SlideShare une entreprise Scribd logo
1  sur  40
Télécharger pour lire hors ligne
11-4 Meiosis

   P275
Homologous chromosomes
• Pair of chromosomes that
  one comes from the male
  parent and the corresponding   Homologous
  one from the female parent     chromosomes



  Homologous ≠ identical         Alleles

     same genes in same loci
     same length
     same shape
     may not the same alleles
     for one gene
Diploid & Haploid Cells

• two copies of each   • one copy of each
  chromosome             chromosome
• homologous pairs     • no homologous pairs
• body cells           • gametes (sex cells)


                         Sperm




                                     Egg
?
       meiosis   Sperm




                                   Egg


Egg

                                 Zygote

                 fertilisation




      Sperm
The purpose of meiosis
is to produce gametes.
A (haploid) gamete
(sex cell, sperm or egg
cell) has half the
number of
chromosomes compared
to a (diploid) somatic
cell (body cell). A male
and a female gamete
may then fuse to form a
zygote, which will have
the same number of
chromosomes as a
somatic cell.
Human chromosomes
– Diploid cells: 23
  pairs of homologous
  chromosomes
– 1st-22nd pairs:
  autosomes
– 23rd pair: sex
  chromosome
Human chromosomes
1-22 pairs : autosomes,   23 pair : sex chormosome
Karyotype (the type of nucleus)
• The number and appearance of the chromosomes in an
  organism
Karyotyping

• Arrange the chromosomes in pairs
  according to their size and structure
      • Collect cells
      • Culture cells
      • Stop cell division at metaphase
      • Staining chromosome
      • Pair (Length, Shape, Position of
        centromeres, Bands)
      • Diagnosis (number, gender,
        abnormality)
How many chromosoems
                                     8
                            How many pairs of
                            homologous
                            chromosomes ?
                                     4
                            How many pairs of
                            autosomes ?
                                    3
                            How many pairs of
Fruit fly’s somatic cells
                            sex
                            chromosomes ?
                                  1 : x,y
A               B
germ cell




                        C          D


            What is the correct gamete
            produced by the germ cell
Meiosis Overview

• reduction division
• number of chromosomes per cell halved
• separation of homologous chromosomes
• 1 diploid  4 genetically different
  haploid
• DNA copied once, cell divide twice
11_4
Sperms are produced by …       meiosis
Diploid parent
      cell                   The
                        chromosomes in
                        the nucleus are
                            copied




     Four haploid
    daughter cells
Diploid       Eggs are also produced by
parent cell            meiosis




                     Haploid
Phases of meiosis


                    MEIOSIS I                       MEIOSIS II
                    PROPHASE I                      PROPHASE II
   interphase                      no interphase
(DNA replication    METAPHASE I (no DNA replication METAPHASE II
before meiosis I)   ANAPHASE I   before meiosis II) ANAPHASE II
                    TELOPHASE I                     TELOPHASE II
Meiosis I
                                 (reduction division)




Interphase I            Prophase I               Metaphase I                Anaphase I             Telophase I

Cells undergo a round   Each chromosome pairs    Spindle fibers attach to   The fibers pull the
of DNA replication,     with its corresponding   the chromosomes.           homologous chromosomes
forming duplicate       homologous chromosome                               toward the opposite ends
Chromosomes.            to form a tetrad.                                   of the cell.
11_4
Prophase 1


•   Supercoil of
    chromosomes
•   Spindle form
•   Synapsis
    (homologous pair to
    form bivalents)
•   Crossing over
•   Nuclear envelope
    breaks down
Synapsis & Crossing over
            • The key to the process of
              meiosis is the Synapsis in
              Prophase I and the splitting of
              the homologues in Anaphase I.
            • One event that can take place
              during meiosis is crossing
              over.
            • Crossing over is the exchange
              of genetic material between two
              homologous chromosomes
              which have paired up during
              Prophase I.
            • The result of crossing over is
              genetic recombination.
Metaphase 1


1. Spindle network
   complete
2. Bivalents line up on
   equator
3. Centromere
   attached to
   microtubules
Anaphase 1


1. Centromeres do not
   split
2. Microtubules
   contract to separate
   homologous pairs
Telophase 1


1. Chromosomes uncoil
2. Spindle breaks down
3. Nuclear envelope
   reform
Meiosis II
                                     (similar to mitosis)



