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5.2 Meiosis and Genetic Diversity

Syllabus
2025
Topic
5.2
Level
—

Learning objectives

5.2A—Explain how the process of meiosis generates genetic diversityExplain how the process of meiosis generates genetic diversity.• Correct separation of the homologous chromosomes in meiosis I and sister chromatids in meiosis II ensures that each gamete receives a haploid (1n) set of chromosomes that comprises an assortment of both maternal and paternal chromosomes. When incorrect separation occurs (nondisjunction), gametes are no longer haploid.• During prophase I of meiosis, non-sister chromatids exchange genetic material via a process called crossing over (recombination), which increases genetic diversity among the resultant gametes.• Sexual reproduction in eukaryotes increases genetic variation, including crossing over, random assortment of chromosomes during meiosis, and subsequent fertilization of gametes.- Exclusion: Knowledge of the details of sexual reproduction cycles in various plants and animals is beyond the scope of the AP Exam.

How Meiosis and Fertilization Generate Genetic Diversity

Sexual reproduction generates genetic diversity by reshuffling existing alleles into new chromosome and gamete combinations. Crossing over acts within homologous pairs, random assortment distributes whole maternal and paternal chromosomes, and fertilization combines two independently produced gametes.

Mechanism When it acts How it changes genetic combinations
Crossing over (recombination) Prophase I Non-sister chromatids of homologous chromosomes exchange corresponding DNA segments, producing recombinant chromatids
Random assortment Homologous pairs align and separate in meiosis I Each gamete receives a random mixture of maternal and paternal homologs
Fertilization After meiosis One gamete combines with another, joining two independently assembled haploid chromosome sets

Correct separation of homologs in meiosis I and sister chromatids in meiosis II gives each gamete one haploid (1n) set. The alleles and maternal-paternal chromosome combination can differ among gametes even though each normal gamete has the same number of chromosome types.

Nondisjunction is failed chromosome separation. It produces gametes with an abnormal chromosome number, so it is not simply another normal outcome of independent assortment. Details of plant and animal sexual life cycles are outside the required AP scope.