meiosis
TRANSCRIPT
Cell DivisionCell Division
Mitosis Meiosis
The stages of mitotic cell division in an animal cell:G2 phase; prophase; prometaphase
.The stages of mitotic cell division in an animal cell:metaphase; anaphase; telophase and cytokinesis
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1. mother cell give 2 daughter cells2. Each daughter cell have :
: The same number of chromosome equal to mother cell: Set of chromosome equal to mother cell: Genetic material as the same as mother cell
2n = 41 chromosome
has 1 chromatid
Mother cell2n = 4
2 Daughter cell
Mitosis is complete : Two new cells are formed.
1 chromosome has 2 chromatid
1 chromosomehas
1 chromatid
2n = 4
OBJECTIVES
. 1. Describe events associated with meiosis 2. Distinguish the phases of meiosis on permanent slides
Plants : slides Lilium anther and Lilium ovaryAnimal : Grasshopper's testis, Crayfish's testis
and frog's testis4. Stain and examine chromosomes squashes in Chinese
chive's flower
MeiosisMeiosis
Reduction
2n = 4 n = 2(Haploid)( Diploid)
1. Reduction of number chromosome2. Reduction of set chromosome
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KeyHaploid (n)Diploid (2n)
Haploid gametes (n = 23)
Egg (n = 23 )
Sperm (n = 23 )
MEIOSIS FERTILIZATION
Ovary TestisDiploid zygote
(2n = 46)
Multicellular diploid adults (2n = 46)
Location for meiosis division
For Plant; Male : occur in cone or anther Female : occur in cone or ovule
Angiosperm
Female conesMale cones
Gymnosperm
Location for meiosis division
For Animal; Male : occur in testis Female : occur in ovary
FrogMale Female
Location for meiosis division
For Human; Male : occur in testis Female : occur in ovary
HumanMale Female
Meiosis involves two divisions
Meiosis I : is a reductional division: produces two haploid cells
Diploid cell
Haploid cell
Meiosis II : is a mitotis-like: produces two haploid cells
Meiosis (Meiotic cell division)
Meiosis II
Prophase IIMetaphase IIAnaphase IITelophase II
Meiosis I
Prophase IMetaphase IAnaphase ITelophase I
LeptoteneZygotenePachyteneDiploteneDiakinesis
InterphaseInterphase
Similar to those of mitosis Similar to those of mitosis but occur in sex organbut occur in sex organ
Interphase is composed of : G1 (gap phase 1) – time of cell growth: S phase – synthesis of DNA (DNA replication)
2 sister chromatids are produced: G2 (gap phase 2) – growth and preparation for meiosis
1 chromosome has
1 chromatid
2n = 4 2n = 4
S , G2G1
1 chromosome has
2 chromatids
MeiosisMeiosis
: Genetic material dispersed in the nucleus as long strands of chromatin
: Thin chromatin strands commonly appear as amorphous granular material
: Presence of nuclear membrane and nucleolus
InterphaseInterphase
nucleolus
chromatin
nucleus
Prophase I
Differs from prophase of mitosis
Homologous chromosomes come to lie sideby side in a pairing process called synapsis.
Each pair of synapsed chromosomes is called a bivalent(two chromosomes) or a tetrad (four chromatids)
synapsis.