There is no
   DNA
replication




       Prophase II                   Metaphase II              Anaphase II                  Telophase II
       Meiosis I results in two      The chromosomes line up   The sister chromatids        Meiosis II results in four
       haploid (N) daughter cells,   in a similar way to the   separate and move toward     haploid (N) daughter cells.
       each with half the number     metaphase stage of        opposite ends of the cell.
       of chromosomes as the         mitosis.
       original.
Prophase 2


1. Supercoil of
   chromosomes
2. Spindle form
3. Nuclear envelope
   breaks down
Metaphase 2


1. Chromosomes move
   to equator
2. Spindle network
   complete
3. Centromere attach
   to spindle
Anaphase 2


1. Centromere split
2. Microtubules
   contract and sister
   chromatids separate
Telophase 2

1. Chromosomes
   uncoil
2. Spindle breaks down
3. Nuclear envelope
   reforms
Cytokinesis 2

1. 4 haploid cells
2. 1 or many undergo
   differentiation into
   gametes
Which steps in meiosis are
 important in producing
    genetic variety?
1. Crossing over in prophase 1
• Homologous chromosomes exchange nonsister
  chromatids




                   chiasmata
2. Independent assortment in
        metaphase 1

• Bivalents line up on equator in a random way
Possibilities of Crossing over
e.g. 46 chromosomes, 23 pairs
2n = 46; n = 23
2n = 223 = ~ 8 million possible combinations!
3. Random fertilization
Gamete formation in animals

• Male gametes (sperms) are formed through
  spermatogenesis
• Female gametes (egg) are formed through oogenesis
a) Spermatogenesis
spermato-     primary        secondary   spermatids
gonium      spermatocyte   spermatocytes              sperm (n)
                                             (n)
(2n )           (2n)            (n)




Growth        Meiosis I            Meiosis II
b) Oogenesis

                            polar body             polar
                                (n)              bodies (n)




oogonium   primary oocyte
  (2n)          (2n)        secondary
                            oocyte (n)
                                                ovum (n)

 Growth       Meiosis I            Meiosis II
Comparing mitosis and meiosis

• Mitosis: 2 genetically identical diploid cells
• Meiosis: 4 genetically different haploid cells
11_4

Contenu connexe

Tendances (20)

Meiosis 2
Meiosis 2Meiosis 2
Meiosis 2
 
Biology notes-meiosis
Biology notes-meiosisBiology notes-meiosis
Biology notes-meiosis
 
6a: Meiosis
6a: Meiosis6a: Meiosis
6a: Meiosis
 
Meiosis
MeiosisMeiosis
Meiosis
 
meiosis powerpoint presentation
meiosis powerpoint  presentation meiosis powerpoint  presentation
meiosis powerpoint presentation
 
Meiosis Notes
Meiosis NotesMeiosis Notes
Meiosis Notes
 
Meiosis
MeiosisMeiosis
Meiosis
 
Meiosis gamete production with turning point
Meiosis gamete production with turning pointMeiosis gamete production with turning point
Meiosis gamete production with turning point
 
meiosis powerpoint presentation
meiosis powerpoint presentationmeiosis powerpoint presentation
meiosis powerpoint presentation
 
Meiosis
MeiosisMeiosis
Meiosis
 
Meiosis
MeiosisMeiosis
Meiosis
 
Meiosis
MeiosisMeiosis
Meiosis
 
Meiosis 1
Meiosis 1Meiosis 1
Meiosis 1
 
Meiosis
MeiosisMeiosis
Meiosis
 
Meiosis (w/ Mitosis review)
Meiosis (w/ Mitosis review)Meiosis (w/ Mitosis review)
Meiosis (w/ Mitosis review)
 
Meiosis
MeiosisMeiosis
Meiosis
 
Meiosis
MeiosisMeiosis
Meiosis
 
Meiosis
MeiosisMeiosis
Meiosis
 
Bft1033 2 meiosis_print
Bft1033 2 meiosis_printBft1033 2 meiosis_print
Bft1033 2 meiosis_print
 
Meiosis ppt
Meiosis pptMeiosis ppt
Meiosis ppt
 

En vedette

En vedette (20)

