Do Now
Take out 10.2 vocabulary homework
 Complete handout

– Remember
 haploid = half
 Diploid = double
– So if 20 is the diploid number, then
10 is the haploid number.
- If 5 is the haploid number, then
10 is the diploid number
HOMEWORK: STUDY FOR YOUR MIDTERM!
Meiosis:
Making haploid reproductive cells
Goal of Meiosis
The purpose is to make haploid cells so that when 2
haploid cells combine you have a new diploid
offspring that has an original combination of genes.
+
Haploid cell
(1n)
+ Haploid cell
(1n)
=
= Diploid cell (2n)
that turns into a
muticellular offspring
Meiosis Overview
o
o
o
Makes 4 haploid cells
Takes place in sex cells (gametes) such as egg
& sperm cells
Location: Testes (male) and ovaries (female)
o The
Goal:
o To make 4 haploid daughter cells for reproduction
that are genetically different from the parent cells.
o Each haploid daughter cell will contain a mixture of
the parents chromosomes, so that the 4 daughter
cells should be different.
Meiosis
 Involves
2 cell divisions
 The
cell will go through interphase
(G1, S, G2)…but then will divide
twice  resulting in 4 haploid cells
 There
are 2 parts in Meiosis:
– Meiosis 1
– Meiosis 2
Meiosis I and Meiosis II

Both go through each of the
phases of mitosis (PMAT)

After each one cytokinesis
occurs

The goal is to reduce
chromosome number to
haploid so that 2 cells can
combine to make a diploid
organism
Meiosis 1: Prophase 1





DNA coils into
chromatids
Spindle fibers appear
Nucleus/nucleolus
disappear
*Homologous
chromosomes pair up
into tetrads of 4
chromatids, called
synapsis
*Crossing over may
occur causing genetic
recombination
What is crossing over?
 When
a homologous pair bumps into each
other during prophase I and they exchange
portions one chromatid  leads to genetic
recombination
Metaphase I

Metaphase I:
& Anaphase I

Anaphase I:
Tetrads line up
Homologous pairs split
randomly in the
randomly
center. Spindle fibers
attach to each end of
the homologous pair
Independent Assortment
The random lining up of homologous pairs during
metaphase I. This allows for different gametes to be
possible and also leads toward genetic recombination
More independent assortment
What is genetic recombination?

…when the combination of genes in an offspring
are different from the gene combination found in
the parents

Occurs in 2 ways in meiosis
1. Crossing over where homologous pairs exchange
portions of one chromatid
2. Independent assortment where the homologous pairs
line up randomly or without influences like which
parent they came from or whether they are dominant
or recessive.
Telophase I and Cytokinesis I
Chromosomes reach poles
 Cytokinesis occurs forming
2 new cells.
 Nuclear membrane may or
may not reform before
meiosis II

Meiosis II
(2nd cell division, similar to mitosis steps, PMAT)





Prophase II: Spindle fibers form
Metaphase II: Chromosomes move to center (along equator)
Anaphase II: Chromatids separate toward the poles
Telophase II: Nuclear membrane reforms. Spindle fibers disassemble.
Cytokinesis occurs forming 4 haploid cells with 1 copy of each
chromosome.
Do Now –
complete on a blank piece of paper with
the date and place in your do now section

1. Where does Meiosis take place in the
body?
– Sex cells

2. What kind of cells does Meiosis
produce?
– Haploid

3. What are the two ways that Meiosis
causes genetic recombination?
– Crossing over and independent assortment

Homework: Meiosis handout
How does Meiosis differ in males vs. females?
Since meiosis is producing sex cells (sperm & eggs) it takes place
in the testes (males) & the ovaries (female)

In males:
– Spermatogenesis - the formation of 4
spermatids (haploid cells) which will turn into
spermatozoa (sperm cells).

In females:
– Oogenesis - the formation of 1 egg cell (ova) with
more cytoplasm than the other 3 cells. The
remaining 3 cells are called polar bodies and will
disintegrate
The
phases
of
Meiosis
Diagrams
Let us compare
Mitosis VS. Meiosis
Mitosis makes
IDENTICAL cells to the
parent
 Mitosis make DIPLOID
cells
 Mitosis occurs in BODY
cells
 Mitosis makes 2
DAUGHTER CELLS

Meiosis make
DIFFERENT cells from
the parent
 Meiosis makes HAPLOID
cells
 Meiosis occurs in
REPRODUCTIVE cells
 Meiosis makes 4
DAUGHTER CELLS

Meiosis square dance
Take a set of lyrics AND
 Get ready to sing 


Meiosis square dance
Animations
Johnkyrk.com
http://www.lewport.wnyric.org/jwanamaker/
animations/meiosis.html
http://www.stolaf.edu/people/giannini/

Meiosis square dance