Mitosis Meiosis
due to
The events of prophase I can be subdivided into five stages
1. Leptotene
2. Zygotene
3. Pachytene
4. Diplotene
5. Diakinesis
1.1 Leptotene or Leptonema (slender ribbon)
• Long, thin chromosomes start to condense • Nucleolus presence
Prophase I
Nucleolus
1.2 Zygotene or Zygonema (paring)
bivalenttetrad
: Chromosomes condense : Homologous chromosomes come to lie side by side in a
pairing process called synapsis: Each pair of synapsed chromosomes is called a bivalent
(two chromosomes) or a tetrad (four chromatids)
2n = 41 chromosome
has 2 chromatids
1.3 Pachytene (thick ribbon)
: Chromosomes more condense : Nonsister chromatids of a tetrad crossover, called this phenomena
crossing over resulting in an exchange of genetic materialcalled genetic recombinant
: The point of exchange appears as a cross-shaped figure called a chiasma
Chiasma
1.4 Diplotene or Diplonema (double)
: The paired of homologous chromosomes separate: The chromosomes themselves uncoil a bit : The homologous chromosomes of each bivalent
remain tightly bound at chiasmata
1.5 Diakinesis (moving apart)
: The final stage of the first prophase of meiosis: The chromosomes reach their maximal condensation
at this stage : The nucleoli and nuclear membrane disappear: The spindle fiber reform
2n = 4
1 chromosome has
2 chromatids
Metaphase I
The bivalents orient at random on the equatorial plane
2n = 4
1 chromosome has
2 chromatids
Mitosis : Metaphase Meiosis I : Metaphase I
2n = 41 chromosome has 2 chromatids
Anaphase I
: The homologous pairs of chromosomes separate and move to opposite poles
: The centromeres do not separate, but continue holdsister chromatids together ,so each chromosomes consists of two sister chromatids
: This stage reduces the chromosome number from the diploid (2n) to the haploid (n) state.
haploid, nMetaphase I
4n = 8 2n = 4
Mitosis: Anaphase Meiosis I : Anaphase I
1 Chromosomehas
1 Chromatids
1 Chromosomehas
2 Chromatids
*** Note ***Mitosis
Metaphase
Anaphase
Metaphase I
Anaphase I
Meiosis ITelophase I
: Chromosomes have reached their polar destinations : Nuclear membrane and nucleolus reforms : Cytokinesis occurs
Anaphase I
After finish Telophase I
1. Mother cell give 2 haploid daughter cells2. Each haploid daughter cell have :
: The number of chromosomes reduced by half of mother cell : Each chromosome has two chromatid ( diad chromosome ): Set of chromosome reduced by half of mother cell: Genetic material may be or may not be uniformly
2n = 4
n = 2
1 chromosomehas 2 chromatids
1 chromosomehas 2 chromatids
2n = 4
2n = 42n = 4
2n = 4
n = 2 n = 2
After Meiosis IAfter Mitosis
1 chromosomehas
1 chromatids
1 chromosomehas
2 chromatids ( Diad chromosome )
Short Interkinesis
After finish Telophase IEach haploid daughter cell
Go into Mitosis II
: Chromosomes may uncoil and return to an interphase-like condition with reformation of a nuclear membrane
: No DNA synthesis occurs during interkinesis.
No short Interkinesis
: Immediately go into
Prophase II
Meiosis II : similar to those of Mitosis
Prophase II
: The chromosomes recondense. : Nuclear membrane and nucleolus disappear: Spindle fiber reform: Each chromosome has 2 chromatids ( Diad chromosome)
n = 2
1 chromosomehas
2 chromatids( Diad chromosome )
Metaphase IIProphase II Metaphase II
n = 21 chromosome
has 2 chromatids
( Diad chromosome )
: Chromosome more condense: The individual chromosomes have lined up
on the equatorial plane
Anaphase IIMetaphase II Anaphase II
: The centromeres of each chromosome separate : Spindle fiber separate sister chromatids to be
pulled apart (now, referred to again as chromosomes)
2n = 41 chromosome
has 1 chromatids
( Monad chromosome
Telophase II
: Chromosomes begin to uncoil: Nuclear membrane and nucleolus reappears in
each new nucleus: Spindle fiber degenerate
Anaphase II Telophase IIAfter finish Telophase II
Begin with each haploid daughter cell
Each haploid daughter cell give two haploid progeny cells
n = 21 chromosome
has 2 chromatids
( Diad chromosome )
n = 21 chromosome
has 1 chromatids
( Monad chromosome )
Telophase IITelophase I
n = 21 chromosome
has 2 chromatids
( Diad chromosome )
n = 21 chromosome
has 1 chromatids
( Monad chromosome )
Compare between Telophase I and Telophase II Conclution : Meiosis
: From 1 diploid mother cell gives four haploid progeny cells: The number of chromosomes reduced by half of mother cell: Set of chromosome reduced by half of mother cell: Genetic material may not be uniformly of either maternal
or paternal origin
41
To produce gamete : egg or sperm
involved
Fertilization
Why meiosis division have to reduce set of chromosomeand number of chromosome
To maintain the same species
Why meiosis division have to reduce set of chromosomeand number of chromosome
Haploid sperm
Diploid zygote
Haploid egg
Diploid dad
Diploid mom
Equal to parent
Equal to parent
2n = 6
n = 3
n = 3
2n = 6
2n = 6
To maintain the same species
Why meiosis division have to reduce set of chromosomeand number of chromosome
46
46 46
92?
