Quick Review
1. What terms are used to describe cells containing
the normal number of chromosomes? Diploid
2. What terms are used to describe cells containing
half the number of chromosomes? Haploid
3. Mitosis produces ________
diploid cells.
4. Meiosis produces ________
haploid cells.
5. How many pairs of chromosomes do human
23 pairs
body cells have? ___
Chromosome Numbers of Some
Common Organisms
Organism
Body Cell (2n)
Gamete (n)
Human
46
23
Garden Pea
14
7
Fruit Fly
8
4
Tomato
24
12
Dog
78
39
Chimpanzee
48
24
Leopard Frog
26
13
Corn
20
10
Apple
34
17
Indian Fern
1260
630
Meiosis I
During prophase I, the ____________
chromosomes coil up and the spindle
______ fibers
form. Then each pair of homologous chromosomes come together to
form a four-part structure called a _____
tetrad (tetra = what number? __).
4 A
tetrad consists of two homologous chromosomes, each made up of
two sister chromatids.
These 4 chromatids in a ______
tetrad are held very close and tightly
together. In fact, they are so close that the arms of non-sister
chromatids can wind and twist around each other, and exchange
genetic information. This is called ________
____. Crossing over
crossing over
results in new combinations of alleles.
The Phases of MEIOSIS
Before meiosis begins: Interphase
Before meiosis begins, what must happen to the cell’s
They must be copied/ duplicated
DNA/ chromosomes?____________________________
Meiosis occurs in sexual reproduction when 1 diploid
germ cell produces 4 haploid cells that can mature to
gametes (sperm or ova).
become _______
Prophase I
Like prophase of mitosis:
1. The nuclear
______membrane
________ disappears.
2. ________
Centrioles move to the opposite
poles and the spindle
_____ fibers
_____ form
between the centrioles.
3. _________
Chromatin condenses into sister
_________
chromatids
Unlike prophase of mitosis:
1. Pairs of homologous chromosomes
tetrads
form ______
Crossing _____
over may occur.
2. ______
Metaphase I
1. Spindle fibers attach to the
kinetochore or centromere
____________________.
metaphase
2. Tetrads line up at the _________
plate.
Anaphase I
1. Tetrads, which consist of two
homologous
chromosomes
_________
__________, separate.
Telophase I / Cytokinesis I
1.
2.
3.
Nuclear
______envelope
_______ reappears.
______
____ disappears.
Spindle fiber
Cytokinesis the division of the
__________,
cytoplasm and the organelles
begins and ends forming two cells.
Meiosis II
The purpose of meiosis II is to
separate _______
________ of each
sister chromatids
chromosome into separate cells.
Prophase II
membrane disappears.
1. The nuclear
_____ _________
Spindle fibers
2. ______
______ form.
3. Chromatin
________ condenses into sister
chromatids
_________
Metaphase II
1. Sister chromatids attach to
spindle fibers
the ______
____
2. Sister chromatids line up at
metaphase plate.
the _________
Anaphase II
1. Sister chromatids separate
chromosomes
into ___________.
2. Chromosomes move to the
poles
opposite _____.
Telophase II
1. Nuclear
______envelope
_______ reforms.
2. 4 gametes
_______ are formed.