Sop presentatie
Sop presentatieSop presentatie
Sop presentatie
 
Resepi kek coklat moist
Resepi kek coklat moistResepi kek coklat moist
Resepi kek coklat moist
 
Illustrations
IllustrationsIllustrations
Illustrations
 
Motivasi for students
Motivasi for studentsMotivasi for students
Motivasi for students
 
Port of Halifax presentation
Port of Halifax presentation Port of Halifax presentation
Port of Halifax presentation
 
Farsi in quattro n 12 novembre 2011
Farsi in quattro n 12 novembre 2011Farsi in quattro n 12 novembre 2011
Farsi in quattro n 12 novembre 2011
 
The wind
The windThe wind
The wind
 
Univers
UniversUnivers
Univers
 
Guia practica para la elaboracion de bibliografias estilo vancouver
Guia practica para la elaboracion de bibliografias   estilo vancouverGuia practica para la elaboracion de bibliografias   estilo vancouver
Guia practica para la elaboracion de bibliografias estilo vancouver
 
Preach preaching semminar
Preach  preaching semminarPreach  preaching semminar
Preach preaching semminar
 
Shallwego
ShallwegoShallwego
Shallwego
 
Bản tin Hoa Sen
Bản tin Hoa Sen Bản tin Hoa Sen
Bản tin Hoa Sen
 
Evaluation question 2
Evaluation question 2Evaluation question 2
Evaluation question 2
 
Menu SPA
Menu SPAMenu SPA
Menu SPA
 
Safety Meeting Starter (SMS) Aug 2012
Safety Meeting Starter (SMS) Aug 2012Safety Meeting Starter (SMS) Aug 2012
Safety Meeting Starter (SMS) Aug 2012
 
Office location photos
Office location photosOffice location photos
Office location photos
 
Print Failover Solutions
Print Failover SolutionsPrint Failover Solutions
Print Failover Solutions
 
niranjan
niranjanniranjan
niranjan
 
συναισθηματικη νοημοσυνη
συναισθηματικη νοημοσυνησυναισθηματικη νοημοσυνη
συναισθηματικη νοημοσυνη
 
Shared Services, Headhunting, Outplacement
Shared Services, Headhunting, OutplacementShared Services, Headhunting, Outplacement
Shared Services, Headhunting, Outplacement
 

Similaire à 11_4 (20)

Lecture 6 Cell Division [Meiosis]
Lecture 6 Cell Division   [Meiosis]Lecture 6 Cell Division   [Meiosis]
Lecture 6 Cell Division [Meiosis]
 
form 4 biology chap5 pt2
form 4 biology chap5 pt2form 4 biology chap5 pt2
form 4 biology chap5 pt2
 
Cell division 2014
Cell division 2014Cell division 2014
Cell division 2014
 
Meiosis
MeiosisMeiosis
Meiosis
 
5.2
5.25.2
5.2
 
Meiosis 1 and 2
Meiosis 1 and 2Meiosis 1 and 2
Meiosis 1 and 2
 
Meiosis
MeiosisMeiosis
Meiosis
 
Meiosis
MeiosisMeiosis
Meiosis
 
meiosis
meiosismeiosis
meiosis
 
Meiosis
MeiosisMeiosis
Meiosis
 
Meiosis Notes
Meiosis NotesMeiosis Notes
Meiosis Notes
 
M.P mabaso
M.P mabasoM.P mabaso
M.P mabaso
 
Meiosis
MeiosisMeiosis
Meiosis
 
Life sciences presentation TST 3B
Life sciences presentation TST 3BLife sciences presentation TST 3B
Life sciences presentation TST 3B
 
Chapter 13: Meiosis
Chapter 13: MeiosisChapter 13: Meiosis
Chapter 13: Meiosis
 
Meiosis
MeiosisMeiosis
Meiosis
 
Proliferasi sel
Proliferasi selProliferasi sel
Proliferasi sel
 
B19 meiosis ppt vocab chapter 10
 B19 meiosis ppt vocab  chapter 10 B19 meiosis ppt vocab  chapter 10
B19 meiosis ppt vocab chapter 10
 
MEIOSIS
MEIOSISMEIOSIS
MEIOSIS
 
meiosis I and II reviewer-Grade 11 .ppt
meiosis I and II reviewer-Grade 11  .pptmeiosis I and II reviewer-Grade 11  .ppt
meiosis I and II reviewer-Grade 11 .ppt
 

