Topic Nuclear Division (Meiosis) Essay - Main Points!

Q) Describe the behaviour of chromosomes during meiosis

Main points
Key idea:	Prophase I
·Chrom condense, form double struc, each comprising of 2 genetically identical sis chromatids ·Homologous chrom pair up, form bivalents ·Chiasmata may form b/w non-sis chromatids ·Result: crossing over - exchange of genetic material b/w homologous chrom
Key idea:	Metaphase I
·Pairs of homologous chrom, guided by spindle attached to centromeres (via kinetochore proteins) move toward metaphase plate of the cell ·Indep assortment where bivalents arrange independently fr each other on metaphase plate ·Ref to possible no of chrom combination: 2n (where n is haploid no)
Key idea:	Anaphase I
·Separation of homologous chrom fr each other (pulled to opp poles of cell) ·due to shortening of spindle attached to their centromeres
Key idea:	Telophase I
·Homologous chrom reach opp poles of cell but may not decondense
Key idea:	Meiosis II (selected stages)
·Metaphase II: chrom line up separately on metaphase plate ·Anaphase II: centromere of each chrom divides, separation of sis chromatids (pulled to opp poles of cell) ·Ref to each separated sis chromatid, with its own centromere, is now a chrom ·Telophase II: chrom decondense to form thread-like indistinct chromatin.
Comments: (i) Visualize the answer with the aid of a labelled diagram. (ii) Verbalize the answer + write down the main points w/o referring to the answer (use abbreviations) (iii) Read again within the next 24h & once more within 72h (do not spend more than 10min) (iv) A common mistake is to describe the behaviour of other non-chromosomal structures (e.g. centrioles, nuclear membrane, etc). This wastes time since no marks will be awarded. (v) In many plants, there is no telophase I or interphase after the first meiotic division. The cell passes straight from anaphase I into prophase II. If there is interphase II, the chromosomes uncoil at telophase I but there is no DNA replication.