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Chromosomes. Packaged Instructions for Life. Structure. Chromosomes are packages of DNA wrapped with help of proteins called histones Composed of two identical sister chromatids attached at centromere. Chromosome levels organization: dsDNA Nucleosome Coiled solenoid/nucleosome

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Packaged Instructions for Life

  • Chromosomes are packages of DNA wrapped with help of proteins called histones
    • Composed of two identical sisterchromatidsattached at centromere

Chromosome levels organization:

    • dsDNA
    • Nucleosome
    • Coiled solenoid/nucleosome
    • Chromatin
    • Supercoiled (condensed) chromatin
    • Chromosome

Each sister chromatid contains thousands of identical genes in the same locations on each

    • Gene: segment of DNA that codes for specific proteins
      • Ex: brown hair, green eyes, etc

Gene A

Gene B

Gene C

Gene D

Gene E


Each human somatic or body cell contains two copies of each chromosome

    • 23 sets of chromosomes x 2 = 46 total (other species differ in numbers)
      • Combination of all 23 is TOTAL DNA genome (3 billion base pairs)

One set (23rd) contains sex chromosomes X and/or Y

    • Females have XX
    • Males have XY (Y is just shorter)

Females: XX

Males: XY


Two sets of chromosomes is termed diploid (somatic cells)

  • One set of chromosomes is termed haploid (gametes)
    • Necessary since combination of chromosomes from egg & sperm must be diploid to produce viable (able to live) offspring
      • Fertilized egg = zygote




Diploids have same gene (eye color) but may have different variations (brown vs. blue eyes)

    • called homologouschromatids (similar info)
      • One from mother, one from father

gene for eye color (mom’s brown eyes)

dad’s blue eyes


Map of all 23 sets of chromosomes from a body/somatic cell is called a karyotype

    • Numbered from 1 – 23 based on length, location of centromere, and banding pattern
    • #1-22 are called autosomes, #23 are sex chromosomes

Karyotypes are usually only completed for cases where there might be a chromosomal abnormality

    • Monosomy (missing homolog)
    • Trisomy (Extra homolog)
    • Incorrect sex chromosome numbers
the end
  • Quiz Friday 1/17/14
    • 20 multiple choice