Why does Drosophila have a polytene chromosome?
Polytene chromosomes are a strongly amplified form of interphase chromosomes, found, for example, in salivary gland cells of Drosophila and Chironomus. They arise through many rounds of DNA replication without subsequent separation of daughter chromatids. The chromatids run through the entire length of a chromosome.
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.
How are polytene chromosomes relevant to the Drosophila melanogaster life cycle?
Polytene Chromosomes As the fly larva grows, it keeps the same number of cells, but needs to make much more gene product. The result is that the cells get much bigger and each chromosome divides hundreds of times, but all the strands stay attached to each other.
Where are chromosomes located in Drosophila?
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.
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?
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.
How many pairs of chromosomes are in Drosophila?
It has only four pairs of chromosomes – three autosomes, and one pair of sex chromosomes. Males do not show meiotic recombination, facilitating genetic studies.
How many chromosomes does a housefly have?
| Sr. No. | Name of organism | Chromosome number in meiocyte |
|---|---|---|
| (A) | Human | 42 |
| (B) | Onion | 16 |
| (C) | Housefly | 8 |
| (D) | Rice | 12 |
How are lampbrush chromosomes formed?
Chromosomes transform into the lampbrush form during the diplotene stage of meiotic prophase I due to an active transcription of many genes. They are highly extended meiotic half-bivalents, each consisting of 2 sister chromatids.
What are Polytene and Lampbrush chromosomes?
What do polytene chromosomes do in a fly?
Polytene Chromosomes in Drosophila The fly, Drosophila melanogaster, is a holometabolous insect with four main stages to its lifecycle: embryo, larva, pupa, adult. As a larva, the organism is primarily concerned with obtaining food for the rapid increase in size characteristic of this stage of development.
What are the bands and interbands of polytene chromosomes?
The DNA and protein content of interbands is much lower than that found in bands. Thus, the alternation of compacted and decompacted regions of chromosomes—bands and interbands—appears in polytene chromosomes as black and white transverse stripes ( Fig. 5.13 C). The band/interband pattern of polytene chromosomes is constant.
Why are polytene chromosomes important in the eukaryotic genome?
Polytene chromosomes are considered to be very useful for the analysis of many facets of eukaryotic interphase chromosome organization and the genome as a whole. They develop from the chromosomes of diploid nuclei by successive duplication of each chromosomal element (chromatid).
When was the discovery of the polytene chromosome?
Polytene chromosomes were described in 1881 and since 1934 they have served as an outstanding model for a variety of genetic experiments. Using the polytene chromosomes, numerous biological phenomena were discovered. First the polytene chromosomes served as a model of the interphase chromosomes in general.