Meiosis

1. Premedical- Biology Meiosis

2. Reproduction • The ability to produce new individual organisms, • either asexually from a single parent organism, • or sexually from two parent organisms. • Asexual reproduction • is notlimited to single-celled organisms - most plants • - binary fission- Bacteria • - budding - yeasts and Hydras • - conjugation- bacteria may exchange genetic information • parthogenesis, fragmentation and spore formation • hermaphroditic species can self-fertilize

3. Wingless female giving birth baby hammerhead • Parthenogenesis • lower plants (where it is called apomixis) • invertebrates - water fleas, aphids, some bees and parasitic wasps • vertebrates- some reptiles,fish, and very rarely birds and sharks

4. Sexual reproduction bycombination of genetic material contributed from two different members of the species Each contributes half of the offspring's genetic material male produce sperm or microsporein anisogamous species andfemale produce ovum or megaspore In isogamous species the gametes are similar or identical in form, but may have separable properties and then may be given other different names.

5. Sexually reproducing organisms • have two sets of genes for every trait • called alleles,offspring inherit one allele from each parent • the offspring is combination of parental genes • diploid and haploid phases alternation in cell lines • inbreeding = is the reproduction from the mating • of two genetically related parents • inbred line – origin of homozygote offsprings by sexual reproduction

6. Human life cycle

7. Meoisis = division of germ cells -reduction of diploid chromosomal number to haploid - origin of haploid gamets

10. First meiotic division • n • M I = reduction2n = heterotypic • n • Prophase I: • leptotene– spiralisation of chromosomes • zygotene– pairing of homologous chromosomes – • synapsis -bivalents • synaptonemal complex

11. Synaptonemal komplex = three levels of protein structure

12. 3. pachytene – each chromosome has two chromatids – tetrads crossing-over = reciprocal exchange of homologous parts of non-sister chromatids = recombination of maternal and paternal genetic material Recombination possibilities between non-sister chromatids and result products- two chiasmata on one bivalent a - recombination only between 2 chromatids; b - 4 chromatids in recombination; c - 3 chromatids in recombination.

13. 4. diplotene – separation of homologs connection only in sites of chiasmata, prerequisite of crossing-over = chiasma formation 5. diakinesis – terminalisation of chiasmata maximal contraction of chromosomes Metaphase I – bivalents in equatorial plane of the cell without splitting of centromers

14. Anaphase I– migration of homologous chromosomes to the opposite poles - randomly according their parental origin Telophase I- chromosomes to the opposite sides Cytokinesis – division of cytoplasm- equal in spermiogenesis, unequal in oogenesis Interkinesis – without replication, abbreviated interphase

15. Second meiotic division n M II – homeotypic n = mitotic division n inProphase II division and separation of centriols - mitotic spindle in Metaphase II splitting of centromers in Anaphase II separation of chromatids

16. Gametogenesis • – formation of gametes • migration of primordial germ cells to the gonads • during early fetal development number of mitotic division

17. Spermatogenesis in the time of sexual maturity (top off testosteron threshold) – continuous process growth MI mitotic division - spermatogonia primary spermatocyte (dipl) M II 2 secondary spermatocytes (hapl) 4 spermatids diferentiation-spermiogenesis 4 sperm 1 cycle = about 10 weeks

19. Oogenesis M I to the end of prophase 3 month of fetal life diplotene=dictyotene growth at the time of birth Oogonia primary oocyte (dipl) mitotic division in the time of sexual maturity M II M I continued secondary oocyte ovulation in metaphase II +1st polar body anaphase II + telophase II only after fertilization oocyte + 2nd polar body

21. prenatal oogonia Mitotic division growth 3rd month of fetal life - Dictyotene MI - division stops at time of birth primary oocyte M I meiosis 1st polar body Sexual maturity- Metaphase MII - ovulation M II secondary oocyte Sexual maturity 2nd polar body egg cell Anaphase II, Telophase II only after fertilization Fertilization – pronucleus Ovum after MII- pronucleus zygote Oogenesis

22. Oogenesis a fertilization I. meiotic division polar body oogonia primary secondary oocyte n 2n fertilization a II. Meiotic division

23. Differences in gametogenesis Male Female Initiation Puberty Early embryonic life Duration cca 72 days 10-50 years Numbers of mitoses 30 - 500 20-30 in gamete formation Gamete production 4 spermatids 1 ovum+3 polar bodies Gamete production 100-200 million 1 ovum per menstrual per ejaculate cycle

25. Consequences of meiosis • reduction of diploid chromosomal number to haploid • segregation of alleles in M I, M II (2st Mendel´s law) • 3. random assortment of homologues – random combination maternal and paternal chromosomes in gametes (3nd Mendel´s law) • 4. increase of genetic variability by crossing over (chromatids with segments of maternal and paternal origin)

26. Genetic determination of sex 23,X 23,X 23,Y

27. If you feel small, low-spirited and useless, remember: Thanks to perfect Ovum and the fastest Sperm and their genetic information, YOU ARE ABSOLUTELY UNIQUE and NO REPEATABLE ELEMENT THE WHOLE UNIVERSE

28. Thank you for your attention Campbell, Neil A., Reece, Jane B., Cain Michael L., Jackson, Robert B., Minorsky, Peter V., Biology, Benjamin-Cummings Publishing Company, 1996 –2010.