1. mother cell give 2 daughter cells 2. Each daughter cell have : : The same number of chromosome equal to mother cell : Set of chromosome equal to mother cell 5 : Genetic material as the same as mother cell
Meiosis
OBJECTIVES
Reduction
. 1. Describe events associated with meiosis 2. Distinguish the phases of meiosis on permanent slides Plants : slides Lilium anther and Lilium ovary Animal : Grasshopper's testis, Crayfish's testis
1. Reduction of number chromosome 2. Reduction of set chromosome
and frog's testis 4. Stain and examine chromosomes squashes in Chinese chive's flower 2n = 4
n=2
( Diploid)
(Haploid)
Haploid gametes (n = 23)
Key Haploid (n) Diploid (2n)
Location for meiosis division
Egg (n = 23 )
For Plant; Male : occur in cone or anther Female : occur in cone or ovule Sperm (n = 23 ) MEIOSIS
Ovary
FERTILIZATION
Gymnosperm
Angiosperm
Testis Diploid zygote (2n = 46)
Multicellular diploid adults (2n = 46)
Male
9
Male cones
Female cones
Location for meiosis division
Location for meiosis division
For Animal; Male : occur in testis Female : occur in ovary
For Human; Male : occur in testis Female : occur in ovary
Frog
Human Female
Male
Female
Meiosis involves two divisions
Meiosis I : is a reductional division : produces two haploid cells
Meiosis II : is a mitotis-like : produces two haploid cells
Meiosis (Meiotic cell division)
Meiosis I
Meiosis II Diploid cell
Prophase I Metaphase I Anaphase I Telophase I
Leptotene Zygotene Pachytene Diplotene Diakinesis
Prophase II Metaphase II Anaphase II Telophase II
Haploid cell
Interphase
G1
Meiosis
S , G2
Similar to those of mitosis but 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
2n = 4 1 chromosome has 1 chromatid
2n = 4 1 chromosome has 2 chromatids
Interphase nucleus
Prophase I
Mitosis
Meiosis
Differs from prophase of mitosis due to
Homologous chromosomes come to lie side by side in a pairing process called synapsis. nucleolus
synapsis.
Each pair of synapsed chromosomes is called a bivalent (two chromosomes) or a tetrad (four chromatids) chromatin : 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
The events of prophase I can be subdivided into five stages
Prophase I 1.1 Leptotene or Leptonema (slender ribbon)
1. Leptotene 2. Zygotene 3. Pachytene
Nucleolus
4. Diplotene 5. Diakinesis
• Long, thin chromosomes start to condense • Nucleolus presence
1.2 Zygotene or Zygonema (paring) 2n = 4
bivalent tetrad
1.3 Pachytene (thick ribbon) Chiasma
1 chromosome has 2 chromatids
: 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)
1.4 Diplotene or Diplonema (double)
: Chromosomes more condense : Nonsister chromatids of a tetrad crossover, called this phenomena crossing over resulting in an exchange of genetic material called genetic recombinant : The point of exchange appears as a cross-shaped figure called a chiasma
1.5 Diakinesis (moving apart)
2n = 4 1 chromosome has 2 chromatids
: The paired of homologous chromosomes separate : The chromosomes themselves uncoil a bit : The homologous chromosomes of each bivalent remain tightly bound at chiasmata
: 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
Metaphase I
Mitosis : Metaphase
Meiosis I : Metaphase I
2n = 4 1 chromosome has 2 chromatids
The bivalents orient at random on the equatorial plane
Metaphase I
Anaphase I
2n = 4 1 chromosome has 2 chromatids
Mitosis: Anaphase
Meiosis I : Anaphase I
haploid, n
: The homologous pairs of chromosomes separate and move to opposite poles : The centromeres do not separate, but continue hold sister 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.
4n = 8
2n = 4
1 Chromosome has 1 Chromatids
1 Chromosome has 2 Chromatids
Mitosis
*** Note ***
Metaphase
Anaphase
Meiosis I
Anaphase I
Telophase I
Metaphase I
Anaphase I
After finish Telophase I
: Chromosomes have reached their polar destinations : Nuclear membrane and nucleolus reforms : Cytokinesis occurs
After Mitosis
After Meiosis I
2n = 4 1 chromosome has 2 chromatids
2n = 4
2n = 4
n=2 1 chromosome has 2 chromatids
1. Mother cell
give 2 haploid daughter cells 2. 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 1 chromosome has 1 chromatids
2n = 4
n=2
n=2
1 chromosome has 2 chromatids ( Diad chromosome )
Meiosis II : similar to those of Mitosis
After finish Telophase I Each haploid daughter cell
Prophase II n=2
Go into Mitosis II
Short Interkinesis
1 chromosome has 2 chromatids ( Diad chromosome )
No short Interkinesis
: Chromosomes may uncoil and return to an interphase-like condition with reformation of a nuclear membrane : No DNA synthesis occurs during interkinesis.