Plus de arislantern

Plus de arislantern (10)

13 4 applications of genetic engineering
13 4 applications of genetic engineering13 4 applications of genetic engineering
13 4 applications of genetic engineering
 
13-3 cell transformation
13-3 cell transformation13-3 cell transformation
13-3 cell transformation
 
13-2 manipulating DNA
13-2 manipulating DNA13-2 manipulating DNA
13-2 manipulating DNA
 
12-4
12-412-4
12-4
 
12-3
12-312-3
12-3
 
12-2
12-212-2
12-2
 
12 1
12 112 1
12 1
 
11 3
11 311 3
11 3
 
11 1 2012-h
11 1 2012-h11 1 2012-h
11 1 2012-h
 
11 5 linkage
11 5 linkage11 5 linkage
11 5 linkage
 

Dernier

How to Send Emails From Odoo 17 Using Code
How to Send Emails From Odoo 17 Using CodeHow to Send Emails From Odoo 17 Using Code
How to Send Emails From Odoo 17 Using CodeCeline George
 
Department of Health Compounder Question ‍Solution 2022.pdf
Department of Health Compounder Question ‍Solution 2022.pdfDepartment of Health Compounder Question ‍Solution 2022.pdf
Department of Health Compounder Question ‍Solution 2022.pdfMohonDas
 
Unveiling the Intricacies of Leishmania donovani: Structure, Life Cycle, Path...
Unveiling the Intricacies of Leishmania donovani: Structure, Life Cycle, Path...Unveiling the Intricacies of Leishmania donovani: Structure, Life Cycle, Path...
Unveiling the Intricacies of Leishmania donovani: Structure, Life Cycle, Path...Dr. Asif Anas
 
AUDIENCE THEORY -- FANDOM -- JENKINS.pptx
AUDIENCE THEORY -- FANDOM -- JENKINS.pptxAUDIENCE THEORY -- FANDOM -- JENKINS.pptx
AUDIENCE THEORY -- FANDOM -- JENKINS.pptxiammrhaywood
 
The Stolen Bacillus by Herbert George Wells
The Stolen Bacillus by Herbert George WellsThe Stolen Bacillus by Herbert George Wells
The Stolen Bacillus by Herbert George WellsEugene Lysak
 
Optical Fibre and It's Applications.pptx
Optical Fibre and It's Applications.pptxOptical Fibre and It's Applications.pptx
Optical Fibre and It's Applications.pptxPurva Nikam
 
KARNAADA.pptx made by - saransh dwivedi ( SD ) - SHALAKYA TANTRA - ENT - 4...
KARNAADA.pptx  made by -  saransh dwivedi ( SD ) -  SHALAKYA TANTRA - ENT - 4...KARNAADA.pptx  made by -  saransh dwivedi ( SD ) -  SHALAKYA TANTRA - ENT - 4...
KARNAADA.pptx made by - saransh dwivedi ( SD ) - SHALAKYA TANTRA - ENT - 4...M56BOOKSTORE PRODUCT/SERVICE
 
How to Solve Singleton Error in the Odoo 17
How to Solve Singleton Error in the  Odoo 17How to Solve Singleton Error in the  Odoo 17
How to Solve Singleton Error in the Odoo 17Celine George
 
Slides CapTechTalks Webinar March 2024 Joshua Sinai.pptx
Slides CapTechTalks Webinar March 2024 Joshua Sinai.pptxSlides CapTechTalks Webinar March 2024 Joshua Sinai.pptx
Slides CapTechTalks Webinar March 2024 Joshua Sinai.pptxCapitolTechU
 
Protein Structure - threading Protein modelling pptx
Protein Structure - threading Protein modelling pptxProtein Structure - threading Protein modelling pptx
Protein Structure - threading Protein modelling pptxvidhisharma994099
 
EBUS5423 Data Analytics and Reporting Bl
EBUS5423 Data Analytics and Reporting BlEBUS5423 Data Analytics and Reporting Bl
EBUS5423 Data Analytics and Reporting BlDr. Bruce A. Johnson
 
