Which of the following chromosomes are found in salivary glands of Drosophila?
Polytene chromosomes are a strongly amplified form of interphase chromosomes, found, for example, in salivary gland cells of Drosophila and Chironomus.
How many polytene chromosomes are present in Drosophila?
In Drosophila the degree of polyteny is estimated to be approximately 1024 in salivary gland chromosomes, i.e., about 512 in each homolog. Polyploid chromosomes exhibit a banded structure that is reproducible from individual to individual. In Drosophila there are thousands of recognizable bands.
Which chromosome is Drosophila?
Drosophila flies have both X and Y chromosomes, as well as autosomes. Unlike humans, the Y chromosome does not confer maleness; rather, it encodes genes necessary for making sperm. Sex is instead determined by the ratio of X chromosomes to autosomes.
How polytene chromosomes are formed?
Polytene chromosomes develop from the chromosomes of diploid nuclei by successive duplication of each chromosomal element (chromatid) without their segregation. The newly formed chromatids remain associated lengthwise and together form a cable-like structure, referred to as polytene chromosomes.
What are polytene and Lampbrush chromosomes?
The main difference between polytene and lampbrush chromosome is that polytene chromosomes occur in the salivary glands and other tissues of insects whereas lampbrush chromosomes occur in the oocytes of vertebrates except for mammals and some invertebrates.
How are polytene chromosomes formed in Drosophila?
What is the reason for the presence of polytene chromosomes in salivary glands of Drosophila?
They are produced when repeated rounds of DNA replication without cell division forms a giant chromosome. Thus polytene chromosomes form when multiple rounds of replication produce many sister chromatids which stay fused together.
Where are Drosophila chromosomes located?
These chromosomes are found in several cell types, the function of which is principally secretory. In Drosophila, the most useful are found in the larval salivary glands.
How many chromosomes does Drosophila have?
While drosophila only have a total of 4 chromosomes, they too display sexual dimorphism, with females carrying the double X chromosomes and males carrying XY. The two X chromosomes in female fruit flies, as in mammals, make them a homozygous sex as compared with the XY condition in males, known as heterozygous.
How are polytene chromosomes formed?
Why do polytene chromosomes exist?
What kind of chromosomes are found in the salivary gland?
Salivary gland chromosome (A, B) and mitotic chromosomes (C) of Drosophila melanogaster (redrawn from Swanson : Cytology and Cytogenetics ). How an enormous increase in size of these chromosomes is brought about in salivary glands is not known and various hypotheses are available to explain this issue.
How many chromosomes does the Drosophila pseudoobscura have?
GENERAL CHROMOSOME MORPHOLOGY The chromosome group of Drosophila pseudoobscura, as seen in the spermatogonial, oogonial or nerve cell division, consists of five pairs of chromosomes : V-shaped X chromosome, three rod-shaped autosomes, and one very small dot-like autosome.
What do the bands on a chromosome represent?
The bands occasionally form reversible puffs, known as chromosome puffs or Balbiani rings, which are associated with differential gene activation. The giant chromosomes represent a bundle of fibrils which arise by repeated cycles of endo-reduplication of single chromatids.