Download Meiosis

Meiosis
explains Mendel’s law of segregation
Meiosis
● Creates 4 haploid sex
cells from 1 diploid cell
○ haploid- one set of
chromosomes (N)
○ diploid- two sets of
chromosomes (2N)
● Similar to mitosis, but
there are two rounds of
division
2 Rounds of Division
● DNA is copied before meiosis
● MEIOSIS I
○ Divides homologous
chromosomes
■ homologous chromosomestwo sets of similar genetic
information, one set from
each parent
2 Rounds of Division
● Meiosis I Steps
○ Prophase I- nucleus dissolves,
spindle fibers, centrioles, and
chromosomes form
○ Crossing-over occurshomologous chromosomes
trade segments of DNA,
increases genetic variation
2 Rounds of Division
● Meiosis I Steps
○ Metaphase I- homologous
chromosomes line up on
equator
○ “mom” & “dad” chromosomes
mixed up along equator
■ 8,388,608 possible
chromosome combinations
2 Rounds of Division
● Meiosis I Steps
○ Anaphase I- homologous
chromosomes separate
2 Rounds of Division
● Meiosis I Steps
○ Telophase I- nuclei reform,
chromosomes uncoil,
cytokinesis, 2 new haploid (N)
cells are made
○ Mix of “mom” and “dad”
chromosomes
2 Rounds of Division
● MEIOSIS II
○ Divides sister chromatids
○ DNA is not copied before
● Meiosis II Steps
○ Prophase II- chromatin
condenses into chromosomes,
nucleus disappears
2 Rounds of Division
● Meiosis II Steps
○ Metaphase II- chromosomes
line up on equator
2 Rounds of Division
● Meiosis II Steps
○ Anaphase II- chromosomes
separate
2 Rounds of Division
● Meiosis II Steps
○ Telophase II- 4 haploid
cells are made with a
combination of mom and
dad chromosomes
Gametogenesis
● The process of changing haploid
cells from meiosis into sex cells
● Male
○ all 4 cells shrink and develop a
flagellum (tail) -> sperm
○ sperm mainly supplies DNA to
embryo
Gametogenesis
● Female
○ only one cell in meiosis gets most of
the cell material and becomes an
egg
○ other cells become polar bodies and
are broken down
○ egg gives DNA, organelles, and
cytoplasm to embryo
Comparing Mitosis & Meiosis
● Mitosis
○ starts with a diploid cell, ends with 2 diploid cells
○ cells are identical to each other
○ used for growth and repair
● Meiosis
○ starts with diploid cell, ends with 4 haploid cells
○ cells are different
○ used to create new life