Cytogenetics Lecture Notes PDF

CYTOGENETICS LECTURE: Chromosomes DR. SARAH DY HINOGUIN-CASIO SEMI-FINALS CHROMOSOMES - Chromosomes – first observed in tumor cells by Walther Fleming in 1882, 16 years after establishment of genetics....

CYTOGENETICS LECTURE: Chromosomes DR. SARAH DY HINOGUIN-CASIO SEMI-FINALS CHROMOSOMES - Chromosomes – first observed in tumor cells by Walther Fleming in 1882, 16 years after establishment of genetics. Why in tumor cells? - Because in tumor the cells here are fast divide and the mass or tumor is fast growing it’s because of the multiplying cells. If the cells is actively dividing it means we could see a lot active nuclei. Compare and contrast prokaryotic and eukaryotic chromosomes.  Eukaryotic chromosomes EUKARYOTIC CHROMOSOMES  More than one - human chromosomes: 46 (44 autosomes; 2  Linear rather than circular sex chromosomes)  Sequestered within a nucleus  other eukaryotes:  Composed of DNA and globular - fruit fly (2x: 8) proteins (histones) - kingfisher (2x: 132)  Nucleosomes (10 nm diameter beads) - tobacco (4x: 48)  Chromatic (30 nm diameter). A very thin - adder’s tongue fern (2x: 1260) material. Extranuclear DNA: Eukaryotes  Active genes- EUCHROMATIN - Mitochondria, chloroplasts  Inactive DNA – HETEROCHOMATIN - DNAs are circular - Codes for 5% RNA and polypeptides (nonfunctional) required for the organelle replication and function Plasmids  Fungi and protozoa - S. cerevisiae – contains 70 copies of a plasmid (2μm circle) PROKARYOTIC CHROMOSOMES - A prokaryotic chromosome consists of a single molecule of DNA in the form of a closed loop E.g. 1. agrobacterium tumefaciens = 1 linear, 1 circular 2. Vibrio cholerae = 2 circular 3. Bacterial – circular molecule of DNA associated with proteins and RNA - Located in NUCLEOID - Folded into loops that are 50,000 – 100,000 bp AJSE  The parts of a chromosomes:  Telomere – the ends of the chromosomes  Centromere – the primary constriction of the chromosomes; it also divides the chromosome into a short arm (p) and a long arm (q)  Chromatid – a single molecule of DNA PLASMIDS Classification of Chromosomes: - Small, circular molecules of DNA - By size and position of centromere. - Few thousand bp to million bp  Metacentric – centromere in the - Carries information required for replication, cellular traits middle of the chromosome  Submetacentric – centromere divides the chromosome into 1/3 and 2/3  Acrocentric – centromere near the end of the chromosome  Scientists called cytogeneticists can Types of Plasmids recognize and identify many of these gross 1. Fertility (F) factors – chromosomal abnormalities by examining conjugation, transfer of genes chromosomes through a microscope. 2. Resistance (R) factors – carry Cytogeneticists use three things to tell genes for resistance to one or chromosomes apart: more antimicrobial drugs, heavy metals or toxins. 1. Chromosome size 3. Bacteriocin factors – carry 2. The position of the centromere genes for proteinaceous toxins 3. Characteristic banding patterns of (bacteriocin). alternating light and dark bands (caused by 4. Virulence plasmids staining the chromosomes with dyes).  combination, allowing the visualization of the individually colored chromosomes. DETECTION In the “classic” (depicted) karyotype, a dye, 3. Digital karyotyping often Giemsa (G-banding), less frequently - Digital karyotyping is a technique used Quinacrine, is used to stain bands on the to quantify the DNA copy number on a chromosomes. genomic scale. - Giemsa is specific for the phosphate - Short sequences of DNA from specific groups of DNA. Quinacrine binds to the loci all over the genome are isolated adenine-thymine rich regions. and enumerated. - Each chromosome has a characteristic - This is also known as virtual banding pattern that helps to identify them; karyotyping. both chromosomes in a pair will have the same banding pattern. - Karyotypes are arranged with the short arm of the chromosome on top, and the long arm on the bottom. - The short and long arms are called p and q, respectively. - In addition, the differently stained regions and sub-regions are given numerical designations from proximal to distal on the chromosome arms. - Spectral karyotyping is a molecular cytogenetic technique used to simultaneously visualize all the pairs of chromosomes in an organism in different colors. - Fluorescently labeled probes of each chromosome are made by labeling chromosome-specific DNA with different fluorophores. - Because there are a limited number of spectrally-distinct fluorophores, a combinatorial labeling method is used to generate many different colors. - Spectral differences generated by combinatorial labeling are captured and analyzed by using an interferometer attached to a fluorescence microscope. - Image processing software then assigns a pseudo color to each spectrally different