Transcript Meiosis

FROM MOM
FROM DAD
** Mitosis is asexual reproduction & occurs ONLY in regular
old body cells called SOMATIC CELLS (skin, nails, your
pancreas, etc..) NOT sperm and eggs 
** These cells contain autosomal chromosomes that are nonsex chromosomes
** 22 from Mom autosomal chromosomes from mom
and 22 from dad
Diploid (2n) number of chromosomes  you have 44 or 22 pair of
autosomal chromosomes (2n=44)
**Haploid means 1 (n). You receive a haploid
number of chromosomes from mom and a
haploid number from Dad that makes YOU
diploid!! (
**46 in all; 22 autosomal, an X from mom and an
X or Y from dad
**SO there are half as many
chromosomes in gametes (sperm and
eggs)
Replicates
Same types if genes on each
chromosome, just different
variations from each parent


Required for Sexual Reproduction
Similar to Mitosis but there are two sets of phases
and the end result are haploid cells (gametes)
**Produces gametes in the ovaries
(females) and testes (male)
**Results in 4 NON-IDENTICAL haploid (n) cells
 Either sperm or egg
**Diploid to haploid cells
**Genetic Recombination Occurs
From Dad
From Mom
A Tetrad of Homologous
Chromosomes
They Replicate Prior to Meiosis
to form a tedtrad………
Four Haploid
gametes are
produced!!
Look On Page
264 #1-4
**After interphase (DNA replication phase)
**Meiosis I  Prophase I, Metaphase I,
Anaphase I, telophase I and cytokenisis.
**2 cells
**Meiosis II  Prophase II, Metaphase II,
Anaphase II, Telophase II and cytokinesis
**4 cells, the gametes!!
** A reassortment of chromosomes and genetic
information they carry
**crossing over between non-sister
chromatids during Prophase 1
**independent segregation of homologous
chromosomes
**Pink is from your
mom, blue from
your dad
**Non-sister chromatids
exchange genetic
information
**Nondisjunction  BOTH
chromosomes of a
homologous pair (tetrad) fail to separate and move to the
same pole of the cell.
**Occur in all living organisms, but they are
especially common in plants.
**Few harmful gene mutations are passed on to the next
generation because the zygote usually dies. If it lives,
the offspring may have birth defects.
A B C D E
F G H
A B C E
Deletion
F G H
A B C D E
F G H
A B C B C D E
F G H
Insertion
**When part of a chromatid breaks off and attaches to
its sister chromatid
ABCDE FGH
AD CBE FGH
Inversion
**When part of a chromosome breaks off and reattaches
backwards onto the same chromosome
AB C D E F G H
W X AB C DE F G H
WX Y Z
Y
Z
Translocation
**When part of one chromosome breaks off and is
added to a different chromosome, a translocation
occurs.
**Cut them out and paste
them in the correct order !!!
Mitosis
•Occurs in 1 stage
Meiosis
•Occurs in 2 stages
• It is Asexual Reproduction
• For Sexual Reproduction
• Produces “clones” with no
genetic variability
• Produces genetically variability
due to recombination
• Occurs in body cells
(autosomal) and creates two
diploid cells
• Occurs in sex cells called gametes
or germ cells and four haploid cells
(sperm and egg)
• 2n=46  22 pair of
autosomal chromosomes
and 1 pair sex chromosomes
• n=23  22 autosomal
chromosomes and 1 sex
chromosome
•Forms a tetrad
Meiosis
Mitosis