Question

Briefly describe Prophase I of meiosis.

Answer 1

propose 1 = in comparison to the prophase of mitosis the propose of meiosis I is of longer duration and consist of complex events. during prophase I condensing and thickening of chromosomes division of centresome disappearance of nucleolus and nuclear membrane etc. take place as in prophase of mitosis. the process of exchange of genetic material is called crossing over

Answer 2

Prophase 1 of meiosis 1 has 5 stages.

Leptotene:1}During this phase,the chromatid fibres condense to form chromosomes.

2}Nuclear envelope starts disappearing

Zygotene:1}Pairing between a homologous paternal and maternal chromosome is called synapsis.

2} A complex structure called synaptonemal compleax is formed during this stage.

Pachytene:1} We observe the chromosome as tetrads.

2}In this stage,crossing over begins where exchange of genetic material takes place.

3}Enzyme recombinaise initiates crossing over.

4} By the end of pachytene stage,recombination completes.

Diplotene:1} In diplotene stage the synaptonemal complex starts separating.

2}Chiasmata formation is seen in Diplotene stage.

3}This stage of cell division can last fot several months or years in certain vertebrates.

Diakinesis:1}Chiasmata formation completes and terminates.

2}Chromosome contents become visible.

3}Spindle fibre formation is also seen clearly.

4}Nucleolus and nuclear envelope disappears.