Mieosis 11th

meiosis for 11th standers

1. MEIOSIS By JITESH DAUNDE

2. MEIOSIS Complex type of cell division. Responsible for evolution and diversity Associated with spore formation (Plants and Fungi) Gamets (Animals) Gametes are formed from specialized diploid cells The production of offspring by sexual reproduction includes the fusion of two gametes This specialised kind of cell division that reduces the chromosome number by half results in the production of haploid daughter cells. This kind of division is called meiosis. We come across meiosis during gametogenesis in plants and animals

3. Meiotic events can be grouped under the following phases:

4. longer and more complex. subdivided based on chromosomal behaviour , i.e., i ) Leptotene ii) Zygotene iii) Pachytene iv) Diplotene v) Diakinesis . Crossing over is the exchange of genetic material between two homologous chromosomes. Is an enzyme-mediated process and the enzyme involved is called recombinase . Crossing over leads to recombination of genetic material on the two chromosomes. Meiosis I - Karyokinesis Prophase I

5. The spindle formation is completed Chromosomes move and arrange on the equatorial plane Chromosomal fibres extend from pole towards centromere Metaphase I

6. Chromosomal fibres contract and pull the homologous chromosome. Interchromosomal fibres extend and chromosomes start moving to opposite poles. Homologus chromosomes still attaches to chiasmata , finely get separated called disjunction. At end of this phase half number of chromosomes gather at respective pole. Anaphase I

7. Chromosomes uncoil to form chromatids Spindle disappear Nucleus and nucleolus reappear two daughter nuclei are formed Telophase I

8. Cytokinesis I Division of cytoplasm Plasma membrane constrict in the middle in animal cells Formation of cell plate in plants Formation of two daughter cells with single nucleus consisting single set of chromosomes. Interkinesis - it is a short resting period between meiosis I and meiosis II it may or may not be present

9. It is divided in to sub stages Karyokinesis and cytokinesis Four haploid daughter cells are formed at the end of Meiosis II Meiosis II - Karyokinesis

10. Chromosomes become distinct with chromatids . Nucleolus and nuclear membrane disappear. Prophase II

11. Spindle formation takes place. Chromosomes moves towards the equatorial plane. Chromosomes get connected to respective poles by chromosomal fibres . Metaphase II

12. Centromeres divides and chromatids are separated. Each chromatids now called daughter chromosome. They moves towards respective poles by contraction of chromosomal fibres and elongation of interchromosomal fibres . Anaphase II

13. Daughter chromosomes are gather at respective pole and starts uncoiling Nucleolus reappears and nuclear membrane is formed forming two daughter nuclei. Telophase II

14. Division of cytoplasm forming four haploid daughter cells Cytokinesis II Difference

15. Significance of meiosis Produces haploid gamets for sexual reproduction. Help in maintain chromosomal number constant for given species Introduce genetic recombination leading to variation and evolution Spermatogenesis Oogenesis

16. Thank you