? ANSWER To recognize and remove incorrectly incorporated nucleotides during DNA replication, improving fidelity. 62. Describe the process of nucleotide excision repair. ANSWER A system that removes and replaces a segment of a DNA strand containing a bulky lesion (like a thymine dimer). Enzymes cut the strand on either side of the damage, the segment is removed, and DNA polymerase fills in the gap. 63. What is a transposable element (transposon)? ANSWER A DNA sequence that can move ("jump") from one location in the genome to another. Chapter 15: Regulation of Gene Expression in Bacteria 64. What is an operon? ANSWER A cluster of prokaryotic genes under the control of a single promoter and regulatory region, transcribed together into a single mRNA molecule. 65. Describe how the lac operon is inducible. ANSWER In the absence of lactose, a repressor protein binds to the operator and prevents transcription. When lactose is present, it acts as an inducer, binding to the repressor and inactivating it, allowing transcription to occur. 66. What is the role of cAMP and CAP in the lac operon? ANSWER They function in positive regulation. When glucose is low, cAMP levels are high. cAMP binds to CAP, and the cAMP-CAP complex binds to the promoter, enhancing RNA polymerase binding and increasing transcription of the lac operon. Chapter 16: Regulation of Gene Expression in Eukaryotes 67. What are transcription factors? ANSWER Proteins that bind to regulatory sequences (like enhancers and promoters) and influence the recruitment of RNA polymerase to initiate transcription. 68. How does DNA methylation typically affect gene expression? ANSWER It usually represses transcription by making the DNA less accessible to transcription machinery. 69. How does histone acetylation affect gene expression? ANSWER It usually promotes transcription by loosening the association between DNA and histones, making the DNA more accessible. 70. What are non-coding RNAs, and how can they regulate gene expression? ANSWER RNAs that are not translated into protein. Example: microRNAs (miRNAs) can bind to complementary mRNA sequences, leading to the blocking of translation or degradation of the mRNA. Chapter 17: Recombinant DNA Technology 71. What are restriction enzymes? ANSWER Bacterial enzymes that cut DNA at specific recognition sequences, producing "sticky ends" or "blunt ends." 72. What is a plasmid vector? ANSWER A small, circular DNA molecule, often derived from bacteria, that is used to carry foreign DNA into a host cell for cloning. 73. What is the purpose of the polymerase chain reaction (PCR)? ANSWER To amplify a specific target DNA sequence in vitro, producing millions of copies in a few hours. 74. What are the key steps in a single PCR cycle? ANSWER Denaturation (separating DNA strands), Annealing (primers bind to target sequences), and Extension (DNA polymerase synthesizes new strands). 75. What is DNA sequencing used for? ANSWER To determine the precise nucleotide order of a DNA fragment. Chapter 18: Genomics, Bioinformatics, and Proteomics 76. What is structural genomics? ANSWER The branch of genomics that focuses on determining the three-dimensional structure of every protein encoded by a genome. 77. What is a SNP (Single Nucleotide Polymorphism)? ANSWER A variation in a single DNA nucleotide at a specific position in the genome among individuals. 78. What is the goal of proteomics? ANSWER To identify and characterize the entire set of proteins (the proteome) expressed by a cell, tissue, or organism at a given time. Chapter 19: Applications of Genetic Engineering and Biotechnology 79. How is CRISPR-Cas9 technology used in genetics? ANSWER It is a powerful gene-editing tool that uses a guide RNA and the Cas9 enzyme to make precise double-strand breaks in DNA at specific locations, allowing for gene knockout, correction, or insertion. 80. What is the purpose of creating a transgenic organism? ANSWER To introduce a gene from one species into the genome of another to study gene function or to confer a desirable trait (e.g., pest resistance in plants). 81. What is gene therapy? ANSWER An experimental technique that uses genes to treat or prevent disease by introducing, removing, or altering genetic material within a patient's cells. Chapter 20: Developmental Genetics 82. What are homeotic (Hox) genes? ANSWER A group of genes that control the body plan of an embryo along the head-tail axis, determining the identity of body segments. 83. How does apoptosis contribute to normal development? ANSWER It is programmed cell death that sculpts structures by removing unnecessary cells, such as the webbing between human fingers and toes during embryonic development. Chapter 21: Cancer Genetics 84. What is the difference between a proto-oncogene and an oncogene? ANSWER A proto-oncogene is a normal gene that promotes cell growth and division. An oncogene is a mutated version of a proto-oncogene that promotes uncontrolled cell division (it is a "gain-of-function" mutation). 85. How do tumor suppressor genes normally function, and what happens when they are mutated? ANSWER They encode proteins that slow or stop cell division, repair DNA mistakes, or trigger apoptosis. When both copies are inactivated ("loss-of-function" mutations), cell division can proceed uncontrollably. 