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Cell Cycle and Cell Division

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CBSE Gujarat Board Haryana Board

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Class 10 Class 12
Analyse the events during every stage of cell cycle and notice how the following two parameters change.

1. Number of chromosomes per cell.

2. Amount of DNA content (C) per cell.

1.  The number of chromosomes (N) -
It  remains constant throughout the different stages in mitosis It remains 2N throughout the cycle.
However, in meiosis the number of chromosome is reduced to half that is from diploid (2N) to haploid (N). The chromosome number is reduced to half during the anaphase I stage this half number is carried on till the end of meiosis.

2. Amount of DNA (C) -
It becomes double during the interphase stage which is followed by mitosis. This doubling occurs due to the replication of the DNA in the S phase.
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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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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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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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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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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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