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Text of CYTOGENETICS 2003-2007

Study of chromosomes and related diseases caused by abnormality in its structure and number Study of concepts related to the study of heredity, genetic phenomenon, sex determination and disorders in relation to human inheritance.

HUMAN GENESegment of DNA that codes for a polypeptide.

CHROMATIN composed mainly ofcoiled strands of DNA and its associated histone protein . They represent chromosomes in different degrees of uncoiling

1. DNA 2. Histones 3. DNA binding proteins 4. RNA

HETEROCHROMATIN1. Transcriptionally inactive 2. Highly condensed form 3. Located near centromeres & telomeres 4. Makes up 10% of the chromatin present in an interphase cell 5. DNA replicated late in S phase

EUCHROMATIN1. Transcriptionally active 2. Less condensed ,loosely packed 3. Located near the nuclear pore complex 4. Comprises 90% of chromatin in a interphase cell 5. DNA replicated early in S phase

1. TELOMERES Chromosome tips containing many repeats of the sequence TTAGGG. 2. CENTROMERES- largest constriction of a chromosome ; the site where spindle fibers attach. 3. ORIGIN OF REPLICATION SITES where replicaton fork begin to form

By wrapping around histone proteins and forms compressed loops of DNA

1. TELOCENTRIC - has the centromere at one end 2. ACROCENTRIC - has the centromere near an end of chromosomes 3. SUBMETACENTRIC centromere creates a long q arm and a short p arm 4. METACENTRIC centromere establishes equal sized p and q arms.


Standard chart of chromosomes isolated from a cell at metaphase arranged in order by size and structure or physical landmark

1. Peripheral blood 2. Bone Marrow 3. Cultured skin fibroblasts 4.Amniotic fluid 5. Products of Conception Chorionic villi

1. A sample of blood is drawn and placed in a tube containing heparin as anticoagulant. 2.Through density gradient centrifugation technique, mononuclear cells are isolated are isolated and purified 3. Mononuclear cells are then cultured for 3-4 days in a medium containing phytohemagglutinin. 4. At the end of the culture period, the large population of dividing cells is treated with a drug e.g. Colcemid.

5. The lymphocytes are harvested and treated briefly with a hypotonic solution 6.The swollen cells are fixed, dropped onto a microscope slides, dried and stained to induce a banding pattern . 7. Stained slides are scanned to identify good chromosome spread and they are then photographed. 8. Photos showing images of each chromosomes are cut out and pasted to a backing sheet in an orderly manner.

In doing a full analysis each chromosome is critically compared band-for-band with its homolog.

1. Q BANDING chromosomes are stained with quinacrine 2. G BANDING chromosomes are first digested with trypsin then stained with Giemsa 3. C BANDING chromosomes are treated with acid & base solutions then stained with Giemsa 4. R BANDING Uses olivomycin or acridine orange

A simple cartoon of a chromosomes, often used in genomics to show the over-all physical structure of a chromosomes

GROUP A Chromosomes 1-3 , largest, metacentric chromosomes GROUP B Chromosomes 4-5, large with submedian centromeres GROUP C chromosomes 6-12, medium sized with sub-median centromere GROUP D Chromosomes 13-15, medium sized with acrocentric centromere

GROUP E Chromosomes 16-18, short with median or submedian centromere GROUP F chromosomes 19-20, short with median centromere GROUP G- chromosomes 21-22, very short with acrocentric centromere CHROMOSOME X similar to Group C CHROMOSOME Y similar to Group G