Meiosis
• Meiosis – a process in which sperm
and egg cells are created by cutting
the chromosome number in half.
• Meiosis goes thru 2 rounds of
division:
– Meiosis I and Meiosis II
– Diploid cell become 4 haploid
cells
– Produces sperm and egg cells
(gametes)
Meiosis I
• Interphase: Chromosomes (DNA) are replicated
before division
• Prophase I: each replicated chromosome pairs with
its homologous chromosome.
– Tetrad: a pair of
homologous
chromosomes with 4
chromatids.
– Crossing-over :
portions of
chromatids, which
contain genes, are
exchanged
Meiosis I
• Metaphase I: paired homologous
chromosomes line up in the center.
• Anaphase 1: spindle fibers separate
each pair of chromosome, pulling
them to opposite ends of the cell.
• Telophase 1: Nuclear envelope forms
around each cluster of chromosomes.
• Cytokinesis: forms two new cells
– The cells are now haploid
– Each cell has a different set of
genes
Chromosomal Mutations
• Chromosomal mutation: mutation
that changes the number or structure
of chromosomes.
– Deletion: The loss of all or part of a
chromosome
– Duplication: A segment is repeated
– Inversion: part of the chromosome
is reversed from its usual direction.
– Translocation: one chromosome
breaks off and attaches to another
chromosome.
Meiosis II
• After meiosis I, chromosomes do not
replicate.
• Cells go through a second round of
divisions (Meiosis II)
– Prophase II – chromosomes form
– Metaphase II – chromosomes line up
at the center
– Anaphase II – chromatids separate
– Telophase II – nucleus reforms
• Result is 4 haploid daughter cells
• Each cell is genetically different