: Immediately go into Prophase II
: The chromosomes recondense. : Nuclear membrane and nucleolus disappear : Spindle fiber reform : Each chromosome has 2 chromatids ( Diad chromosome)
Metaphase II Prophase II
Anaphase II Metaphase II
Metaphase II
n=2 1 chromosome has 2 chromatids ( Diad chromosome )
: Chromosome more condense : The individual chromosomes have lined up on the equatorial plane
: The centromeres of each chromosome separate : Spindle fiber separate sister chromatids to be pulled apart (now, referred to again as chromosomes)
Telophase II Anaphase II
Telophase II
After finish Telophase II Begin with each haploid daughter cell n=2 1 chromosome has 2 chromatids ( Diad chromosome )
n=2 : Chromosomes begin to uncoil : Nuclear membrane and nucleolus reappears in each new nucleus : Spindle fiber degenerate
Compare between Telophase I and Telophase II Telophase I
Telophase II
n=2
n=2
1 chromosome has 2 chromatids ( Diad chromosome )
1 chromosome has 1 chromatids ( Monad chromosome )
1 chromosome has 1 chromatids ( Monad chromosome )
Each haploid daughter cell give two haploid progeny cells
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
Why meiosis division have to reduce set of chromosome and number of chromosome involved
To produce gamete : egg or sperm
Fertilization
41
Why meiosis division have to reduce set of chromosome and number of chromosome
Why meiosis division have to reduce set of chromosome and number of chromosome
To maintain the same species
To maintain the same species
Equal to parent
46
Haploid sperm
n=3
Diploid dad
2n = 6
? 46 Diploid zygote
2n = 6 Haploid egg
Diploid mom
2n = 6
46
n=3 Equal to parent
92
After fertilization
Genetic variation
46
The independent assortment of homologous chromosomes in metaphase I
Result of Independent assortment
Possibility 2
Possibility 1 Two equally probable arrangements of chromosomes at metaphase I
Dad's posssible gametes
Metaphase II
(2n)
Daughter cells
22 = 4
Mom's posssible gametes
(2n) 22 = 4
47
Combination 1 Combination 2
Combination 3 Combination 4
N = Number of chromosome pairs
Human posssible gametes from independent assortment Egg Sperm MEIOSIS
223 = 8,388,608 223 = 8,388,608
FERTILIZATION
Testis Ovary
Multicellular diploid adults (2n = 46)
50
Crossing over in prophase I
52
Genetic diversity lead to selection
Global warming
Survival
Genetic variation
Global warming
EXTINCTION!!
No genetic variation
1. Study meiosis in the anther of Chinese chive's flower by Squash technique
Squash technique 1 HCl 10 min
Bring the anther part of Chinese chive's flower on a clean slide. Add a drop of 5% HCl and leave for 5-10 min.to causing cell wall to be softed and easily for squashing
4 Tease the tissue apart with dissecting needles
5 Cover with a coverslip
2 6 Break up the tissue with a dissecting needle
3
Spread the cells out by gently pressing down on the coverslip with your finger or a pencil eraser
7
6 stamens, a single slender style Add a drop of aceto-orcein stain the tissue for 3-5 min.
Gently pass the slide over a flame , then use microscope focus on low power, and then switch to medium or high power to find meiosis I and meiosis II
2. Distinguish the phases of meiosis in Lilium anther on permanent slides
3. Distinguish the phases of meiosis in animal testis on permanent slides Grasshopper testis
Frog testis
Crayfish testis
Plants Slides Lilium anther
4. Distinguish the phases of meiosis in Lilium ovary on permanent slides
Plants : Slides Lilium ovary
Result
1. Study meiosis in the anther of Chinese chive's flower
Finish meiosis I : Diad microspore
Study meiosis in the anther of Chinese chive's flower by Squash technique
After finish Meiosis II produce 4 Microspore
Microspore
Finish meiosis II : Tetrad microspore
2.Study meiosis in the Lilium anther on permanent slide
3. Distinguish the phases of meiosis in animal testis on permanent slides
Grasshopper testis
Grasshopper's testis
Frog testis
Early primary spermatocyte
Crayfish testis
Prophase I, substage Pachytene.
Several lobes of the grasshopper's testis
Prophase I, substage Diplotene.
Prophase I, substage Diakinesis.
Spermatids
Pachytene
heads tails
Further elongate
Mature sperm
Metaphase II Metaphase II Anaphase II Metaphase I Telophase I Telophase I Metaphase I
Diakinesis
Spermatid differentiate into sperm ( spermatozoa )
Frog testis
Seminiferous tubule
Sperm ( Spermatozoa )
B
Prophase II
A Prophase I
4. Distinguish the phases of meiosis in Lilium ovary on permanent slides
