Notes for D2.1.11 Meiosis as a source of variation - IB | RevisionDojo
D2.1.11 Meiosis as a source of variation Notes
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 overTip
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
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Question 1
Recap question
If the average number of crossing-over events per bivalent doubles, which of the following best describes the effect on genetic variation in gametes?
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Note
The process of meiosis is essential for sexual reproduction, as it produces gametes (sperm and egg cells) with half the number of chromosomes found in somatic (body) cells. This reduction in chromosome number is crucial because it ensures that when fertilization occurs, the resulting zygote has the correct diploid number of chromosomes.
In humans, somatic cells have 46 chromosomes (23 pairs), while gametes have 23 chromosomes.
Meiosis consists of two consecutive divisions: Meiosis I and Meiosis II.
The chromosome number is halved during Meiosis I, while Meiosis II resembles a mitotic division.
AnalogyThink of meiosis as a two-part recipe: the first part (Meiosis I) divides the ingredients in half, while the second part (Meiosis II) divides each half into individual portions.