86. What is the "two-hit hypothesis" for tumor suppressor genes? ANSWER It proposes that both alleles of a tumor suppressor gene must be mutated or inactivated for cancer to develop. Chapter 22: Quantitative Genetics and Multifactorial Traits 87. What is a quantitative (polygenic) trait? ANSWER A trait influenced by multiple genes and often the environment, showing continuous variation in a population (e.g., human height, skin color). 88. What is heritability in the broad sense (H²)? ANSWER The proportion of total phenotypic variance in a population that is due to genetic variance. Chapter 23: Population Genetics 89. What is the Hardy-Weinberg equilibrium principle? ANSWER It states that allele and genotype frequencies in a population will remain constant from generation to generation in the absence of evolutionary influences. 90. What is the Hardy-Weinberg equation? ANSWER For a locus with two alleles (A and a), p² + 2pq + q² = 1, where p² is the frequency of AA, 2pq is the frequency of Aa, and q² is the frequency of aa. 91. What are the five conditions required for a population to be in Hardy-Weinberg equilibrium? ANSWER 1. No mutations. 2. Random mating. 3. No natural selection. 4. Extremely large population size (no genetic drift). 5. No gene flow. 92. What is genetic drift? ANSWER Random changes in allele frequencies in a population, especially pronounced in small populations. 93. What is the founder effect? ANSWER A type of genetic drift that occurs when a small group of individuals establishes a new population, whose gene pool is not representative of the source population. Chapter 24: Evolutionary Genetics 94. What is the primary source of new genetic variation in a population? ANSWER Mutation. 95. What is the difference between stabilizing, directional, and disruptive selection? ANSWER Stabilizing selection favors intermediate variants. Directional selection favors one extreme phenotype. Disruptive selection favors both extremes over the intermediate. 96. What is genetic rescue and why is it important in conservation biology? ANSWER It occurs when gene flow from another population introduces new alleles, increasing genetic diversity and fitness in a small, inbred population, reducing extinction risk. Advanced & Synthesis Questions 97. How would you use a Punnett square to predict the outcome of a cross between a homozygous dominant (TT) and a heterozygous (Tt) individual for a tall pea plant trait? ANSWER The cross would be TT x Tt. All offspring would be either TT or Tt, resulting in a 100% tall phenotype. 98. Explain why a man cannot pass an X-linked allele to his son. ANSWER A father contributes his Y chromosome to his sons, not his X chromosome. Therefore, any allele on the father's X chromosome is passed only to his daughters. 99. If a DNA sample has 20% Adenine, what are the percentages of the other three bases? ANSWER If A=20%, then T=20% (Chargaff's rule). This accounts for 40%. The remaining 60% must be G and C, so G=30% and C=30%. 100. Describe how a point mutation in a gene's promoter region might affect gene expression. ANSWER It could increase or decrease the binding affinity of RNA polymerase or transcription factors, thereby altering the rate of transcription and the amount of protein produced, without changing the protein's sequence. 101. A researcher sequences a gene from a patient with a genetic disorder and finds a single base-pair deletion in the first exon. What type of mutation is this, and what is its likely consequence? ANSWER This is a frameshift mutation. It will alter the reading frame from the point of the mutation onward, likely resulting in a completely different and nonfunctional amino acid sequence and a premature stop codon. 102. Why is Taq polymerase used in PCR instead of a human DNA polymerase? ANSWER Taq polymerase is derived from a thermophilic bacterium and is heat-stable, allowing it to withstand the high temperatures (over 90°C) of the PCR denaturation step without being denatured itself. Human DNA polymerases would denature at these temperatures. 103. How does the process of alternative splicing increase proteomic diversity? ANSWER It allows a single pre-mRNA transcript to be spliced in different ways, including or excluding different exons, to produce multiple distinct mRNA isoforms and therefore multiple different proteins from a single gene. 104. In a population genetics study, you observe that the frequency of the homozygous recessive genotype (aa) is 0.09. What is the frequency of the recessive allele (a)? ANSWER The frequency of the aa genotype is q² = 0.09. Therefore, the frequency of the recessive allele (a) is q = √0.09 = 0.3. 105. Explain how a mutation in a tumor suppressor gene like p53 can be dominant at the organismal level but recessive at the cellular level. ANSWER At the cellular level, one functional copy of p53 is usually sufficient for normal function (recessive). However, an individual who inherits one mutated p53 allele (a germline mutation) has a very high risk of cancer because any cell that loses the single remaining functional allele (a somatic mutation) will develop a growth advantage. This makes the predisposition to cancer appear as a dominant trait in a pedigree.