Question

5 stages of prophase in mieosis 1

Answer 1

Answer:

Explanation:

changes a cell undergoes during the following stages are −

Leptotene

Also called thin-threaded stage.

Volume of nucleus increases.

Formation of aster.

Condensation of nuclear chromatin by dehydration.

Chromosome appears long thread like and made of two sister chromatids.

Thin-threaded Stage

Zygotene

Also called yoked-threaded stage.

Pairing of homologous chromosomes occurs. This is called synapsis or syndesis.

Formation of bivalents.

Pairing of homologous chromosomes in a zipper-fashion.

Yoked-threaded Stage

Pachytene

Also called thick-threaded stage.

Further condensation of chromosomes.

Sister chromatids are visible which are joined at the centromere and is known as dyad.

Crossing over occurs between two non-sister chromatids of homologous chromosomes.

Crossing over is regulated by recombinase enzyme.

Thick-threaded Stage

Diplotene

Called double threaded stage.

Longest duration.

Nuclear membrane and nucleoli start disappearing.

The homologous chromosomes start separating.

The point of attachment or crossing over is known as chiasmata.

The chiasmata starts moving towards the ends of chromosomes called terminalisation.

Double-threaded Stage

Diakinesis

Terminalisation is completed.

The non-sister chromatids remain in contact with each other at the telomeres.

Complete disappearance of nuclear membrane and nucleoli.

Diakinesis

Answer 2

Answer for Class 11 Biology Students

Stages of Prophase I is the longest phase and is divided into 5 sub stages:

Leptotene:

 Chromosomes gradually become visible under microscope as slender threads.

 Condensation of chromatin fibres continues.

 Centrioles move a part.

 Spindle begins to develop.

Zygotene: Homologous chromosomes  come to lie side by side in pairs, the process is called Synapsis. Pairing is so through that all the corresponding points (genes) lie exactly opposite to each other. A pair of homologous chromosomes lying together is known as bivalent or tetrad. A fibrillar organelle called synaptonemal complex develops between the synapsed homologous chromosomes.

Pachytene:

 This stage is characterized by appearance of recombination nodules, the sites at which crossing over occurs between non sisters chromatids of homologous chromosomes.

 Crossing over is the exchange of genetic material between two homologous chromosomes. It occurs by breakage and reunion of chromatid segment.

 Breaking of chromatid segment is assisted by endonuclease enzyme while union of chromatid segment is aided by ligase enzyme. Complex of these enzymes is collectively called recombinase enzyme.

Note: Crossing over leads to recombination of genetic material on two chromosomes.

Diplotene:

 Dissolution of synaptonemal complex results in separation of homologous chromosomes of bivalents, except at the sites of crossovers. The process of separation of homologous chromosomes is called disjunction.

 X-shaped structures so formed are called chiasmata.

Diakinesis:

 The chiasmata disappear by sliding towards the tips of chromosomes; the process is called terminalization.

 Nucleolus and nuclear membrane disintegrate.

 Chromosomes lie free in cytoplasm.

Note: A mnemonic in hindi “Lata Zara Paani De Dena”.

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