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HUMAN CHROMOSOME & KARYOTYPING M. Mansyur Romi CHROMOSOME • The highest order of DNA coiling • Each species has a characteristic number and size of chromosomes, known as karyotype. • The normal number of Xsomes in a nucleus: diploid (2n) • During gametogenesos 2n is halved one of eachpair = haploid (n) Coiling of chromosomal/ nuclear DNA CHROMOSOME – Duplicate themselves before the onset of cell division – Appear during metaphase – After replication each Xsome consist of two identical copies: sister chromatids juncside side by side but still connected at the centromer. CHROMOSOME – Structure: • Centromer (primary constriction) • Long arm (p) • Short arm (q) – Banding patterns: – Heterochromatin: highly condensed – Contains four known genes, its function is not well understood – Flanked to centomers – Euchromatin: more lightly – Contains most of the genes Human kariotype 46,XY Human Genome 23 chromosomes – 60,000 – 70,000 genes – 3 x 109 b.p. – 3,000 c Morgans 1 Chromosome : – 2,000 – 5,000 genes – 1,3 x 108 b.p. – 130 cM 1 Chromosomal microband • 50 – 100 genes • 3x 106 • 3 cM 1/10 Chromosomal microband • ~230 x the length of one globin gene • 1/6 x the length of the duchenne locus TURNER SYNDROME • Karyotipe 45, X • Diidentifikasi pertama kali tahun 1928 oleh Dr. Henry H Turner • Insiden 1/4000 bayi lahir hidup perempuan • Etiologi : Tidak adanya kromosom seks paternal (70%) • Biasanya lethal dalam uterus namun kompatibel dan dapat bertahan setelah kelahiran (99% abortus spontan) Karyotype Turner Macam karyotipe 45, X 50% 46, X, i(Xq) 15% 45, X / 46, XX mosaik 15% 45, X / 46, X, i(Xq) mosaik ~5% 45, X, abnormalitas lain ~5% Gambaran Klinis Turner •Perawakan pendek (rata2 55 inci~137 cm) • Kelainan Kardiovaskular, penyebab tertinggi kematian • IQ normal atau diatas ratarata • Terdapat disgenesis gonada (ovarian dysgenesis) KLINEFELTER SYNDROME • Karyotipe 47, XXY • Variant : 48, XXYY ; 48, XXXY ; 49, XXXXY • Etiologi : error pada : • Paternal Meiosis I • Maternal Meiosis I ~ usia ibu • Maternal Meiosis II • Post zigotic Mitotic ~ Mosaicism • Karena kegagalan rekombinasi Xp / Yp pada pseudoautosomal region • Insiden : 1/1000 bayi laki-laki lahir hidup • Merupakan kelainan kromosom seks pada manusia yang pertama kali dilaporkan Karyotype Klinefelter Kelainan2 pada Klinefelter Syndrome •IQ rata-rata 85 – 90 • Anggota gerak yang panjang dan kurus • Pubertas usia normal namun testis kecil (< 2,5 cm) • Hampir selalu infertil karena kegagalan perkembangan Germ Cell • Kadang-kadang didapatkan ginekomasti • Penurunan produksi testosteron • Juga didapatkan kesulitan belajar, membaca, bahasa, poor social adjustment Karyotipe 47, XYY XYY Syndrome • IQ rata-rata 10-15 point dibawah rata2 • Hiperaktif • Agresif atau sifat psikopatologi bukan gambaran umumnya • Gigi yang besar2, dahi menonjol, telinga panjang, jarijari relatif panjang • Fertilitas normal, pubertas biasanya terlambat sampai 6 bulan Genetic material Gene Mapping Assignment of a locus to a specific chromosome and / or Determining the sequence of genes and their relative distance from one another on a specific chromosome Two types of map: physical map genetic or linkage map GENE STRUCTURE • Promoter: the sequence elements located 5’ to the gene, which fix the site of initiation of transcription and control mRNA quantity and sometimes tissue specificity • Exon: the transcribed regions of the gene that are present in mature mRNA and usually contain coding information. GENE STRUCTURE • Intron: a segment of a gene that is initially transcribed into RNA but is then removed from the primary transcript by splicing together the exon sequences on either side of it. • Enhancers: DNA sequences that act in CIS to increase transcription of a nearby gene. These can act in either orientation 5’ or 3’ to the gene and may act at considerable distance from the gene. CHROMOSOME Xsomes of eukaryotes consist of: • DNA • Histone proteins both are constant and form nucleosome • Nonhistone proteins • RNA both vary with the metabolic activity of the cells