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Quiz: Meiosis and Mendelian Genetics

Test your understanding of meiotic divisions, sources of genetic variation, and Mendel's laws of inheritance with these review questions.

1. What is the diploid chromosome number in humans, and how many chromosomes are found in a human gamete?

  1. 23 diploid; 46 haploid
  2. 46 diploid; 46 haploid
  3. 46 diploid; 23 haploid
  4. 23 diploid; 23 haploid
Show Answer

The correct answer is C. Human somatic cells are diploid (2n = 46), carrying two complete sets of 23 chromosomes, one from each parent. Meiosis reduces this to the haploid number (n = 23) in gametes, so that fertilization of two haploid gametes restores the diploid number in the resulting zygote.

Concept Tested: Haploid and diploid chromosome numbers

2. According to Mendel's Law of Segregation, what happens to the two alleles for a gene during gamete formation?

  1. The two alleles separate from each other so that each gamete receives only one allele for that gene
  2. The two alleles combine into a single fused allele in every gamete
  3. Both alleles are duplicated and passed into every gamete
  4. One allele is destroyed while the other is duplicated
Show Answer

The correct answer is A. The Law of Segregation states that the two alleles an individual carries for a gene separate during gamete formation, so each gamete receives only one of the two alleles. This directly mirrors the physical separation of homologous chromosomes during anaphase I of meiosis, which carry those alleles apart from each other.

Concept Tested: Mendel's Law of Segregation

3. Why does crossing over during prophase I increase genetic diversity among gametes?

  1. It duplicates entire chromosomes before meiosis begins
  2. It causes homologous chromosomes to separate randomly at anaphase I
  3. It fuses maternal and paternal chromosomes into a single chromosome
  4. It exchanges DNA segments between non-sister chromatids of homologous chromosomes, creating chromatids with new combinations of maternal and paternal alleles
Show Answer

The correct answer is D. During crossing over, non-sister chromatids of homologous chromosomes exchange segments of DNA at points called chiasmata. This produces recombinant chromatids that carry a mixture of maternal and paternal alleles along a single chromosome, generating allele combinations that did not exist in either parent chromosome before recombination.

Concept Tested: Crossing over and genetic recombination

4. How does anaphase I of meiosis differ from anaphase of mitosis?

  1. In anaphase I, sister chromatids separate exactly as they do in mitotic anaphase
  2. In anaphase I, homologous chromosomes separate while sister chromatids remain joined, whereas in mitotic anaphase sister chromatids themselves separate
  3. In anaphase I, no chromosome movement occurs at all
  4. In anaphase I, four haploid cells are produced directly
Show Answer

The correct answer is B. In anaphase I, whole homologous chromosomes (each still composed of two sister chromatids) separate and move to opposite poles, reducing the chromosome number to haploid. This contrasts with mitotic anaphase, where sister chromatids themselves separate to become individual chromosomes, keeping the chromosome number the same in each daughter cell.

Concept Tested: Meiosis I vs. mitosis

5. Why does a cross between two heterozygotes (Aa × Aa) produce a 3:1 phenotypic ratio rather than a 2:1 ratio?

  1. Because two of the four Punnett square outcomes are always lethal
  2. Because homozygous dominant offspring are twice as likely to survive
  3. Because independent assortment eliminates one recessive class
  4. Because both AA and Aa genotypes produce the identical dominant phenotype, making the dominant class 3 of the 4 total offspring (1 AA + 2 Aa)
Show Answer

The correct answer is D. The Punnett square for Aa × Aa yields a 1:2:1 genotypic ratio of AA:Aa:aa. Because AA and Aa are phenotypically indistinguishable (both display the dominant trait), these two classes combine into a single dominant phenotypic category representing 3 of the 4 total offspring, yielding the classic 3:1 phenotypic ratio.

Concept Tested: Monohybrid cross ratios

6. A diploid organism has 2n = 8. How many chromosomes will be present in each of its gametes, and how many genetically distinct gamete types are possible through independent assortment alone?