Genetic variation
After fertilization
46
47
Possibility 1 Possibility 2
Two equally probablearrangements ofchromosomes at
metaphase I
Metaphase II
Daughtercells
Combination 1 Combination 2 Combination 3 Combination 4
The independent assortment of homologous chromosomesin metaphase I
Mom's posssible gametes(2n)
Dad's posssible gametes(2n)
N = Number of chromosome pairs
22 = 4
Result of Independent assortment
22 = 4
Egg
Sperm
MEIOSIS FERTILIZATION
OvaryTestis
Multicellular diploid adults (2n = 46)
223 = 8,388,608
Human posssible gametes from independent assortment
223 = 8,388,608
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Crossing over in prophase I
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Genetic variation
EXTINCTION!!
Globalwarming
Survival
Globalwarming
Genetic diversity lead to selection
No genetic variation
1. Study meiosis in the anther of Chinese chive's flower by Squash technique
6 stamens, a singleslender style
HCl 10 min
1
2
3
4
5
6
7
Bring the anther part of Chinese chive's flower on a clean slide. Add a drop of 5% HCland leave for 5-10 min.to causing cell wallto be softed and easily for squashing
Break up the tissue with a dissecting needle
Add a drop of aceto-orcein stain the tissuefor 3-5 min.
Tease the tissue apart with dissecting needles
Cover with a coverslip
Spread the cells out by gently pressing down on the coverslip with your finger or a pencil eraser
Gently pass the slide over a flame , then use microscope focus on low power, and thenswitch to medium or high power to find
meiosis I and meiosis II
Squash technique
2. Distinguish the phases of meiosis in Lilium antheron permanent slides
Plants Slides Lilium anther
3. Distinguish the phases of meiosis in animal testison permanent slides
Grasshopper testis Frog testis Crayfish testis
Plants : Slides Lilium ovary
4. Distinguish the phases of meiosis in Lilium ovaryon permanent slides Result
Finish meiosis I : Diad microspore
Finish meiosis II : Tetrad microspore
1. Study meiosis in the anther of Chinese chive's flower
After finish Meiosis II produce
4 Microspore
Microspore
Study meiosis in the anther of Chinese chive's flower by Squash technique
2.Study meiosis in the Lilium anther on permanent slide
Grasshopper testis Frog testis Crayfish testis
3. Distinguish the phases of meiosis in animal testis on permanent slides
Several lobes of the grasshopper's testis
Grasshopper's testis Early primary spermatocyte Prophase I, substage Pachytene.
Prophase I, substage Diplotene. Prophase I, substage Diakinesis.
Spermatids
Further elongate Mature sperm
heads
tails
Pachytene Diakinesis
Metaphase II
Anaphase IIMetaphase I
Metaphase II
Metaphase I
Telophase I
Telophase I
Spermatid differentiate into sperm ( spermatozoa ) Frog testis
Seminiferous tubule
A
B
Prophase I
Prophase IISperm ( Spermatozoa )
4. Distinguish the phases of meiosis in Lilium ovaryon permanent slides
Megaspore mother cell (2n)
Lilium sp.
2 ( n )
4 nucleate 2(n) + 2(3n)
2 ( 3n )