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Prophase (from the Greek πρό, "before" and φάσις, "stage") is the first stage of cell division in both mitosis and meiosis. Beginning after interphase, DNA has already been replicated when the cell enters prophase. The main occurrences in prophase are the condensation of the chromatin and the disappearance of the nucleolus.
A karyotype is the number and appearance of chromosomes in the nucleus of a eukaryotic cell. The term is also used for the complete set of chromosomes in a species or in an individual organism and for a test that detects this complement or measures the number.
Staining is an auxiliary technique used in microscopy to enhance contrast in the microscopic image. Stains and dyes are frequently used in biology and medicine to highlight structures in biological tissues for viewing, often with the aid of different microscopes. Stains may be used to define and examine bulk tissues, cell populations, or organelles within individual cells.
Constitutive heterochromatin domains are regions of DNA found throughout the chromosomes of eukaryotes. The majority of constitutive heterochromatin is found at the pericentromeric regions of chromosomes, but is also found at the telomeres and throughout the chromosomes. In humans there is significantly more constitutive heterochromatin found on chromosomes 1, 9, 16, 19 and Y. Constitutive heterochromatin is composed mainly of high copy number tandem repeats known as satellite repeats, minisatellite and microsatellite repeats, and transposon repeats. In humans these regions account for about 200Mb or 6.5% of the total human genome, but their repeat composition makes them difficult to sequence, so only small regions have been sequenced.
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.
Silver staining is the use of silver to selectively alter the appearance of a target in microscopy of histological sections; in temperature gradient gel electrophoresis; and in polyacrylamide gels.
Torbjörn Oskar Caspersson was a Swedish cytologist and geneticist. He was born in Motala and attended the University of Stockholm, where he studied medicine and biophysics.
Chromosome 21 is one of the 23 pairs of chromosomes in humans. Chromosome 21 is both the smallest human autosome and chromosome, with 48 million nucleotides representing about 1.5 percent of the total DNA in cells. Most people have two copies of chromosome 21, while those with three copies of chromosome 21 have Down syndrome, also called "trisomy 21".
Feulgen stain is a staining technique discovered by Robert Feulgen and used in histology to identify chromosomal material or DNA in cell specimens. It is darkly stained. It depends on acid hydrolysis of DNA, therefore fixating agents using strong acids should be avoided.
Chromosome 3 is one of the 23 pairs of chromosomes in humans. People normally have two copies of this chromosome. Chromosome 3 spans almost 200 million base pairs and represents about 6.5 percent of the total DNA in cells.
Chromosome 7 is one of the 23 pairs of chromosomes in humans. People normally have two copies of this chromosome. Chromosome 7 spans about 159 million base pairs and represents between 5 and 5.5 percent of the total DNA in cells.
Chromosome 10 is one of the 23 pairs of chromosomes in humans. People normally have two copies of this chromosome. Chromosome 10 spans about 133 million base pairs and represents between 4 and 4.5 percent of the total DNA in cells.
Chromosome 12 is one of the 23 pairs of chromosomes in humans. People normally have two copies of this chromosome. Chromosome 12 spans about 133 million base pairs and represents between 4 and 4.5 percent of the total DNA in cells.
Chromosome 14 is one of the 23 pairs of chromosomes in humans. People normally have two copies of this chromosome. Chromosome 14 spans about 107 million base pairs and represents between 3 and 3.5% of the total DNA in cells.
Chromosome 16 is one of the 23 pairs of chromosomes in humans. People normally have two copies of this chromosome. Chromosome 16 spans about 90 million base pairs and represents just under 3% of the total DNA in cells.
Chromosome 18 is one of the 23 pairs of chromosomes in humans. People normally have two copies of this chromosome. Chromosome 18 spans about 80 million base pairs and represents about 2.5 percent of the total DNA in cells.
Chromosome microdissection is a technique that physically removes a large section of DNA from a complete chromosome. The smallest portion of DNA that can be isolated using this method comprises 10 million base pairs - hundreds or thousands of individual genes.
G-banding, G banding, or Giemsa banding is a technique used in cytogenetics to produce a visible karyotype by staining condensed chromosomes. It is useful for identifying genetic diseases through the photographic representation of the entire chromosome complement. The metaphase chromosomes are treated with trypsin and stained with Giemsa stain. Heterochromatic regions, which tend to be rich with adenine and thymine (AT-rich) DNA and relatively gene-poor, stain more darkly in G-banding. In contrast, less condensed chromatin (Euchromatin)—which tends to be rich with guanine and cytosine (GC-rich) and more transcriptionally active—incorporates less Giemsa stain, and these regions appear as light bands in G-banding. The pattern of bands are numbered on each arm of the chromosome from the centromere to the telomere.This numbering system allows any band on the chromosome to be identified and described precisely. The reverse of G‑bands is obtained in R‑banding. Banding can be used to identify chromosomal abnormalities, such as translocations, because there is a unique pattern of light and dark bands for each chromosome.
7-Aminoactinomycin D (7-AAD) is a fluorescent chemical compound with a strong affinity for DNA. It is used as a fluorescent marker for DNA in fluorescence microscopy and flow cytometry. It intercalates in double-stranded DNA, with a high affinity for GC-rich regions, making it useful for chromosome banding studies.
