Understanding Polytene Chromosomes in Botany: Study Material for B.Sc. Part II Hons. Paper IV

Polytene chromosomes, giant chromosomes found in salivary glands of insects like fruit flies, exhibit unique banding patterns consisting of bands and interbands. Researchers like Balbiani have studied these chromosomes, noting over 5000 bands in Drosophila. The uncoiling of chromomeres in bands forms swellings called chromosome puffs or Balbiani rings, providing insights into gene arrangements.

• Polytene chromosomes
• Botany
• B.Sc. Hons.
• Genetics
• Chromosome structure

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1. POLYTENE CHROMOSOME Study Material for B.Sc. Part II Botany Hons. Paper IV Dr. Pushpanjali Khare Sr. Asstt. Professor & Head, Deptt. of Botany MMC (PU) Patna

2. POLYTENE CHROMOSOMES Polytene Chromosomes are one of the Giant Chromosomes These are also known as Salivary Gland Chromosomes as they are found in salivary glands of Dipterans (Fruit fly) larvae Exceptional feature: Polytene chromosomes are visible during interphase Polytene chromosomes were first of all observed by Balbiani (1881) in the salivary glands of the non biting midge (lake fly) chironomous Polytene chromosomes have been reported in immature seed tissues (P. vulgaris, P. coccineus) by Nagl in1981 and in anther tapetum of Vigna unguiculata (Guerra and Carvalheira, 1994) In Polytene chromosomes there are several Bands and Interbands representing the heterochromatin and euchromatin regions Bands are regions of high DNA concentration whereas Interbands are regions of low DNA concentration Painter (1933)and Bridges (1936) studied about the close relationships between Band and genes

3. Specific structure of Polytene Chromosome Fig: Polytene chromosomes

4. Structure of Polytene Chromosome Specific features have been observed in the four chromosomes of Drosophila It shows linear series of Bands and Interbands Over 5000 bands have been observed in Polytene chromosomes of Drosophila The Bands of Polytene chromosomes become enlarged due to uncoiling of individual chromomeres in a band which form swellings and are called chromosome puffs or Balbiani rings

6. Detail Structure of Polytene Chromosome

7. Balbiani Rings OR Chromosome Puffs

8. Fig: Balbiani Ring OR Chromosome Puffs

9. Balbiani Rings

10. Balbiani Rings

11. Functional stages of Polytene chromosome

12. The incorporation of radioactively labeled RNA shows the activity of gene (transcription)

13. Functions of Polytene Chromosomes Polytene chromosomes are used as bio-markers

14. Polytene Chromosomes Students are requested to share their queries on Whatsapp group: MMC Botany (D2) OR khare.pushpanjali2@gmail.com OR # 9708063491