Meiosis Leads To Crossing Over
- During Prophase I, homologous chromosomes pair up to form bivalents.
- Non-sister chromatids (chromatids from different homologous chromosomes) exchange segments of DNA.
- This exchange occurs at points called chiasmata (singular: chiasma).
- Crossing over is random and can occur at multiple points along the chromosome, creating many possible genetic combinations.
- The result: chromosomes that contain a mix of maternal and paternal genetic material.
Crossing over is randomand can occur at multiple points along the chromosome, further increasing the number of possible genetic combinations.
Meiosis Leads To Random Orientation of Bivalents
- During Metaphase I, bivalents align at the cell's equator.Each bivalent's orientation is independent of the others.
- The maternal or paternal chromosome of each pair can face either pole, determining which chromosome enters each gamete.
In humans with 23 chromosome pairs, random orientation alone produces 2²³ (over 8 million) possible combinations.
Combined Effect
- Crossing over creates new combinations of alleles on individual chromosomes.
- Random orientation determines which chromosomes from each pair end up together in a gamete.
- Together, these mechanisms ensure that every gamete produced is genetically unique.
- What is the difference between a bivalent and a chiasma?
- Describe how each mechanism of meiosis contributes to genetic variation.
