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Cell Cycle and Cell Division

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Class 10 Class 12
Why is meiosis essential in sexually reproducing organisms ?

Meiosis is the reduction division which  reduces the number of chromosomes to half in gametes formed in sex organs. Thus it is necessary for attaining haploid number of chromosomes in gametes. These gametes then fuse and restore the chromosome number in the organisms. Thus, meiosis is necessary for the maintenance of chromosome number.
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Namethe five phases of of Prophase I.

The five phases of prophase 1 are
i. Leptotene
ii. Zygotene
iii. Pachytene
iv. Diplotene
v.  Diakinesis.
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What are two types of cells on the basis of presence or absence of nucleus ?

On the basis of the presence and absence of nucleus the cells are divided into two types Eukaryotic and prokaryotic cells.
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Name the process in which there is an exchange of genetic material between non-sister chromatids of homologous chromsomes during meiosis.

Crossing over.
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Name an important event that occurs during meiosis and not during mitosis.

Crossing over takes place during meiosis but not during mitosis.
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What is polyteny ?

Polytene chromosomes are giant chromosomes which are formed due to repeated DNA replication without cell division. They are found in some insects.
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