Drug Information Services- DIC and Sources.
Drug Information Services- DIC and Sources.Drug Information Services- DIC and Sources.
Drug Information Services- DIC and Sources.raviapr7
 
Clinical Pharmacy Introduction to Clinical Pharmacy, Concept of clinical pptx
Clinical Pharmacy  Introduction to Clinical Pharmacy, Concept of clinical pptxClinical Pharmacy  Introduction to Clinical Pharmacy, Concept of clinical pptx
Clinical Pharmacy Introduction to Clinical Pharmacy, Concept of clinical pptxraviapr7
 
How to Make a Field read-only in Odoo 17
How to Make a Field read-only in Odoo 17How to Make a Field read-only in Odoo 17
How to Make a Field read-only in Odoo 17Celine George
 
What is the Future of QuickBooks DeskTop?
What is the Future of QuickBooks DeskTop?What is the Future of QuickBooks DeskTop?
What is the Future of QuickBooks DeskTop?TechSoup
 
DUST OF SNOW_BY ROBERT FROST_EDITED BY_ TANMOY MISHRA
DUST OF SNOW_BY ROBERT FROST_EDITED BY_ TANMOY MISHRADUST OF SNOW_BY ROBERT FROST_EDITED BY_ TANMOY MISHRA
DUST OF SNOW_BY ROBERT FROST_EDITED BY_ TANMOY MISHRATanmoy Mishra
 
Ultra structure and life cycle of Plasmodium.pptx
Ultra structure and life cycle of Plasmodium.pptxUltra structure and life cycle of Plasmodium.pptx
Ultra structure and life cycle of Plasmodium.pptxDr. Asif Anas
 
Education and training program in the hospital APR.pptx
Education and training program in the hospital APR.pptxEducation and training program in the hospital APR.pptx
Education and training program in the hospital APR.pptxraviapr7
 

Dernier (20)

How to Send Emails From Odoo 17 Using Code
How to Send Emails From Odoo 17 Using CodeHow to Send Emails From Odoo 17 Using Code
How to Send Emails From Odoo 17 Using Code
 
Department of Health Compounder Question ‍Solution 2022.pdf
Department of Health Compounder Question ‍Solution 2022.pdfDepartment of Health Compounder Question ‍Solution 2022.pdf
Department of Health Compounder Question ‍Solution 2022.pdf
 
Unveiling the Intricacies of Leishmania donovani: Structure, Life Cycle, Path...
Unveiling the Intricacies of Leishmania donovani: Structure, Life Cycle, Path...Unveiling the Intricacies of Leishmania donovani: Structure, Life Cycle, Path...
Unveiling the Intricacies of Leishmania donovani: Structure, Life Cycle, Path...
 
AUDIENCE THEORY -- FANDOM -- JENKINS.pptx
AUDIENCE THEORY -- FANDOM -- JENKINS.pptxAUDIENCE THEORY -- FANDOM -- JENKINS.pptx
AUDIENCE THEORY -- FANDOM -- JENKINS.pptx
 
The Stolen Bacillus by Herbert George Wells
The Stolen Bacillus by Herbert George WellsThe Stolen Bacillus by Herbert George Wells
The Stolen Bacillus by Herbert George Wells
 
Optical Fibre and It's Applications.pptx
Optical Fibre and It's Applications.pptxOptical Fibre and It's Applications.pptx
Optical Fibre and It's Applications.pptx
 
KARNAADA.pptx made by - saransh dwivedi ( SD ) - SHALAKYA TANTRA - ENT - 4...
KARNAADA.pptx  made by -  saransh dwivedi ( SD ) -  SHALAKYA TANTRA - ENT - 4...KARNAADA.pptx  made by -  saransh dwivedi ( SD ) -  SHALAKYA TANTRA - ENT - 4...
KARNAADA.pptx made by - saransh dwivedi ( SD ) - SHALAKYA TANTRA - ENT - 4...
 