  1. 4 chromosomes per gamete; 16 distinct gamete types
  2. 8 chromosomes per gamete; 8 distinct gamete types
  3. 4 chromosomes per gamete; 8 distinct gamete types
  4. 8 chromosomes per gamete; 16 distinct gamete types
Show Answer

The correct answer is A. With 2n = 8, the haploid number is n = 4 chromosomes per gamete. Independent assortment allows each of the 4 homologous pairs to orient randomly at metaphase I, giving 2^4 = 16 possible combinations of maternal and paternal chromosomes in the resulting gametes, not counting the additional variation from crossing over.

Concept Tested: Independent assortment and gamete diversity

7. In pea plants, round seed shape (R) is dominant over wrinkled (r). Two heterozygous (Rr) plants are crossed. What fraction of the offspring is expected to have wrinkled seeds?

  1. 1/2
  2. 1/16
  3. 1/4
  4. 3/4
Show Answer

The correct answer is C. Crossing Rr × Rr produces a genotypic ratio of 1 RR : 2 Rr : 1 rr. Since wrinkled seeds require the homozygous recessive genotype (rr), and only 1 of the 4 possible offspring genotypes is rr, the expected fraction with wrinkled seeds is 1/4, corresponding to the recessive portion of the classic 3:1 phenotypic ratio.

Concept Tested: Punnett squares and monohybrid cross calculations

8. A plant of unknown genotype showing the dominant tall phenotype is crossed with a homozygous recessive short plant. The offspring appear in a 1:1 ratio of tall to short. What is the genotype of the unknown parent?

  1. Homozygous dominant (TT)
  2. Heterozygous (Tt)
  3. Homozygous recessive (tt)
  4. Cannot be determined from this cross
Show Answer

The correct answer is B. This is a test cross: crossing an unknown genotype with a homozygous recessive individual reveals the unknown's genotype through the offspring ratio. If the unknown were homozygous dominant (TT), all offspring would be tall. A 1:1 ratio of tall to short offspring indicates the unknown parent is heterozygous (Tt), producing T and t gametes in equal proportions.

Concept Tested: Test crosses

9. A dihybrid cross of RrYy × RrYy produces offspring with far more parental-type combinations (round yellow and wrinkled green) than expected recombinant types, deviating significantly from the predicted 9:3:3:1 ratio. What does this deviation most likely indicate?

  1. The two genes are likely linked on the same chromosome and do not assort independently, unlike genes on separate chromosomes
  2. The cross was performed incorrectly and should be repeated
  3. The dominant alleles are lethal in combination
  4. Crossing over did not occur during meiosis in either parent
Show Answer

The correct answer is A. The 9:3:3:1 ratio assumes the two genes assort independently because they lie on different chromosomes. When two genes are physically linked on the same chromosome, they tend to be inherited together more often than predicted by independent assortment, producing an excess of parental-type combinations and a deficit of recombinant types — a deviation that signals genetic linkage rather than experimental error.

Concept Tested: Independent assortment and genetic linkage

10. How do crossing over and independent assortment differ in the genetic variation they generate during meiosis?

  1. Both mechanisms produce the identical genetic outcome and are functionally redundant
  2. Independent assortment creates new allele combinations within a single chromosome, while crossing over shuffles entire chromosomes between gametes
  3. Neither mechanism contributes to genetic variation; only random fertilization does
  4. Crossing over creates new allele combinations within a single chromosome by exchanging segments between homologs, while independent assortment shuffles whole, intact maternal and paternal chromosomes between gametes without altering the alleles within any one chromosome
Show Answer

The correct answer is D. Crossing over physically exchanges DNA segments between non-sister chromatids of homologous chromosomes, producing recombinant chromosomes with new allele combinations along their length. Independent assortment, by contrast, does not alter the allele composition of any single chromosome; it simply randomizes which intact maternal or paternal chromosome from each homologous pair ends up in a given gamete.

Concept Tested: Sources of genetic variation in meiosis