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Chapter 4 DNA, Chromosomes, and Genomes (pg. 202-206, 208-218) Chromosomal DNA and Its Packaging in the Chromatin Fibre Eukaryotic DNA is Packaged into a Set of Chromosomes - The complex of DNA and protein is called chromatin (Greek chroma colour) - The maternal and paternal chromosomes of a pair are called homologous chromosomes - Each human cell contains 46 chromosomes; 22 pairs common to both males and females, plus two so-called sex chromosomes (XY male, XX female) - DNA hybridization is a technique where a labelled nucleic acid strand serves as a probe that localizes a complementary strand o Used to distinguish human chromosomes by painting each one a different colour Painting is typically done during mitosis, when chromosomes are compacted and easy to visualize - The display of the 46 chromosomes at mitosis is called the human karyotype - Cytogeneticists detect chromosome abnormalities associated with inherited defects, and characterize cancers associated with specific chromosome rearrangements in somatic cells by detecting changesin banding patterns or changesin the pattern of chromosomepainting Chromosomes Contain Long Strings of Genes - *Gene segment of DNA containing instructions to make proteins (some make RNA) - Some correlation exists between the complexity of an organism and the number of genes in its genome; Simple bacteria = 500 genesvs. human = 25,000 o However, chromosomes from many eukaryotes (including humans) carry junk DNA that doesnt seem to carry critical information; some of it is useful for the proper expression of certain genes - Although the human genome is 200x that of the yeast S. Cerevisiae, it is 30x smaller than some plants and amphibians, and 200x smaller than a species of amoeba - There is no simple relationship between chromosome number, species complexity, and total genome size The Nucleotide Sequence of the Human Genome Shows How Our Genes Are Arranged - Very little of the human genome codes for proteins; the rest are short, mobile pieces of DNA that have gradually inserted themselves in the chromosome over time (transposable elements)
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