Transcript MEIOSIS - Oakland-Craig Public School

I.
MEIOSIS INTRO
Look Who’s Talking Video
 Sperm and egg are used to
create life.
 How are sperm and egg
created
MEIOSIS
CHAPTER 10.1
I.
MEIOSIS INTRO
A. Organisms have tens of
thousands of genes
B. Genes are not free floating,
they are lined up on
chromosomes
1. Chromosomes can be
about 1000 genes long!
II. MEIOSIS VOCAB
B. Haploid- When a cell has one
kind of chromosome (n)
1. AKA “gamete,” “sex cell,”
“sperm” or “egg.”
F
L
Q
G
F
MEIOSIS VOCAB
A. Diploid- When a cell has two of
each kind of chromosome (2n).
1. Each chromosome has one
allele (1 from mom, 1 from
dad
2. AKA
“Body Cell”
F
f
L
Q
L
q
G
G
F
f
MEIOSIS VOCAB (CONT.)
C. Homologous ChromosomesThe two chromosomes that
make up each pair in a diploid
cell.
F
f
L
Q
L
q
G
G
F
f
They aren’t always
identical, but they
are similar and have
the same genes
MEIOSIS VOCAB (CONT.)
D. Reduction- “Reducing” the
number of chromosomes by ½
(haploid)
1. Why? So after fertilization
the new organism will have
the normal number of
chromosomes (diploid)
REDUCTION
(Making
eggs or
sperm)
Chromosomes Duplicate
III. PHASES OF MEIOSIS
A. Similar to mitosis (Interphase PMAT- Cytokenesis)
B. Goes through PMAT twice
1.
2.
3.
4.
Prophase I
Metaphase I
Anaphase I
Telophase I
5.
6.
7.
8.
Prophase II
Metaphase II
Anaphase II
Telophase II
III. PHASES OF MEIOSIS
C. Interphase
1. Cell growth & metabolism
2. Chromosomes duplicate
(forms the X)
3. Centrioles duplicate
PHASES OF MEIOSIS (cont.)
D. Prophase I
1. Chromosomes coil
(visible)
2. Nuclear membrane
disappears
3. Spindle fibers form
PHASES OF MEIOSIS (cont.)
D. Prophase I (cont)
3. The duplicated
homologous chromosomes
pair up to form a tetrad
PHASES OF MEIOSIS (cont.)
D. Prophase I (cont.)
4. Crossing Over-When
homologous chromosomes
pair so tightly that they
actually exchange pieces of
chromatids
a. See pg. 267 & 269
PHASES OF MEIOSIS (cont.)
4. Crossing Over (cont.)
b. Causes genetic
variation
c. In humans about 2
crossovers occur in every
pair of homologous
chromosomes
PHASES OF MEIOSIS (cont.)
E. Metaphase I
1. The spindle fibers pull the
chromosomes to the center
2. The homologous
chromosomes stay in
tetrads
PHASES OF MEIOSIS (cont.)
F. Anaphase I
1. The homologous
chromosomes are pulled apart
to opposite sides
2. This ensures that each new
cell will get only 1
chromosome
PHASES OF MEIOSIS (cont.)
G. Telophase I
1. Nuclear membrane
reappears
2. Cytokenis occurs (cell splits)
3. You now have 2 cells (each
with 23 chromosome—in
humans)
PHASES OF MEIOSIS (cont.)
G. Meiosis II begins
1. Prophase II, Metaphase II,
Anaphase II, Telophase II
2. It looks like mitosis (same
# of chromosomes), but
there are more cells doing it!
PHASES OF MEIOSIS (cont.)
H. In the beginning…
1. 1 diploid (2 of each
homologous chromosomes)
parent cell
I. End Result
1. 4 haploid (1/2 the original
chromosome number) sex cells
(gametes)
IV. MITOSIS VS. MEIOSIS
MITOSIS
MEIOSIS
Diploid (2n)
Haploid (n)
Beginning: 1 cell Beginning: 1 cell
End: 2 cells
End: 4 cells
Identical to parent
½ parent chromes.
Dup. Chromos
line up alone
Dup. Chromos
line up in pairs
(tetrads)
V. NONDISJUNCTION
A. Nondisjunction- When
homologous chromosomes fail
to separate.
1. One gamete will have an
extra chromosome (trisomy)
2. One gamete will be missing
a chromosome (monosomy)
V. NONDISJUNCTION (cont)
3. Trisomy example
a. Down syndrome
(extra 21st chromosome)
4. Monosomy example
a. Turner’s syndrome
(missing X chromosome)
V. NONDISJUNCTION (cont)
B. Polyploidy- Organisms with
more than the usual number
of chromosomes (3n, 4n, 6n)
1. Plant breeders purposely
cause polyploidy to improve
their produce
a. Bananas (3n), Wheat (6n)
VI. VARIATION
A. Assortment-The many
different ways chromosomes
line up during metaphase
1. See picture on 270
B. Genetic Recombination-Major
source of gene variation due
to reassortment or crossing
over.
VII. GENE MAPPING
A. Crossing over is used to help
scientists map the genes on
each chromosome
1. The farther apart the two
genes are, the more crossing
over there will be.
VII. GENE MAPPING (cont.)
2. Scientists…
1) Start with one known gene
and one unknown gene
2) Find the % of times
they cross over
3) Compare that % to
other genes on the
same chromosome
3. See pg. 272 (Old Books)