Principle of Inheritance and VariationMediumBloom L3
Question
The salivary gland chromosomes in the dipteran larvae, are useful in gene mapping because: [2005]
Options
A.these are fused
B.these are much longer in size
C.these are easy to stain
D.They have endoreduplicated chromosomes.
Solution
Sol.(d) [Key Concept: Polytene Chromosomes — Gene Mapping] Salivary gland chromosomes (polytene chromosomes) in Drosophila larvae are useful in gene mapping because they have ENDOREDUPLICATED chromosomes — the DNA has been replicated repeatedly (up to 1000-16000 times) without cell division, producing giant chromosomes visible under light microscopy. They show distinct banding patterns (chromomeres) that serve as physical landmarks for gene mapping. They were first described by Balbiani (1881) and reach lengths of 200 μm.
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