Genetics and Heredity Quiz

Grade 9 · Science · Quiz

Test your knowledge of inheritance patterns, Punnett squares, and Mendel's laws with 10 questions.

Questions

  1. An organism with genotype BB is:

    1. Heterozygous dominant
    2. Homozygous dominant
    3. Homozygous recessive
    4. Codominant
    Show answer

    Answer: Homozygous dominant

    BB has two identical dominant alleles — that is homozygous dominant. Bb would be heterozygous; bb would be homozygous recessive.

  2. In incomplete dominance, neither allele is dominant over the other and a blended phenotype results.

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    Answer: True

    Incomplete dominance produces an intermediate phenotype — neither allele is completely dominant. Classic example: red (RR) × white (WW) snapdragons produce pink (RW) offspring.

  3. Gregor Mendel conducted his famous inheritance experiments using ___ plants.

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    Answer: pea

    Mendel chose pea plants (Pisum sativum) for their distinct, easily observable traits (tall/short, smooth/wrinkled seeds) and short generation time. He studied 7 traits across thousands of plants.

  4. A cross between a homozygous dominant (TT) and homozygous recessive (tt) plant produces offspring that are all:

    1. TT
    2. tt
    3. Tt
    4. 50% TT and 50% tt
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    Answer: Tt

    TT × tt: every offspring gets one T from the dominant parent and one t from the recessive parent — all offspring are Tt (heterozygous), all showing the dominant tall phenotype.

  5. Which blood type demonstrates codominance?

    1. Type A
    2. Type O
    3. Type AB
    4. Type B
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    Answer: Type AB

    Blood type AB demonstrates codominance — both the A allele (makes A antigens) and the B allele (makes B antigens) are fully expressed simultaneously. Neither dominates the other.

  6. The Law of Independent Assortment states that genes on the same chromosome always assort independently.

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    Answer: False

    The Law of Independent Assortment applies to genes on DIFFERENT chromosomes. Genes on the same chromosome tend to be inherited together (linked genes) and do NOT assort independently.

  7. If B = black fur (dominant) and b = white fur (recessive), what is the phenotype of a Bb rabbit?

    1. White
    2. Black
    3. Gray (blend)
    4. Spotted
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    Answer: Black

    With complete dominance, one B allele is sufficient to produce black fur. The recessive b allele is masked. Only bb rabbits would have white fur.

  8. The specific location of a gene on a chromosome is called its ___.

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    Answer: locus

    A locus (plural: loci) is the specific fixed position on a chromosome where a gene is located. Alleles of the same gene are found at the same locus on homologous chromosomes.

  9. In a Tt × tt cross, what is the expected phenotype ratio?

    1. All tall
    2. 3 tall : 1 short
    3. 1 tall : 1 short
    4. All short
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    Answer: 1 tall : 1 short

    Tt × tt Punnett square: Tt, Tt, tt, tt = 50% Tt (tall) and 50% tt (short). This 1:1 ratio is the hallmark of a testcross used to determine an unknown genotype.

  10. Which term describes an organism's genetic makeup?

    1. Phenotype
    2. Genotype
    3. Karyotype
    4. Allele
    Show answer

    Answer: Genotype

    Genotype is the genetic code (e.g., Tt, AABB). Phenotype is what you can see. Karyotype is a picture of all chromosomes. Allele is one version of a gene.

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