Meiosis Notes

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Transcript Meiosis Notes

Chapter 10 Section 2 NotesMeiosis
• Gene--A segment of DNA that controls
production of a protein, exists on a chromosome
• A chromosome--can contain a thousand or
more genes along its length
Chromosome
• In most animals and plants--chromosomes
occur in pairs
• Humans--have 23 pairs or 46 total
chromosomes
•Homologous chromosomes--The 2 chromosomes of
a pair
• Diploid--A cell in which the chromosomes occur in
pairs (2n)
•Human body cells--are diploid and have a pair of
each chromosome
• Haploid--A cell that contains only one chromosome from
each pair (n)
•Gametes--haploid sex cells.
•male=sperm female=egg
Diploid and haploid cells
Chromosome Numbers of Common Organisms
Organism
Body Cell (2n) Gamete (n)
4
Fruit fly
8
Garden pea
14
7
10
Corn
20
12
Tomato
24
Leopard Frog
26
13
Apple
34
17
Human
46
23
Chimpanzee
24
48
Dog
78
39
Adder’s tongue fern
1260
630
• This table
shows the
diploid and
haploid number
of chromosomes
of some species.
• Fertilization--fusion of male and female gametes to
form zygote
•Zygote--diploid cell (2 of each chromosome)
•Sexual reproduction--production and
combination of gametes
• Meiosis--Cell division that produces gametes that
have 1/2 the number of chromosomes as the parent
cell (haploid)
•Meiosis has--2 separate cell divisions, meiosis I
and meiosis II Haploid
gametes
Sperm Cell
(n=23)
Meiosis
Egg
Cell
Fertilization
Diploid
zygote
(2n=46)
Mitosis and
Development
Multicellular
diploid adults
(2n=46)
• Meiosis begins with 1 diploid cell and ends with 4
haploid cells or gametes
• Each gamete has half the number of
chromosomes as a diploid cell
Meiosis II
1 diploid cell with
4 chromosomes
4 haploid cells with
2 chromosomes each
Meiosis I
•Prophase I
•DNA coils into tetrads
•Spindle forms
•Crossing over--DNA is swapped
between chromosomes in a pair
Meiosis I
•Metaphase I
•Tetrads (2 pairs of homologous chromosomes) line
up along the equator of the cell
Meiosis I
•Anaphase I
•Tetrads are separated into
chromosome pairs and
move to opposite ends of
the cell
Meiosis I
•Telophase I
•Spindle disappears
•Chromosomes uncoil
•Cytoplasm divides into
2 cells
Meiosis II
• Meiosis II--has 4 stages, prophase II, metaphase II,
anaphase II, and telophase II
•Each stage--occurs just like the stages of mitosis
Prophase II
Metaphase II
Anaphase II
Telophase II
Meiosis II
Prophase II:



A spindle forms in each of the 2 new
cells
Spindle fibers attach to the
chromosomes
Nuclear envelope disappear
Metaphase II

The sister chromatids line up
in the middle of the cell at the
equator.
Meiosis II
Anaphase II:


Centromere of the
chromosomes split, allowing the
sister chromatids to separate
The chromatids begin to move
to the opposite ends of the cell
Meiosis II
Telophase II:



Sister chromatids reach
opposite ends of the cell
Spindles disappear and the
nuclear envelope appears
Cytoplasm divides
MEIOSIS
Comparison of Mitosis and Meiosis
Mitosis
Occurs in most body
cells
One division
Meiosis
Occurs only in sex cells
Two divisions
One cell makes 2 diploid One cell makes 4
cells
haploid cells
Identical to the parent
Different from parent
The Phases of Meiosis
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