IB Biology Topic D2.1.9 Meiosis as a Reduction Division Revision Notes (SL/HL)

IB Biology Topic D2.1.9 Meiosis as a Reduction Division Revision Notes (SL/HL) | RevisionDojo

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Meiosis Is a Reduction Division: One Diploid Cell Becomes Four Haploid Cells

Definition

Meiosis

Meiosis is a type of cell division that reduces the chromosome number by half, producing four genetically distinct haploid cells. This process occurs in gamete-producing cells and is essential for sexual reproduction.

A diploid cell contains two full sets of chromosomes, written as 2n.
A haploid cell contains one full set of chromosomes, written as n.
Meiosis halves the chromosome number, taking one diploid nucleus to four haploid nuclei.
It does this through two divisions: meiosis I and meiosis II.
The halving happens in meiosis I, which is why meiosis is called a reduction division.

Analogy

Think of a diploid cell as holding a matched pair of gloves, one left and one right, for every chromosome.
Meiosis I hands out one glove of each pair to each new cell.
That is why the set is halved, not just split.

The Big Picture: Two Divisions Take 2n to n

The cell copies its DNA once before meiosis begins.
Two divisions then follow with no further DNA copying in between.
One copy step plus two divisions is what produces four cells, each with half the starting chromosome number.

Meiosis I: Homologous Chromosomes Separate, Halving the Number

Meiosis I is the reduction step: it separates homologous chromosomes so each new cell gets only one chromosome from each pair.

Homologous chromosomes are pairs carrying the same genes in the same order, one inherited from each parent.
During meiosis I the two members of each pair are pulled to opposite ends of the cell.
Each of the two new cells is now haploid because it holds only one chromosome from every pair.

Common Mistake

Meiosis I separates homologous chromosomes, not sister chromatids.
Sister chromatids stay joined all the way through meiosis I.
They are only separated later, in meiosis II.

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Meiosis Is a Reduction Division: One Diploid Cell Becomes Four Haploid Cells

Definition

Meiosis

A diploid cell contains two full sets of chromosomes, written as 2n.
A haploid cell contains one full set of chromosomes, written as n.
Meiosis halves the chromosome number, taking one diploid nucleus to four haploid nuclei.
It does this through two divisions: meiosis I and meiosis II.
The halving happens in meiosis I, which is why meiosis is called a reduction division.

Analogy

Think of a diploid cell as holding a matched pair of gloves, one left and one right, for every chromosome.
Meiosis I hands out one glove of each pair to each new cell.
That is why the set is halved, not just split.

The Big Picture: Two Divisions Take 2n to n

The cell copies its DNA once before meiosis begins.
Two divisions then follow with no further DNA copying in between.
One copy step plus two divisions is what produces four cells, each with half the starting chromosome number.

Meiosis I: Homologous Chromosomes Separate, Halving the Number

Meiosis I is the reduction step: it separates homologous chromosomes so each new cell gets only one chromosome from each pair.

Homologous chromosomes are pairs carrying the same genes in the same order, one inherited from each parent.
During meiosis I the two members of each pair are pulled to opposite ends of the cell.
Each of the two new cells is now haploid because it holds only one chromosome from every pair.

Common Mistake

Meiosis I separates homologous chromosomes, not sister chromatids.
Sister chromatids stay joined all the way through meiosis I.
They are only separated later, in meiosis II.

Definition

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Duis aute irure dolor in reprehenderit

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Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam quis nostrud exercitation.

Excepteur sint occaecat cupidatat non proident

Tip

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Sed do eiusmod tempor incididunt ut labore et dolore magna aliqua.
Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris.
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A - Unity and Diversity9 subtopics

B - Form and Function10 subtopics

C - Interaction and Interdependence9 subtopics

D - Continuity and Change12 subtopics

IB Biology Topic D2.1.9: Meiosis as a Reduction Division Notes

Meiosis Is a Reduction Division: One Diploid Cell Becomes Four Haploid Cells

The Big Picture: Two Divisions Take 2n to n

Meiosis I: Homologous Chromosomes Separate, Halving the Number

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Duis aute irure dolor in reprehenderit

Excepteur sint occaecat cupidatat non proident

Unlock the rest of this chapter with a free account

Meiosis Is a Reduction Division: One Diploid Cell Becomes Four Haploid Cells

The Big Picture: Two Divisions Take 2n to n

Meiosis I: Homologous Chromosomes Separate, Halving the Number

anim nostrud sit dolore minim proident quis fugiat velit et eiusmod nulla quis nulla mollit dolor sunt culpa aliqua

Duis aute irure dolor in reprehenderit

Excepteur sint occaecat cupidatat non proident

Unlock the rest of this chapter with a free account

A - Unity and Diversity9 subtopics

B - Form and Function10 subtopics

C - Interaction and Interdependence9 subtopics

D - Continuity and Change12 subtopics