Transcript 7 Meiosis Stages

Meiosis I and II Stages
June 2, 2016
Meiosis I
• PROPHASE I:
Centrioles
start to move
to the poles
Spindle
starts to
form
Nuclear
envelope and
nucleous
disappear
Tetrad Formation
Homologous pairs
connect to each other
Synapsis: where
homologous
chromosomes join
together in a
tetrad
Crossing-over:
Exchange of
genetic info
between nonsister chromatids
Recombination (crossing over)
• Occurs in prophase
of meiosis I
A
A
B
B
C
• Generates diversity
D
E
F
b
C
D
E
F
a
a
b
c
c
d
d
e
f
•Creates chromosomes with new combinations
of alleles for genes A to F.
e
f
Recombination (crossing over)
• Occurs in prophase
of meiosis I
A
a
B
b
C
• Generates diversity
Letters denote genes, Case denotes
alleles (dominant vs recessive
versions of the trait)
D
E
F
C
c
c
D
d
E
F
e
f
•Creates chromosomes with new combinations
of alleles for genes A to F.
d
e
f
Recombination (crossing over)
• Occurs in prophase
of meiosis I
a
A
B
b
C
• Generates diversity
Letters denote genes, Case denotes
alleles (dominant vs. recessive
versions of the trait)
D
E
F
A
a
B
b
C
D
E
F
e
c
c
d
d
e
f
•Creates chromosomes with new
combinations of alleles for genes A to F.
f
• METAPHASE I:
Independent
Assortment:
Homologous
pairs
independently
align along
metaphase
plate
Spindle fibers
attach to
centromere of
each
homologous
pair
• ANAPHASE I:
Homologous
pairs separate
and are drawn to
opposite poles
by spindle fibers
Centromeres
remain intact
• TELOPHASE I:
Nuclear
envelope and
nucleous
reappear
Cleavage
Furrow
Spindle
fibers
disappear
Daughter
cells have
one
chromosome
from each
homologous
pair.
• INTERKINESIS:
Period of time between Meiosis I
and Meiosis II
No replication of DNA occurs
Meiosis II
• PROPHASE II:
Centrioles
start to move
to the poles
Spindle
starts to
form
Nuclear
envelope and
nucleous
disappear
• METAPHASE II:
Replicated
chromosomes
align at the
metaphase plate
Spindle fibers
attach to
centromere of
each sister
chromatid
• ANAPHASE II:
Sister
chromatids
separate and
are drawn to
opposite poles
by spindle fibers
Centromeres are
broken
• TELOPHASE II:
Nuclear
envelope and
nucleous
reappear
Cleavage
Furrow
Spindle
fibers
disappear
Daughter cells
have one
unduplicated
chromosome
from each
sister
chromatid.
Have haploid
number (“n”) of
chromosomes
• CYTOKINESIS:
Division of
cytoplasm
Separation of 4
haploid daughter
cells
Remember that
TWO cells were
made from
Meiosis I and
both entered
Meiosis II to get
all 4 cells