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Biology 30 · Worksheets

Genetics · Set B

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

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Genetics · Set B

Biology 30 · maddyhelps.com

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Circle the best answer for each question. Show your work in the space provided.

  1. In pea plants, tall (T) is dominant over short (t). A plant with the genotype Tt will be:

    1. a) short
    2. b) tall
    3. c) impossible to predict
    4. d) medium height

  2. In the cross AaBb × aaBb, what fraction of the offspring are expected to have the genotype aaBB?

    1. a) 1/4
    2. b) 1/8
    3. c) 3/8
    4. d) 1/16

  3. An organism with two identical alleles for a trait is described as:

    1. a) homozygous
    2. b) polygenic
    3. c) heterozygous
    4. d) hybrid

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

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

  5. During which stage do homologous chromosomes separate from each other?

    1. a) anaphase II of meiosis
    2. b) anaphase I of meiosis
    3. c) telophase I of meiosis
    4. d) anaphase of mitosis

  6. A DNA template strand reads TAC. What is the matching mRNA codon?

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

  7. 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) codominance
    3. c) multiple alleles
    4. d) sex linkage

  8. Which enzyme unwinds and separates the two strands of DNA during replication?

    1. a) helicase
    2. b) RNA polymerase
    3. c) DNA polymerase
    4. d) ligase

  9. A DNA template strand reads 3′-TAC GGC TAA-5′. How many amino acids will the resulting polypeptide contain?

    1. a) 9
    2. b) 3
    3. c) 2
    4. d) 6

  10. One parent cell going through meiosis produces how many daughter cells?

    1. a) 8
    2. b) 2
    3. c) 1
    4. d) 4

Answer key · Genetics · Set B

Biology 30 · maddyhelps.com

  1. b) tall — One dominant allele is enough to show the dominant trait, so Tt is tall. Only tt, with no dominant allele, is short.
  2. b) 1/8 — Handle each gene separately, then multiply: Aa × aa gives 1/2 aa, and Bb × Bb gives 1/4 BB. So 1/2 × 1/4 = 1/8.
  3. a) homozygous — Homo- means same, so TT and tt are both homozygous. Heterozygous (Tt) means the two alleles differ.
  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. b) anaphase I of meiosis — Anaphase I pulls whole homologous pairs apart, which is what halves the chromosome number. Sister chromatids separate later, in anaphase II.
  6. d) AUG — Transcription pairs T→A, A→U, C→G, giving AUG. RNA never uses thymine, which rules out ATG.
  7. 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.
  8. a) helicase — Helicase breaks the hydrogen bonds to open the helix. DNA polymerase then builds the new strands, and ligase seals the gaps between fragments.
  9. b) 3 — The mRNA is 5′-AUG CCG AUU-3′, which is 3 codons, and each codon codes for one amino acid. Nine bases ÷ 3 bases per codon = 3.
  10. d) 4 — Meiosis has two divisions, so one cell becomes 4. Mitosis has only one division and produces 2.