Molecular Biology & Genetics – Final Exam Review

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A comprehensive set of 97 question-and-answer flashcards covering key concepts in molecular biology and genetics for final exam preparation.

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383 Terms

1
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What is an allele in genetics?

A specific version or variant of a gene (e.g., brown vs. blue eye‐color allele).

2
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What does the term locus refer to?

The physical location of a gene on a chromosome.

3
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What are homologous chromosomes?

A pair of chromosomes, one from each parent, that carry the same genes at the same loci.

4
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What is the centromere?

The constricted region that joins sister chromatids and attaches to spindle fibers during division.

5
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What is a telomere?

The protective end region of a chromosome that prevents degradation and fusion.

6
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Define genotype.

The genetic makeup of an organism, usually written as allele pairs (e.g., AA, Aa, aa).

7
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Define phenotype.

The observable physical or biochemical traits produced by the genotype (e.g., blue eyes, tall height).

8
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What is a dominant allele?

An allele that expresses its phenotype even when only one copy is present (heterozygous condition).

9
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What is a recessive allele?

An allele that is expressed only when two copies are present (homozygous condition).

10
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What is codominance?

A pattern where both alleles in a heterozygote are fully expressed (e.g., AB blood type).

11
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What is incomplete dominance?

A pattern where the heterozygote displays an intermediate, blended phenotype (e.g., pink flowers).

12
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What is pleiotropy?

A situation where one gene influences multiple, seemingly unrelated traits.

13
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What does homozygous mean?

Having two identical alleles for a particular gene (AA or aa).

14
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What does heterozygous mean?

Having two different alleles for a particular gene (Aa).

15
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In a monohybrid cross of Aa × Aa, what is the expected genotype ratio?

1 AA : 2 Aa : 1 aa.

16
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In an Aa × Aa cross where A is dominant, what is the phenotype ratio?

3 dominant trait : 1 recessive trait.

17
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What is the typical phenotype ratio for a dihybrid cross (AaBb × AaBb)?

9 : 3 : 3 : 1.

18
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Why is a test cross performed?

To determine the unknown genotype of an organism showing a dominant phenotype by crossing it with a homozygous recessive individual.

19
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If a test cross yields all dominant offspring, what is the unknown parent's genotype?

Homozygous dominant (AA).

20
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Why do X-linked recessive traits appear more often in males than females?

Males have only one X chromosome, so a single recessive allele is expressed, whereas females need two copies.

21
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What pedigree clue suggests an autosomal dominant inheritance?

The trait appears in every generation and affects both sexes equally.

22
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What pedigree clue suggests an autosomal recessive inheritance?

The trait can skip generations and often appears among siblings of unaffected parents (carriers).

23
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What pedigree clue indicates X-linked recessive inheritance?

More males are affected and there is no male-to-male transmission of the trait.

24
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Who transmits mitochondrial (mtDNA) disorders to offspring?

Only mothers pass mitochondrial DNA to all their children.

25
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Give an example of labile (constantly dividing) cells.

Epidermal skin cells, GI tract lining, or bone-marrow cells.

26
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Give an example of stable (quiescent) cells.

Hepatocytes (liver), renal tubule cells, or smooth muscle cells that divide after injury.

27
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Give an example of permanent (non-dividing) cells.

Neurons, cardiac muscle cells, and skeletal muscle cells.

28
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Name the three stages of interphase.

G₁ (growth), S (DNA synthesis), and G₂ (preparation for mitosis).

29
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What key event occurs during S phase?

DNA replication that doubles each chromosome into two sister chromatids.

30
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What happens during G₂ phase?

The cell checks DNA for errors and prepares proteins needed for mitosis.

31
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What is the primary purpose of mitosis?

To produce two genetically identical diploid cells for growth and tissue repair.

32
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How many chromosomes does a human cell have just before mitosis?

46 chromosomes (as duplicated sister chromatids).

33
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After mitosis, how many cells and chromosomes result?

Two cells, each with 46 chromosomes (diploid).

34
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What is the primary purpose of meiosis?

To create four genetically unique haploid gametes for sexual reproduction.

35
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How many cells and what ploidy result after meiosis II?

Four non-identical haploid cells, each with 23 chromosomes.

36
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During which substage of meiosis does crossing-over occur?

Prophase I (specifically the pachytene stage).

37
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What separates in anaphase I versus anaphase II of meiosis?

Anaphase I separates homologous chromosome pairs; anaphase II separates sister chromatids.

38
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Define euploidy.

Having the normal, complete set of chromosomes for the species (e.g., 46 in humans).

39
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Define aneuploidy.

Having an abnormal number of chromosomes (e.g., 45 or 47).

40
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Turner syndrome (45,X) is an example of which chromosomal abnormality?

Monosomy—missing one chromosome of a pair.

41
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Down syndrome (47, +21) is an example of which abnormality?

Trisomy—three copies of chromosome 21.

42
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What is a Robertsonian translocation?

Fusion of two acrocentric chromosomes at their centromeres, forming one large chromosome and a tiny fragment.

43
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Which chromosomes are most often involved in Robertsonian translocations?

Acrocentric chromosomes 13, 14, 15, 21, and 22.

44
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What is the most common cause of Down syndrome?

Nondisjunction during meiosis leading to trisomy 21.

45
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Which hand feature is classic for Down syndrome?

A single palmar (Simian) crease.

46
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What is the typical survival outlook for infants with Edwards syndrome (trisomy 18)?

Most affected infants die within the first year of life.

47
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Polydactyly is characteristic of which trisomy?

Patau syndrome (trisomy 13).

48
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What is the normal male karyotype?

46, XY.

49
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What is the function of the SRY gene?

It encodes testis-determining factor, initiating male sexual development.

