Meiosis notes Dec 8-16
December 16, 2014
Meiosis- producing
half of DNA to
pass on to offspring
= Gametes
↳ sperm or egg
Meiosis notes Dec 8-16
December 16, 2014
2 stages
1. Meiosis I
(unique)
Prophase I--> Metaphase I --> Anaphase I --> Telophase I
2. Meiosis II
(exactly like mitosis but with
1/2 the chromosomes)
Prophase II--> Metaphase II --> Anaphase II --> Telophase II
Meiosis notes Dec 8-16
December 16, 2014
Meiosis I
Prophase I -
~ 90% of the
time of meiosis
a. chromosomes condense and coil up
b. nuclear membrane dissolves
c. crossing over occurs between non-sister
homologous chromosomes (synapsis)
- homologous chromosomes.
wrap around each other
and exchange genetic
material.
Meiosis notes Dec 8-16
December 16, 2014
-unique mixture of DNA
from both parents that
you can no longer tell if
chromosome is from
mom or dad
Purpose for crossing over
-increases genetic diversity
beyond independent
assortment of chromosomes
Meiosis notes Dec 8-16
December 16, 2014
Metaphase I
-homologous chromosomes stay paired
up and line up side by side along
metaphase plate
- each centromere has only
ONE Kinetochore (not 2)
-centrioles produced spindle fibers
but only grab one homologous
chromosome
Meiosis notes Dec 8-16
December 16, 2014
3. Anaphase I - Homologous
chromosomes are separated
- sister chromosomes
are still connected at
centromere
4. Telophase I --> chromosomes
at opposite poles
- nuclear mebrane reforms
- chromosomes unwind
Cytokinesis- cell splits into
two new cells
* Not functional
Meiosis notes Dec 8-16
December 16, 2014
Meiosis II- exactly like mitosis but
with 1/2 of the chromosomes.
n=2 here
the cells will
finish with
only n
=haploid
Meiosis notes Dec 8-16
December 16, 2014
5. Prophase II -chromosomes condense
- nuclear membrane dissolves
- centrioles move to opposite poles
n=3 still
* Exactly like prophase of mitosis
Meiosis notes Dec 8-16
December 16, 2014
- chromosomes at opposite poles of cell
-nuclear membrane reformes
-chromosomes uncoil
Cytokinesis- all cells separate and contain
only n which is haploid (not 2n like mitosis)
Meiosis notes Dec 8-16
December 16, 2014
Oogenesis- the formation of the egg
1 cell --> 1 supersized egg and 2 polar bodies
Spermatogenesis- formation of the sperm
1 cell--> 4 sperm