Question

Problem 12.4 Describe the structure of giant polytene chromosomes and how they arise Drag the terms on the left to the appropriate blanks on the right to complete the sentences. Reset Help sharp light and dark colorless homologs Polytene chromosomes are formed from numerous DNA pairing of and absence of strand separation or cytoplasmic division. Each chromosome contains about DNA strands in parallel register. They appear in specific tissues, such as salivary glands, of many dipterans such as Drosophila. They appear as comparatively with sections (bands) along their length. Such bands (chromomeres) are useful in chromosome identification, etc. base sequences 10-20 short, thin fibers 1000-5000 long, wide fibers 100-300 replications red and white synthesis large, extended spheres reparations

Answer 1

a) DNA replication

b) Homologs

C) 1000-5000

d)long wide fibres

e)sharp light and dark

Polythene chromosomes are cable like multistandard chromosome made of identical chromatids.

polyteny or many stranded structure is due to replication of DNA several times without nuclear division --Endomitosis.

Consists of alternating dark and light region. Bands are formed by condensation of chromatin reticulum or merging of chromosomes of adjacent chromatids

The cross banding pattern of each polythene chromosome is a constant characteristic within a species and helps in chromosome mapping during cytogenetic studies.

bulging or local swelling of specific bands of polythene chromosomes during certain stages of larval growth in insects is called chromosome puffing.