50
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What adult structures are derived from the mesonephric (Wolffian) duct?

Epididymis, vas deferens, seminal vesicles, and ejaculatory ducts (mnemonic: SEED).

51
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What structures arise from the paramesonephric (Müllerian) duct?

Fallopian tubes, uterus, cervix, and upper one-third of the vagina.

52
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How many Barr bodies are present in a normal female (46,XX) cell?

One inactive X chromosome, visible as a Barr body.

53
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What is the genotype for Klinefelter syndrome?

47, XXY.

54
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Which cancer risk is higher in Klinefelter patients?

Breast cancer (and some germ-cell tumors).

55
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What is the genotype for Turner syndrome?

45, X (monosomy X).

56
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Which classic heart defect is associated with Turner syndrome?

Coarctation of the aorta (also bicuspid aortic valve).

57
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How is mitochondrial DNA inherited?

Exclusively from the mother (maternal inheritance).

58
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Which sugar is found in RNA nucleotides?

Ribose.

59
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How many hydrogen bonds connect A–T and C–G base pairs?

A–T has 2 bonds; C–G has 3 bonds.

60
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Which bases are purines?

Adenine (A) and Guanine (G).

61
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State the central dogma of molecular biology.

Information flows from DNA → RNA → Protein.

62
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What is the main role of DNA polymerase III?

It adds nucleotides to the growing DNA strand in the 5′→3′ direction during replication.

63
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What is the function of DNA ligase?

It seals nicks and joins Okazaki fragments on the lagging strand.

64
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What does topoisomerase do during replication?

Relieves supercoiling ahead of the replication fork by cutting and re-rejoining DNA.

65
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In which cell types is telomerase highly active?

Germ cells, stem cells, and most cancer cells.

66
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Which strand is synthesized continuously toward the replication fork?

The leading strand.

67
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How do origins of replication differ in prokaryotes versus eukaryotes?

Prokaryotes have one origin per chromosome; eukaryotes have multiple origins per chromosome.

68
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What forms the core of a nucleosome?

An octamer of histone proteins (2 each of H2A, H2B, H3, and H4) wrapped by DNA.

69
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Which type of chromatin is transcriptionally active?

Euchromatin (loosely packed, light-staining).

70
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What is the function of the TATA box within a promoter?

It is a DNA sequence where transcription factors and RNA polymerase II assemble to start transcription.

71
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What is the purpose of the 5′ m⁷G cap on eukaryotic mRNA?

Protects mRNA from degradation and aids ribosome binding for translation initiation.

72
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What does RNA splicing remove from pre-mRNA?

Introns (non-coding sequences).

73
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What three-letter codon serves as the universal start codon?

AUG (codes for methionine).

74
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Name the three stop codons.

UAA, UAG, and UGA.

75
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What is the role of the anticodon on tRNA?

It base-pairs with the complementary mRNA codon to ensure correct amino acid incorporation.

76
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Where does translation occur in eukaryotic cells?

In the cytoplasm, on free ribosomes or ribosomes bound to rough endoplasmic reticulum.

77
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What are Okazaki fragments?

Short DNA segments synthesized discontinuously on the lagging strand during replication.

78
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What type of error is corrected by mismatch repair?

Incorrectly paired bases inserted during DNA replication.

79
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What is the consequence of a nonsense mutation?

A premature stop codon, leading to a truncated, usually nonfunctional protein.

80
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Which disease is commonly caused by a ΔF508 mutation in the CFTR gene?

Cystic fibrosis.

81
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Which disease results from a Glu→Val substitution in β-globin?

Sickle cell anemia.

82
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Expansion of CAG repeats causes which neurodegenerative disorder?

Huntington’s disease.

83
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Loss of the paternal copy of chromosome 15 results in which syndrome?

Prader-Willi syndrome.

84
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Bilateral vestibular schwannomas are diagnostic of which condition?

Neurofibromatosis type 2 (NF2).

85
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What is the inheritance pattern of cystic fibrosis?

Autosomal recessive.

86
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Why are sickle-cell carriers relatively protected from malaria?

Heterozygous (AS) red cells impede the life cycle of Plasmodium parasites.

87
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Carcinomas originate from which basic tissue type?

Epithelial tissues (coverings and linings).

88
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How does a gain-of-function mutation in an oncogene promote cancer?

It keeps cellular growth signals permanently activated (accelerator stuck on).

89
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What is a driver mutation?

A genetic alteration that directly contributes to cancer initiation and progression.

90
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During PCR, at approximately what temperature does DNA denaturation occur?

Around 95 °C to separate the DNA strands.

91
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Why is Taq polymerase used in PCR?

It is heat-stable and remains active after repeated high-temperature cycles.

92
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In gel electrophoresis, which DNA fragments migrate farthest?

The smallest (shortest) fragments travel the greatest distance through the gel.

93
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What is the purpose of a DNA ladder in gel electrophoresis?

It provides fragment size markers for estimating the lengths of sample DNA bands.

94
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In DNA fingerprinting, child bands that do not match the mother must come from whom?

The biological father.

95
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List the three basic steps of one PCR cycle in order.

Denaturation → Annealing → Extension.

96
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Which enzyme synthesizes RNA during transcription in eukaryotes?

RNA polymerase II (for mRNA).

97
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What is the function of the 3′ poly-A tail on mRNA?

Enhances mRNA stability, aids nuclear export, and assists in translation termination.

98
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What is an allele in genetics?

A specific version or variant of a gene (e.g., brown vs. blue eye‐color allele).

99
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What does the term locus refer to?

The physical location of a gene on a chromosome.

100
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What are homologous chromosomes?

A pair of chromosomes, one from each parent, that carry the same genes at the same loci.