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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
“A well known biologist stated that the life history of an organism can be summed up as gametic fusion, equational division and reductional division.” Comment.

The given statement is correct on the basis of the following facts :

1. The gametic fusion takes place at the time of fertilisation when sperm and ovum fuse to form a diploid zygote.

2. The zygote is divided by mitotic division during its embroynic life and post embryonic life to form a well developed individual.

3. A mature individual produces gametes by gametogensis. Reductional division takes place at this stage and results in the formation of haploid gametes.



 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. 

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.

 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.