Genetics and Heredity Quiz

Grade 7 · Science · Quiz

10-question quiz on genes, alleles, Punnett squares, and Mendelian genetics.

Questions

1. What are the different forms of a gene called?

   1. Chromosomes
   2. Alleles
   3. Phenotypes
   4. Mutations
   Show answer

   Answer: Alleles

   Alleles are the different versions of a gene (like blue vs. brown for eye color genes).

2. A genotype of BB is heterozygous.

   Show answer

   Answer: False

   BB has two identical dominant alleles, making it homozygous dominant, not heterozygous.

3. An organism that has two of the same alleles (like TT or tt) is said to be ___.

   Show answer

   Answer: homozygous

   Homozygous means both alleles for a given gene are the same — either both dominant or both recessive.

4. If brown eyes (B) are dominant over blue eyes (b), what eye color would a person with genotype Bb have?

   1. Blue
   2. Green
   3. Brown
   4. A mixture of both
   Show answer

   Answer: Brown

   Brown (B) is dominant, so even one copy is enough to produce brown eyes. Bb expresses the dominant phenotype (brown).

5. Dominant alleles are always more common in a population than recessive alleles.

   Show answer

   Answer: False

   Dominance refers to expression, not frequency. Recessive alleles can be very common in a population (e.g., blood type O).

6. How many chromosomes are in a typical human body cell?

   1. 23
   2. 46
   3. 64
   4. 92
   Show answer

   Answer: 46

   Human body cells are diploid (2n = 46), containing 23 chromosome pairs — one set from each parent.

7. The genetic makeup of an organism is called its ___.

   Show answer

   Answer: genotype

   Genotype is the actual set of alleles an organism carries, regardless of which are expressed.

8. Mendel's Law of Segregation states that:

   1. Genes are located on chromosomes
   2. Dominant alleles always appear first
   3. Each parent passes one allele per gene to offspring
   4. Traits are blended in offspring
   Show answer

   Answer: Each parent passes one allele per gene to offspring

   The Law of Segregation means allele pairs separate during meiosis so each gamete carries only one allele per gene.

9. In codominance, both alleles are fully expressed in the offspring.

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   Answer: True

   In codominance, neither allele is dominant. Both are fully expressed simultaneously (e.g., roan cattle showing both red and white hairs).

10. In a cross between two heterozygous parents (Tt × Tt), what percentage of offspring will show the dominant phenotype?

    1. 25%
    2. 50%
    3. 75%
    4. 100%
    Show answer

    Answer: 75%

    Tt × Tt produces TT (25%), Tt (50%), and tt (25%). TT and Tt both show dominant phenotype = 75%.

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