Genetics and Heredity Quiz

Grade 10 · Science · Quiz

Test your knowledge of Mendelian genetics, Punnett squares, inheritance patterns, and genetic vocabulary.

Questions

1. What does it mean when an organism is described as heterozygous?

   1. It has two identical alleles
   2. It has two different alleles for a gene
   3. It expresses a recessive trait
   4. It has an extra chromosome
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   Answer: It has two different alleles for a gene

   Heterozygous (e.g., Tt) means the organism carries one dominant and one recessive allele for a particular gene — they are different from each other.

2. In a monohybrid cross of Tt × Tt, 75% of offspring will display the dominant phenotype.

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   Answer: True

   Tt × Tt Punnett square gives: TT (25%), Tt (50%), tt (25%). Genotypes TT and Tt both display the dominant phenotype = 75%. Only tt (25%) displays recessive.

3. Blood type AB in humans is an example of:

   1. Incomplete dominance
   2. Codominance
   3. Simple dominance
   4. Sex linkage
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   Answer: Codominance

   In blood type AB, both the A and B alleles are fully expressed simultaneously — a person has both A and B antigens on their red blood cells. Neither masks the other.

4. Mendel's Law of ___ states that alleles separate from each other during gamete formation.

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   Answer: Segregation

   Mendel's Law of Segregation: during gamete formation (meiosis), the two alleles for a gene separate so that each gamete receives only one allele.

5. A red flower (RR) is crossed with a white flower (WW) showing incomplete dominance. What color will all F1 offspring be?

   1. Red
   2. White
   3. Pink
   4. Spotted red and white
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   Answer: Pink

   In incomplete dominance, the F1 heterozygotes (RW) show an intermediate phenotype. Neither allele is fully dominant — the result is pink, a blend of red and white.

6. A carrier of a recessive genetic disease has the disease phenotype.

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   Answer: False

   A carrier is heterozygous (e.g., Aa) — they have one copy of the recessive disease allele but one dominant allele masks it. Carriers do not have the disease phenotype but can pass the allele to offspring.

7. Which genotype represents a homozygous recessive individual?

   1. TT
   2. Tt
   3. tT
   4. tt
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   Answer: tt

   Homozygous recessive means both alleles are the lowercase (recessive) form. Only tt individuals express the recessive phenotype.

8. Traits controlled by many genes acting together are described as ___ traits.

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   Answer: polygenic

   Polygenic traits (like height, skin color, eye color in humans) are controlled by two or more genes acting together, producing a continuous range of phenotypes.

9. Males (XY) are more likely to express X-linked recessive traits than females (XX).

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   Answer: True

   Males have one X chromosome (XY). If their single X carries a recessive allele, they will express the trait (no second X to mask it). Females need two copies (XX) to express X-linked recessive traits.

10. In a test cross, a plant with an unknown genotype is crossed with a:

    1. Heterozygous plant
    2. Homozygous dominant plant
    3. Homozygous recessive plant
    4. Plant with the same phenotype
    Show answer

    Answer: Homozygous recessive plant

    A test cross uses a homozygous recessive (tt) individual. If the unknown plant is homozygous dominant (TT), all offspring are tall (Tt). If heterozygous (Tt), offspring are 50% tall and 50% short — revealing the unknown genotype.

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