Th2L03 Human karyotype

Th2L03 Human karyotype

1. 46 chromosomes

   • 23 from each parent
   • 22 pairs of autosomes
   • One pair of sex chromosomes (XX or XY)

2. Assessing chromosomes

   • Staining from metaphase spreads
     • G-banding
       • Chromosomes are stained with Giesma dye to expose light and dark bands
       • Pattern is characteristic for each chromosome pair
   • Cytogenetics
     • study of genetic component of a cell through the visualisation and analysis of chromosomes
     • Human chromosomes are characterised by
       • Size
         • Short arm of chromosome, p
         • Long arm of chromosome, q
       • Pattern of G-bands
       • Location of the centromere
         • Metacentric chromosome
           • Chromosome in which the two chromosome arms are approximately the same length and centromere is located in the middle of the chromosome
             • e.g. chromosome 3
         • Submetacentric chromosome
           • Chromosome in which the centromere is displaced toward one end, producing a short arm and a long arm
             • e.g. chromosome 17
         • Acrocentric chromosome
           • Characterized by the centromere position very near the end of the chromosome with the short arm composed of highly repetitive (satellite) DNA
             • Stalks formed

3. Consequence of abnormal karyotype (out of 1,000,000 conceptions)

   • 850K live births
     • 75K have chromosomal abnormalities
       • 39K trisomics
         • Humans who have gained an extra autosome
           • do not survive development minus a few exceptions on the smallest chromosomes
             • Trisomy 13, 18, 21
       • 13.5K XO
       • 12,750 triploids
         • a polyploid that has three complete haploid sets of chromosomes
       • 4,5 K tetrapolids
         • organisms with 4 haploid chromosome sets
       • 5,2K other
     • 833K children
     • 17K perinatal deaths(around the time of birth)
   • 150K spontaneous abortions

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