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Introduction to Meiosis
 http://www.youtube.com/watch?v=toWK0fIyFlY
Types of Reproduction
Two kinds of reproduction:
1. Asexual – one parent produces a
new organism
2. Sexual – 2 parents form a new
individual
Sexual Reproduction
a. Sex Cells – the parent cells aka
sperm and egg through meiosis
Sex cells have only 23
chromosomes instead of 46 – ½
the usual number!
Sexual Reproduction
2. Sperm – the male sex cells
3. Eggs – the female sex cells
Meiosis
Each sperm and egg have only ½ of the
chromosomes so that when sperm
and egg unite, the offspring will have
a total of 46 chromosomes
sperm (23) + egg (23) = 46
MEIOSIS
 Each sperm and egg has only ______ of the
chromosomes from each HOMOLOGOUS
pair.
 Why??
sperm (23) + egg (23) = 46
MEIOSIS
Meiosis – produces new cells with
half the usual number of
chromosomes
via 2 divisions
MEIOSIS
1.Chromosomes are copied once
and the nucleus divides twice
MEIOSIS
Walter Sutton proposed:
Genes are located on
chromosomes!
Male or Female
1. Females have 23 matched
pairs of chromosomes
Male or Female
2. Males have 22 matched pairs
and 1 unmatched pair of
chromosomes
Male or Female
3. Females have only X
chromosomes
 XX
Male or Female
4. Males have X and Y
chromosomes
 XY
Male or Female
An egg fertilized by an X chromosome
will produce a?
An egg fertilized by a Y chromosome
will produce a?
Sex chromosomes carry genes that
determine whether the offspring is
male or female.
STEPS OF MEIOSIS
Use textbook pages 116-117 to
summarize the 8 steps of meiosis
Meiosis
STEPS OF MEIOSIS
1.
Chromosome makes identical copy of itself and make
the X)(Interphase and Prophase 1)
2.
Similar chromosomes pair up, forming homologous
chromosomes and line up at equator (Metaphase 1)
3.
Chromosomes separate from their homologous
partners and move to opposite ends of cell
(Anaphase 1)
STEPS OF MEIOSIS
4. Nuclear membrane reforms and the cell divides into two
identical cells…the chromosomes DO NOT COPY AGAIN!
(Telephase 1 and Cytokinesis 1)
5. Each cell has 1 member of the each homologous pair
(Prophase 2)
6. Chromosomes line up at the equator (Metaphase 2)
STEPS OF MEIOSIS
7. Chromatids pull apart and move to opposite ends
(Anaphase 2)
8. Four new SEX cells are formed from original cell.
Each has ½ the number of chromosomes as the parent
cell. (Telephase 2 and Cytokinesis 2)
Meiosis Square Dance
 http://www.bing.com/videos/search?q=meiosis+squar
e+dance&go=Submit+Query&qs=bs&form=QBVR#vie
w=detail&mid=39074DC66ADD78BDE23139074DC66
ADD78BDE231
Meiosis versus Mitosis
 http://www.pbs.org/wgbh/nova/miracle/divi_flash.ht
ml
 http://www.cellsalive.com/meiosis.htm
 Review Mitosis… purpose and process
 Review Meiosis… purpose and process
 Compare and Contrast Mitosis and Meiosis