How to Solve Singleton Error in the Odoo 17
How to Solve Singleton Error in the  Odoo 17How to Solve Singleton Error in the  Odoo 17
How to Solve Singleton Error in the Odoo 17
 
Slides CapTechTalks Webinar March 2024 Joshua Sinai.pptx
Slides CapTechTalks Webinar March 2024 Joshua Sinai.pptxSlides CapTechTalks Webinar March 2024 Joshua Sinai.pptx
Slides CapTechTalks Webinar March 2024 Joshua Sinai.pptx
 
March 2024 Directors Meeting, Division of Student Affairs and Academic Support
March 2024 Directors Meeting, Division of Student Affairs and Academic SupportMarch 2024 Directors Meeting, Division of Student Affairs and Academic Support
March 2024 Directors Meeting, Division of Student Affairs and Academic Support
 
Protein Structure - threading Protein modelling pptx
Protein Structure - threading Protein modelling pptxProtein Structure - threading Protein modelling pptx
Protein Structure - threading Protein modelling pptx
 
EBUS5423 Data Analytics and Reporting Bl
EBUS5423 Data Analytics and Reporting BlEBUS5423 Data Analytics and Reporting Bl
EBUS5423 Data Analytics and Reporting Bl
 
Drug Information Services- DIC and Sources.
Drug Information Services- DIC and Sources.Drug Information Services- DIC and Sources.
Drug Information Services- DIC and Sources.
 
Clinical Pharmacy Introduction to Clinical Pharmacy, Concept of clinical pptx
Clinical Pharmacy  Introduction to Clinical Pharmacy, Concept of clinical pptxClinical Pharmacy  Introduction to Clinical Pharmacy, Concept of clinical pptx
Clinical Pharmacy Introduction to Clinical Pharmacy, Concept of clinical pptx
 
Prelims of Kant get Marx 2.0: a general politics quiz
Prelims of Kant get Marx 2.0: a general politics quizPrelims of Kant get Marx 2.0: a general politics quiz
Prelims of Kant get Marx 2.0: a general politics quiz
 
How to Make a Field read-only in Odoo 17
How to Make a Field read-only in Odoo 17How to Make a Field read-only in Odoo 17
How to Make a Field read-only in Odoo 17
 
What is the Future of QuickBooks DeskTop?
What is the Future of QuickBooks DeskTop?What is the Future of QuickBooks DeskTop?
What is the Future of QuickBooks DeskTop?
 
DUST OF SNOW_BY ROBERT FROST_EDITED BY_ TANMOY MISHRA
DUST OF SNOW_BY ROBERT FROST_EDITED BY_ TANMOY MISHRADUST OF SNOW_BY ROBERT FROST_EDITED BY_ TANMOY MISHRA
DUST OF SNOW_BY ROBERT FROST_EDITED BY_ TANMOY MISHRA
 
Ultra structure and life cycle of Plasmodium.pptx
Ultra structure and life cycle of Plasmodium.pptxUltra structure and life cycle of Plasmodium.pptx
Ultra structure and life cycle of Plasmodium.pptx
 
Education and training program in the hospital APR.pptx
Education and training program in the hospital APR.pptxEducation and training program in the hospital APR.pptx
Education and training program in the hospital APR.pptx
 

