CYTOGENETICS

• Chromosomes carry genes, DNA, and heredity.
• The chromosome is not visible in the active nucleus state due to high H2O content.
• "Chromo" means color, and "Soma" means body.
• Wilhelm Von Waldeyer-Hartz 1st used the term chromosomes in 1888.
• The chromosomes can be counted during metaphase.
• Eduard Adolf Strasburger 1st described chromosomes in 1875.
• Walther Flemming is a German Anatomist whom discovered chromatin, a thread-like structure.
• Euploidy refers to the whole sets of chromosomes in a cell.
• Polyploidy refers to sets of chromosomes that are higher than 46, and is always an exact multiple of haploid number (23 chromosomes).
• Aneuploidy is an abnormality where few chromosomes are involved, and is not a multiple of the haploid number (23 chromosomes).
• There are four types of aneuploidy:

  • Monosomy (2n-1)
  • Trisomy (2n+1)
  • Nullisomy (2n-2)
  • Tetrasomy (2n+2)
• No. of Chromosomes:

  • Mosquito - 6
  • Fruit Fly - 8
  • Onion/Mold - 16
  • Maize/Carrot - 20
  • Tomato/Rice - 24
  • Human - 46
  • Chimpanzee/Tobacco - 48
  • Donkey - 62
  • Horse - 64
  • Dog - 78
• Chromosomes during interphase are long and thin.
• Chromosomes in prophase are decreased in length, and increased thickness.
• Chromosomes during metaphase are short and thick, making it the best phase to observe them.
• Chromosomes during anaphase are smallest and separated.
• Size variation in the chromosomes during mitotic phase of plants

  and animals varies between 0.5u-32u in length and about 0.2u-3.0u in diameter.
• Trillium has the longest metaphase chromosome with a size of 32u.
• Dipterans fly is referred as the giant chromosome with 300u in length and 10u in diameter.
• A karyotype is a photographic representation of chromosomes, arranged in descending order of size.
• The centromere is a primary constriction according to Walther Flemming.
• The centromere is a constricted region that determines the appearance of a chromosome. It is also a region of specialized chromatin and the foundation of kinetochore.
• In a telocentric chromosome, the centromere is located at the end of the cell.
• In an acrocentric chromosome, the centromere is located at the close end and has a satellite in the p-arm.
• In a submetacentric chromosome, the centromere is located between the middle to end of the p-arm.
• The metacentric chromosome has two arms of equal length.
• Chromatids are joined together by a common centromere.
• Sister chromatids are two identical copies of a chromosome held together by their shared centromere.
• The kinetochore is a disk-shaped protein complex made up of 80 or more proteins. This is also where the sister chromatid attaches to the spindle fibers, pulling them apart.
• The telomere is the two ends of the chromosome, required for replication and stability.
• The band refers to the distinguishable part of the chromosome, and may be darker or lighter depending on various binding methods.
• The binding techniques of chromosomes are based on the GC and AT regions, having a consecutive heterochromia region.
• Quinacrine (1958) was found by Casperson.
• Giemsa (1971) was found by Summer.
• Nor (1973) was found by Matsuki and Sasaki.
• Centromeric (1978) was found by Linde and Laursen.
• The Feulgen Staining involves the DNA with 1N HCl, at 60 degrees Celsius, in 10 minutes. This produces a pink color.
• The Q Banding (Quinacrine Mustard) can't stain ends of chromatids, it makes use of fluorescent bands and UV light. This is also similar to G Banding.
• AT region = Dark stain

  GC region = Light stain
• R Banding consists of R bands (from reverse) and makes use of heat treatment and a phosphate buffer followed by Giemsa stain. It's used for finding critical details in the telomere.