• 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