11_4

  • 2. Homologous chromosomes • Pair of chromosomes that one comes from the male parent and the corresponding Homologous one from the female parent chromosomes Homologous ≠ identical Alleles same genes in same loci same length same shape may not the same alleles for one gene
  • 3. Diploid & Haploid Cells • two copies of each • one copy of each chromosome chromosome • homologous pairs • no homologous pairs • body cells • gametes (sex cells) Sperm Egg
  • 4. ? meiosis Sperm Egg Egg Zygote fertilisation Sperm
  • 5. The purpose of meiosis is to produce gametes. A (haploid) gamete (sex cell, sperm or egg cell) has half the number of chromosomes compared to a (diploid) somatic cell (body cell). A male and a female gamete may then fuse to form a zygote, which will have the same number of chromosomes as a somatic cell.
  • 6. Human chromosomes – Diploid cells: 23 pairs of homologous chromosomes – 1st-22nd pairs: autosomes – 23rd pair: sex chromosome
  • 8. 1-22 pairs : autosomes, 23 pair : sex chormosome
  • 9. Karyotype (the type of nucleus) • The number and appearance of the chromosomes in an organism
  • 10. Karyotyping • Arrange the chromosomes in pairs according to their size and structure • Collect cells • Culture cells • Stop cell division at metaphase • Staining chromosome • Pair (Length, Shape, Position of centromeres, Bands) • Diagnosis (number, gender, abnormality)
  • 11. How many chromosoems 8 How many pairs of homologous chromosomes ? 4 How many pairs of autosomes ? 3 How many pairs of Fruit fly’s somatic cells sex chromosomes ? 1 : x,y
  • 12. A B germ cell C D What is the correct gamete produced by the germ cell
  • 13. Meiosis Overview • reduction division • number of chromosomes per cell halved • separation of homologous chromosomes • 1 diploid  4 genetically different haploid • DNA copied once, cell divide twice
  • 15. Sperms are produced by … meiosis Diploid parent cell The chromosomes in the nucleus are copied Four haploid daughter cells
  • 16. Diploid Eggs are also produced by parent cell meiosis Haploid
  • 17. Phases of meiosis MEIOSIS I MEIOSIS II PROPHASE I PROPHASE II interphase no interphase (DNA replication METAPHASE I (no DNA replication METAPHASE II before meiosis I) ANAPHASE I before meiosis II) ANAPHASE II TELOPHASE I TELOPHASE II
  • 18. Meiosis I (reduction division) Interphase I Prophase I Metaphase I Anaphase I Telophase I Cells undergo a round Each chromosome pairs Spindle fibers attach to The fibers pull the of DNA replication, with its corresponding the chromosomes. homologous chromosomes forming duplicate homologous chromosome toward the opposite ends Chromosomes. to form a tetrad. of the cell.
  • 20. Prophase 1 • Supercoil of chromosomes • Spindle form • Synapsis (homologous pair to form bivalents) • Crossing over • Nuclear envelope breaks down
  • 21. Synapsis & Crossing over • The key to the process of meiosis is the Synapsis in Prophase I and the splitting of the homologues in Anaphase I. • One event that can take place during meiosis is crossing over. • Crossing over is the exchange of genetic material between two homologous chromosomes which have paired up during Prophase I. • The result of crossing over is genetic recombination.
  • 22. Metaphase 1 1. Spindle network complete 2. Bivalents line up on equator 3. Centromere attached to microtubules
  • 23. Anaphase 1 1. Centromeres do not split 2. Microtubules contract to separate homologous pairs
  • 24. Telophase 1 1. Chromosomes uncoil 2. Spindle breaks down 3. Nuclear envelope reform
  • 25. Meiosis II (similar to mitosis) There is no DNA replication Prophase II Metaphase II Anaphase II Telophase II Meiosis I results in two The chromosomes line up The sister chromatids Meiosis II results in four haploid (N) daughter cells, in a similar way to the separate and move toward haploid (N) daughter cells. each with half the number metaphase stage of opposite ends of the cell. of chromosomes as the mitosis. original.
  • 26. Prophase 2 1. Supercoil of chromosomes 2. Spindle form 3. Nuclear envelope breaks down
  • 27. Metaphase 2 1. Chromosomes move to equator 2. Spindle network complete 3. Centromere attach to spindle
  • 28. Anaphase 2 1. Centromere split 2. Microtubules contract and sister chromatids separate
  • 29. Telophase 2 1. Chromosomes uncoil 2. Spindle breaks down 3. Nuclear envelope reforms Cytokinesis 2 1. 4 haploid cells 2. 1 or many undergo differentiation into gametes
  • 30. Which steps in meiosis are important in producing genetic variety?
  • 31. 1. Crossing over in prophase 1 • Homologous chromosomes exchange nonsister chromatids chiasmata
  • 32. 2. Independent assortment in metaphase 1 • Bivalents line up on equator in a random way
  • 34. e.g. 46 chromosomes, 23 pairs 2n = 46; n = 23 2n = 223 = ~ 8 million possible combinations!
  • 36. Gamete formation in animals • Male gametes (sperms) are formed through spermatogenesis • Female gametes (egg) are formed through oogenesis
  • 37. a) Spermatogenesis spermato- primary secondary spermatids gonium spermatocyte spermatocytes sperm (n) (n) (2n ) (2n) (n) Growth Meiosis I Meiosis II
  • 38. b) Oogenesis polar body polar (n) bodies (n) oogonium primary oocyte (2n) (2n) secondary oocyte (n) ovum (n) Growth Meiosis I Meiosis II
  • 39. Comparing mitosis and meiosis • Mitosis: 2 genetically identical diploid cells • Meiosis: 4 genetically different haploid cells