Meiosis & Genetic Variation – AP Biology

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Meiosis & Genetic Variation

AP Biology · Unit 4: Cell Communication & Cell Cycle

Learning Objectives

Describe the stages of Meiosis I and II

Explain how crossing over increases genetic diversity

Distinguish between Meiosis I (reductional) and Meiosis II (equational)

Compare Meiosis vs Mitosis outcomes

Explain independent assortment and its genetic impact

Chromosome Color Code

Paternal chromosome (blue)

Maternal chromosome (pink)

Recombinant segment (violet)

Spindle fibers

Key Concepts

Meiosis I: Homologous pairs separate → 2n → n (reductional division).

Meiosis II: Sister chromatids separate → n → n (equational, like mitosis).

Crossing over in Prophase I creates recombinant chromosomes, vastly increasing genetic diversity.

Genetic Variation Sources

Crossing over (recombination)

Independent assortment (2ⁿ combos)

Random fertilization

Meiosis AP Biology Unit 4 Genetics

Interphase (G₂)

2n = 4 (diploid) · DNA replicated

Before meiosis begins, DNA has been replicated. Each chromosome consists of two sister chromatids joined at the centromere. The cell is diploid (2n).

Ploidy2n

Chromosomes4

Chromatids8

Cells1

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Meiosis vs Mitosis

	Meiosis	Mitosis
Divisions	2	1
Daughter cells	4 (haploid)	2 (diploid)
Crossing over	Yes	No
Genetic identity	Unique	Identical
Purpose	Gametes	Growth/Repair

Phase Details

Click through phases to see detailed descriptions here.

📝 Quick Quiz▼

1. In which phase does crossing over occur?

Metaphase I Prophase I Anaphase II Telophase I

2. After Meiosis I, the resulting cells are:

2 diploid cells 2 haploid cells 4 haploid cells 4 diploid cells

3. Which event does NOT contribute to genetic variation in meiosis?

Crossing over Independent assortment DNA replication Random fertilization