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Meiosis
Biren Daftary
Background
• Occurs in sex cells or gametes
• After undergoing meiosis, the chromosome
number of a cell is reduced by half...
Meiosis I
• In Meiosis I, a sex cell divides into two cells and
the chromosome number is halved
• It has 4 phases: Prophas...
Prophase I
• Longest and most complex phase (90%).
• Chromatin condenses to form chromosomes.
• Synapsis occurs: homologou...
Tetrad & Crossing over
Homologous
chromosomes after
crossing over
Metaphase I
•It is the shortest phase
•The tetrads align on the
metaphase plate
•Spindle fibers attach to the
kinetochores...
Anaphase I
• Homologous chromosomes
separate and move towards
the poles.
• Sister chromatids remain
attached at their cent...
Telophase I
• Each pole now has haploid
set of chromosomes.
• Cytokinesis occurs and two
haploid daughter cells are
formed...
Meiosis II
• In meiosis II, the chromosome number doesn’t
change when compared to meiosis 1 products
• Hence, Meiosis II i...
Prophase II
• Same as prophase in mitosis
• Chromatin get condensed to
form chromosomes
• The spindle fibers are formed
• ...
Metaphase II
• Same as metaphase in Mitosis
• The chromosomes align
themselves on the metaphase
plate
• The spindle fibers...
Anaphase II
• Same as anaphase in Mitosis
• Homologous chromosomes do
not separate
• Sister chromatids separate
• Each chr...
Telophase II
• Same as telophase in Mitosis
• Nuclei are formed.
• Cytokinesis occurs.
• 4 haploid daughter cells produced...
Meiosis
summary
Fertilization
• The fusion of a sperm(n) and egg(n) to form a zygote.
• A zygote is a fertilized egg (2n)
• 2n=diploid, n=...
Meiosis
Meiosis
Meiosis
Meiosis
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Meiosis

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Meiosis made easy for students. Meiosis is a part of the Biology syllabus prescribed by the Maharashtra Board for 11th standard curriculum

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Meiosis

  1. 1. Meiosis Biren Daftary
  2. 2. Background • Occurs in sex cells or gametes • After undergoing meiosis, the chromosome number of a cell is reduced by half • Meiosis is necessary in the formation of male & female gametes • Hence gametes have half the number of chromosomes as compared to other normal cells • Entire meiosis is composed of two parts: Meiosis I & meiosis II
  3. 3. Meiosis I • In Meiosis I, a sex cell divides into two cells and the chromosome number is halved • It has 4 phases: Prophase I, Metaphase I, Anaphase I & Telophase I • Meiosis I is followed by meiosis II immediately without the cell going into interphase *Interphase is the duration between two successive mitotic/meiotic phases consisting of 3 phases: G1, S & G2
  4. 4. Prophase I • Longest and most complex phase (90%). • Chromatin condenses to form chromosomes. • Synapsis occurs: homologous chromosomes come together to form a tetrad. • Tetrad is two chromosomes or four chromatids (sister and non-sister chromatids). • Crossing over of genes occurs in the tetrad *Homologous chromosomes are a pair of chromosomes, one obtained from each parent. They are similar but not identical
  5. 5. Tetrad & Crossing over Homologous chromosomes after crossing over
  6. 6. Metaphase I •It is the shortest phase •The tetrads align on the metaphase plate •Spindle fibers attach to the kinetochores of the centromeres
  7. 7. Anaphase I • Homologous chromosomes separate and move towards the poles. • Sister chromatids remain attached at their centromeres.
  8. 8. Telophase I • Each pole now has haploid set of chromosomes. • Cytokinesis occurs and two haploid daughter cells are formed. *Cytokinesis is the physical process of cell division in which the nucleus & cytoplasm divide giving rise to 2 cells
  9. 9. Meiosis II • In meiosis II, the chromosome number doesn’t change when compared to meiosis 1 products • Hence, Meiosis II is similar to mitosis • Meiosis II consists of 4 stages: Prophase II, Metaphase II, Anaphase II & Telophase II
  10. 10. Prophase II • Same as prophase in mitosis • Chromatin get condensed to form chromosomes • The spindle fibers are formed • The centrosomes begin to move towards either of the poles
  11. 11. Metaphase II • Same as metaphase in Mitosis • The chromosomes align themselves on the metaphase plate • The spindle fibers attach to the kinetochores on the centromeres
  12. 12. Anaphase II • Same as anaphase in Mitosis • Homologous chromosomes do not separate • Sister chromatids separate • Each chromosome is thus broken down into sister chromatids which move towards either of the poles
  13. 13. Telophase II • Same as telophase in Mitosis • Nuclei are formed. • Cytokinesis occurs. • 4 haploid daughter cells produced. These cells are called as gametes
  14. 14. Meiosis summary
  15. 15. Fertilization • The fusion of a sperm(n) and egg(n) to form a zygote. • A zygote is a fertilized egg (2n) • 2n=diploid, n=haploid

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