Practice quiz · by a Quizcard user

AP Biology: Genetics and Heredity — quiz

18 multiple-choice questions covering DNA/RNA base pairing, Frameshift mutations, Point mutations, Translation, DNA replication. One answer each; you get a score at the end and the explanation for every question. No account needed.

Updated 2026-10-24. Keys 1–4 pick an answer, Enter moves on. Redo it any time, in order or shuffled.

The questions

Answers and explanations are shown after you finish.

1. DNA/RNA base pairing

   A DNA template strand reads 3'-TACGGA-5'. What mRNA sequence would be transcribed from it?

   • 5'-AUGCCT-3'
   • 5'-ATGCCT-3'
   • 5'-UACGGA-3'
   • 5'-AUGCCU-3'
2. Frameshift mutations

   A single nucleotide is deleted near the beginning of a gene's coding sequence. What is the most likely effect on the resulting protein?

   • A premature stop codon appears immediately at the deletion site only
   • A shift in the reading frame scrambles most of the downstream amino acid sequence
   • A single amino acid is swapped for another, but the protein still works
   • No change, because the deletion is outside the gene
3. Point mutations

   A point mutation changes the codon UAC (tyrosine) into UAA. What type of mutation is this?

   • Nonsense mutation
   • Silent mutation
   • Missense mutation
   • Frameshift mutation
4. Translation

   During translation, what directly signals the ribosome to release the finished polypeptide?

   • The ribosome reaching the 5' cap of the mRNA
   • A tRNA bringing a stop amino acid
   • The ribosome encountering a stop codon such as UAA
   • The poly-A tail binding the ribosome
5. DNA replication

   On the lagging strand, DNA is synthesized in short Okazaki fragments. Which enzyme seals the gaps between these fragments into a continuous strand?

   • Primase
   • Helicase
   • DNA ligase
   • DNA polymerase
6. CRISPR-Cas9

   In CRISPR-Cas9 gene editing, what role does the guide RNA play?

   • It serves as a primer that DNA polymerase extends
   • It is translated into the Cas9 protein itself
   • It repairs the DNA break after Cas9 cuts it
   • It directs the Cas9 enzyme to the specific DNA sequence to be cut
7. Gel electrophoresis

   A researcher runs a gel with DNA fragments of 200 bp, 500 bp, and 1000 bp. Which fragment migrates farthest toward the positive electrode?

   • The 200 bp fragment, because smaller fragments move faster through the gel
   • The 500 bp fragment, because it is intermediate in size
   • All fragments move the same distance since DNA charge density is constant
   • The 1000 bp fragment, because it has more charge
8. Epigenetics

   Identical twins share the same DNA sequence, yet one develops a disease linked to a silenced tumor-suppressor gene while the other does not. What best explains this difference?

   • The twins actually have different alleles at that locus
   • Epigenetic changes such as DNA methylation altered gene expression without changing the sequence
   • Differences in mRNA codon usage changed the protein produced
   • One twin has a unique mutation the other lacks
9. Lac operon regulation

   In E. coli, both lactose and glucose are present in high amounts. Compared to when lactose is present but glucose is absent, lac operon transcription will be...

   • Lower, because low cAMP means CAP cannot strongly activate the promoter
   • Unaffected, since glucose has no influence on the lac operon
   • Higher, because both sugars together maximize activation
   • Completely shut off by the lac repressor
10. Test crosses

    A purple-flowered pea plant is crossed with a white-flowered plant, and the offspring are 50% purple and 50% white. What does this reveal about the purple parent's genotype?

    • It is homozygous dominant (PP)
    • It is homozygous recessive (pp)
    • Its genotype cannot be determined from this cross
    • It is heterozygous (Pp)
11. Independent assortment

    Two pea plants, each heterozygous for seed shape and seed color (RrYy), are crossed. Assuming independent assortment, what phenotypic ratio is expected in the offspring?

    • 1:2:1
    • 3:1
    • 9:3:3:1
    • 1:1:1:1
12. Genotype vs phenotype

    Two pea plants both display red flowers, but one has genotype RR and the other has genotype Rr. This best illustrates that...

    • Different genotypes can produce the same phenotype
    • Incomplete dominance is occurring
    • The red allele is recessive
    • Phenotype always reveals the exact genotype
13. Nondisjunction

    A gamete is found to contain 24 chromosomes instead of the normal 23 because a homologous pair failed to separate during meiosis I. This error is called...

    • Polyploidy
    • Crossing over
    • Nondisjunction
    • Translocation
14. Sex-linked inheritance

    A woman who is an unaffected carrier for an X-linked recessive disorder has sons with a 50% chance of being affected, while her daughters are rarely affected. Why are sons at higher risk?

    • The Y chromosome carries a dominant allele that worsens the disorder
    • Males have two copies of the gene, doubling their risk
    • Daughters inherit the disorder only from their father
    • Males have only one X chromosome, so a single recessive allele is expressed
15. X-inactivation / Barr bodies

    Calico cats display patches of orange and black fur. This pattern is best explained by which process?

    • Two separate genes controlling fur color on different chromosomes
    • Environmental temperature affecting pigment genes during development
    • Incomplete dominance blending orange and black pigments
    • Random inactivation of one X chromosome in each cell, forming a Barr body
16. Epistasis

    In Labrador retrievers, dogs with genotype ee are yellow regardless of whether their B gene would otherwise produce black or brown pigment. This relationship between the E and B genes is an example of...

    • Incomplete dominance
    • Pleiotropy
    • Epistasis
    • Codominance
17. Codominance vs incomplete dominance

    Which scenario best demonstrates codominance rather than incomplete dominance?

    • A red snapdragon crossed with a white one produces pink offspring
    • A heterozygous pea plant shows a blended intermediate seed color
    • Mixing two paint colors produces a new, uniform shade
    • A person with genotype IAIB has both A and B antigens fully expressed on their red blood cells
18. Pleiotropy

    The sickle cell allele changes red blood cell shape, affects oxygen-carrying capacity, and also provides some resistance to malaria. This wide-ranging effect of a single gene is called...

    • Polygenic inheritance
    • Epistasis
    • Codominance
    • Pleiotropy