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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
Describe significance of meiosis.

Meiosis is very important in the following ways. 

1. Formation of gametes. Meiosis produces gametes in animals for sexual reproduction.

2. Formation of spores. Meiosis produces spores in plants for asexual reproduction.

3. Maintenance of chromosome number. Meiosis reduces the chromosome number in the gametes so that fertilization may restore the original diploid number in the zygote.

4. Introduction of variations. Meiosis provides a chance for the formation of new combinations of alleles and chromosomes. This brings about variations which cause evolution. The new combinations of alleles are produced by crossing-over in prophase-I.


 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.

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

Crossing over takes place during meiosis but not during mitosis.

Name the process in which there is an exchange of genetic material between non-sister chromatids of homologous chromsomes during meiosis.

Crossing over.

 Namethe five phases of of Prophase I.

The five phases of prophase 1 are
i. Leptotene
ii. Zygotene
iii. Pachytene
iv. Diplotene
v.  Diakinesis. 

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.