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.
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Do polytene chromosomes show somatic pairing?
Polytene chromosomes show somatic pairing, wherein homologous chromosomes remain associated with each other side by side. Polytene chromosomes increase the cell volume and expand the cell. They also show a high level of gene expression due to multiple copies of the genes.
What is the purpose of a polytene chromosome?
Polytene chromosomes are large chromosomes which have thousands of DNA strands. They provide a high level of function in certain tissues such as salivary glands of insects.
What are polytene chromosomes and where they found?
Polytene chromosomes are formed when the products of multiple rounds of S-phase remain tightly associated to form one supersized chromosome. In particular polytene chromosomes are found in a specific subset of endopolyploid cells, which have undergone a variant cell cycle known as the endocycle.
Why do fruit fly larvae need polytene chromosomes?
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.
Are polytene chromosomes haploid or diploid?
The end product of the replication cycles is a nucleus with a haploid number of chromosomes, each containing up to 2,000 or more parallel strands. In the Collembola, however, the polytene chromosomes typically remain unpaired and the nuclei contain the diploid number (Fig. 92).
What is meant by somatic pairing?
Ans: Somatic pairing is the pairing of homologous chromosomes during mitosis in a somatic cell (body cell other than sex cells). The salivary gland chromosome is also known as polytene chromosomes.
What is a puff in a polytene chromosome?
Chromosome puffs refer to the diffused and uncoiled regions present within the polytene chromosome which are a site for transcription of RNA and synthesis of proteins as it contains concentrated RNA polymerase enzyme.
What is meant by Chromocenter in a polytene chromosome?
polytene chromosome chromocenter A region at which the centric regions of polytene chromosomes are joined together.
How are polytene chromosomes prepared?
Polytene chromosome squash preparation: Rinse larvae with water and transfer to PBS in a tissue culture dish for dissection. Grasp the tip of the mouth hooks with one pair of forceps, hold the body about 2/3 of the way down with the other pair, and pull on the mouth hooks so the salivary glands are exposed.
Why is acetic acid used in polytene chromosomes?
Acetic acid is another popular non-coagulative fixative component known for its swelling affect on tissues [15] that in the case of polytene chromosome squashes helps to accommodate stretching of the chromatin in the interband regions [20].
Which organ is generally used to find the polytene chromosome in Drosophila?
Polytene chromosomes are a strongly amplified form of interphase chromosomes, found, for example, in salivary gland cells of Drosophila and Chironomus.
How many arms are present in polytene chromosome?
It is a giant chromosome with 5 long and 2 short arm radiating from a central point called chromocentre. It is 2000 ฮผm in length (7.5 ฮผm in somatic cells).
Which is the technique of physical mapping?
The three basic varieties of physical mapping are fluorescent in situ hybridization (FISH), restriction site mapping and sequencing by clones.
What is polytene and lampbrush chromosome?
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.
Why are polytene chromosomes so large what has happened to these Drosophila chromosomes to make them so easily visible under the microscope?
Because polytene chromosomes are extended and consist of so much DNA, they are easily visible under the light microscope. A useful feature of these chromosomes is that they have a pattern of dark and light bands, like a bar code, which is unique for each chromosome.
Who discovered polytene chromosome?
Solution : Polytene chromosomes were first time discovered by the Italian cytologist EG Balbiani (1881) in the salivary gland cells of Chironomus larva.
How are giant chromosomes produced?
Polytene chromosomes are giant chromosomes also called salivary chromosomes as it was found in the salivary gland of Chironomus and Drosophila. Polytene chromosomes are formed by somatic pairing of homologous chromosomes followed by their repeated replication or endomitosis. They are in permanent prophase.
Which chromosome has highest DNA content?
Chromosome 1 is the largest human chromosome, spanning about 249 million DNA building blocks (base pairs) and representing approximately 8 percent of the total DNA in cells.
What is the difference between haploid and monoploid?
The haploid number is the number of chromosomes in a gamete of an individual. This is distinct from the monoploid number which is the number of unique chromosomes in a single complete set. In humans, the monoploid number (x) equals the haploid number (the number in a gamete, n), that is, x = n = 23.
Can there be DNA replication without cell division?
Yes, there can be DNA replication without involvement of cell division in a cell and one such condition existential is called as ‘Polyteny. Polyteny basically occurs because of failure of separation of replicated strands of DNA repeatedly.
What made you pair 2 chromosomes together?
The two identical chromosomes that result from DNA replication are referred to as sister chromatids. Sister chromatids are held together by proteins at a region of the chromosome called the centromere. Chromosomes undergo additional compaction at the beginning of mitosis.
Are chromosome pairs joined?
The two copies of a chromosome are called sister chromatids. The sister chromatids are identical to one another and are attached to each other by proteins called cohesins.
How are chromosomes paired What is the process called?
Homologous chromosomes pair in a process called as synapsis during zygotene phase of prophase I of meiosis I. It allows matching-up of homologous pairs prior to their segregation and possible chromosomal crossover between them.
How is a polytene chromosome different from a normal chromosome quizlet?
A polytene chromosome contains banding patterns and is large because of repeated replications of DNA without nuclear division. In what way do polytene chromosomes differ from other chromosomes? Polytene chromosomes are replicated but not separated.