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Meiosis

  • 2 rounds of division

  • Final gametes are haploid (23+23= 46 chromosomes)

A male gamete is called a sperm cell.

A female gamete is called an egg cell.

Human Life Cycle

Zygote → Embryo → Fetus → Human

Stages of meiosis:

  1. Interphase

  2. Meiosis I

  3. Meiosis II

Prophase

Chromosomes will find each other and exchange DNA.

Meiosis I

  • Chromosomes replicate

  • Same size, shape and gene location

  • Alleles may not be the same.

  • Meiosis II splits the cells into haploids

Prophase I

  • Chromatin condenses into chromosomes.

  • Centrioles move to opposite poles

  • Spindle fibres form.

  • The nuclear membrane breaks down.

  • A tetrad is a pair of duplicated homologous chromosomes (together, they have 4 chromatids).

  • Synopsis: The process of forming a tetrad.

Metaphase I

  • Tetrads line up along the equator randomly

  • This is called random assortment and it allows genetic variation.

  • Spindle fibres attach to the pair of sister chromatids.

Anaphase I

  • Chromosome pairs are separated and pulled to the opposite ends.

  • The sister chromatids do NOT separate (this only happens in mitosis).

Telophase I

  • Nuclear membrane reforms.

  • Spindle fibres retract.

Prophase II

  • The nuclear membrane begins to break down.

  • Spindle fibres begin to form.

  • Centrioles begin to move to poles.

  • NO REPLICATION OF DNA

Metaphase II

  • Chromosome pairs align along the equator of the cell.

  • Spindle fibres attach to centromeres of chromatids.

  • Chromatids are no longer identified because of crossing over.

Anaphase II

  • Spindle fibres pull chromatids apart.

Telophase II

  • Nuclear membrane assembles.

  • Chromosomes decondense

  • Spindle fibres disappear.

Humans have 23 pairs of chromosomes.

  • 22 are autosome pairs

  • 1 pair that is sex-determining

Female: XX

Male: XY

For mitosis, check this link.

https://knowt.io/note/874e8eda-7744-4668-86c6-1eecebf7689c/Mitosis

Meiosis

  • 2 rounds of division

  • Final gametes are haploid (23+23= 46 chromosomes)

A male gamete is called a sperm cell.

A female gamete is called an egg cell.

Human Life Cycle

Zygote → Embryo → Fetus → Human

Stages of meiosis:

  1. Interphase

  2. Meiosis I

  3. Meiosis II

Prophase

Chromosomes will find each other and exchange DNA.

Meiosis I

  • Chromosomes replicate

  • Same size, shape and gene location

  • Alleles may not be the same.

  • Meiosis II splits the cells into haploids

Prophase I

  • Chromatin condenses into chromosomes.

  • Centrioles move to opposite poles

  • Spindle fibres form.

  • The nuclear membrane breaks down.

  • A tetrad is a pair of duplicated homologous chromosomes (together, they have 4 chromatids).

  • Synopsis: The process of forming a tetrad.

Metaphase I

  • Tetrads line up along the equator randomly

  • This is called random assortment and it allows genetic variation.

  • Spindle fibres attach to the pair of sister chromatids.

Anaphase I

  • Chromosome pairs are separated and pulled to the opposite ends.

  • The sister chromatids do NOT separate (this only happens in mitosis).

Telophase I

  • Nuclear membrane reforms.

  • Spindle fibres retract.

Prophase II

  • The nuclear membrane begins to break down.

  • Spindle fibres begin to form.

  • Centrioles begin to move to poles.

  • NO REPLICATION OF DNA

Metaphase II

  • Chromosome pairs align along the equator of the cell.

  • Spindle fibres attach to centromeres of chromatids.

  • Chromatids are no longer identified because of crossing over.

Anaphase II

  • Spindle fibres pull chromatids apart.

Telophase II

  • Nuclear membrane assembles.

  • Chromosomes decondense

  • Spindle fibres disappear.

Humans have 23 pairs of chromosomes.

  • 22 are autosome pairs

  • 1 pair that is sex-determining

Female: XX

Male: XY

For mitosis, check this link.

https://knowt.io/note/874e8eda-7744-4668-86c6-1eecebf7689c/Mitosis

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