BIO207H5 Lecture Notes - Lecture 6: S Phase, Cytokinesis, Cleavage Furrow
Document Summary
Meiosis produces gametes for sexual reproduction: reproduction can be divided into two broad categories. In asexual reproduction, organisms reproduce without mating and produce genetically identical offspring. In sexual reproduction, gametes (reproductive cells) are produced; these unite during fertilization. Multicellular eukaryotes reproduce mainly sexually: males and females carry distinct reproductive tissues and structures, mating requires the production of haploid gametes from both male and female. The union of haploid gametes produces diploid progeny. In meiosis i homologous chromosomes separate from one another, reducing the diploid number of chromosomes to the haploid number. In meiosis ii, sister chromatids separate from one another to produce four haploid gametes, each with one chromosome of the original diploid pair. Three hallmark events occur in meiosis: homologous chromosome pairing, crossing over between homologous chromosomes, segregation (separation) of homologous chromosomes, which reduces chromosomes to the haploid number. Leptotene and zygotene: chromosome condensation begins in leptotene stage. The meiotic spindle forms as microtubules extend out from centrosomes.
