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Biology 30 · Worksheets

Mixed review · Genetics and molecular genetics

Ten questions of mixed difficulty, covering Genetics, Molecular genetics. Print it, or work through it on screen — the answer key starts on its own page.

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Mixed review · Genetics and molecular genetics

Biology 30 · maddyhelps.com

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  1. In eukaryotic cells, what happens to mRNA before it leaves the nucleus?

    1. a) Exons are removed and introns are joined together
    2. b) It is translated into protein
    3. c) Introns are removed and exons are joined together
    4. d) It is copied back into DNA

  2. What causes sickle cell anemia?

    1. a) An extra copy of chromosome 21
    2. b) A single base substitution that changes one amino acid in hemoglobin
    3. c) A missing chromosome
    4. d) A frameshift that deletes the hemoglobin gene

  3. Which tRNA anticodon pairs with the mRNA codon AUG?

    1. a) TAC
    2. b) CAU
    3. c) AUG
    4. d) UAC

  4. How many chromosomes are in a normal human body (somatic) cell?

    1. a) 92
    2. b) 22
    3. c) 46
    4. d) 23

  5. Where does translation happen?

    1. a) at a ribosome
    2. b) in the mitochondria
    3. c) in the nucleus
    4. d) at the cell membrane

  6. Crossing over, which exchanges segments between homologous chromosomes, occurs during:

    1. a) prophase I of meiosis
    2. b) prophase of mitosis
    3. c) interphase
    4. d) metaphase II of meiosis

  7. A father with blood type A (IAi) and a mother with blood type B (IBi) have a child. Which blood types are possible?

    1. a) O only
    2. b) AB only
    3. c) A, B, AB and O
    4. d) A and B only

  8. A permanent change in the sequence of DNA is called a:

    1. a) codon
    2. b) mutation
    3. c) clone
    4. d) chromosome

  9. Tall (T) is dominant over short (t). In the cross Tt × tt, what fraction of the offspring are expected to be tall?

    1. a) 1/4
    2. b) all of them
    3. c) 3/4
    4. d) 1/2

  10. Crossing a red snapdragon (RR) with a white one (WW) produces all pink offspring (RW). This pattern is called:

    1. a) incomplete dominance
    2. b) multiple alleles
    3. c) sex linkage
    4. d) codominance

Answer key · Mixed review · Genetics and molecular genetics

Biology 30 · maddyhelps.com

  1. c) Introns are removed and exons are joined together — Introns are non-coding sections that get cut out; exons, which are expressed, are spliced together into the final message.
  2. b) A single base substitution that changes one amino acid in hemoglobin — One base change swaps one amino acid in hemoglobin. That small change makes red blood cells bend into a sickle shape — a striking example of a missense mutation.
  3. d) UAC — The anticodon is complementary: A–U, U–A, G–C gives UAC. TAC is wrong because RNA uses uracil, not thymine.
  4. c) 46 — Body cells are diploid (2n): 23 pairs, so 46 chromosomes in total. 23 is the haploid number found in a gamete.
  5. a) at a ribosome — Transcription (DNA to mRNA) happens in the nucleus. The mRNA then travels to a ribosome, where it is translated into a protein.
  6. a) prophase I of meiosis — Homologues pair up as tetrads in prophase I, and that pairing is what allows the exchange. It is a major source of genetic variation.
  7. c) A, B, AB and O — Each parent can pass IA, IB or i, giving IAIB (AB), IAi (A), IBi (B) and ii (O) — all four types, each with probability 1/4.
  8. b) mutation — Mutations can be harmful, helpful or have no effect at all. They are the original source of all new alleles.
  9. d) 1/2 — The Punnett square gives Tt, Tt, tt, tt — half carry a T and are tall. This 1:1 result is the classic testcross pattern.
  10. a) incomplete dominance — Incomplete dominance blends the two into an intermediate phenotype. Codominance would show both colours fully, as in a red-and-white patched flower.