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Chromosomes

Chromosomes. During cell division, DNA must be neatly packed into structures called chromosomes Chromosomes- rod shaped structures made of DNA and proteins Contain our genes. Chromosome structure Consists of 2 identical halves Each half- chromatid Each chromatid represents one DNA molecule

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Chromosomes

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  1. Chromosomes • During cell division, DNA must be neatly packed into structures called chromosomes • Chromosomes-rod shaped structures made of DNA and proteins • Contain our genes

  2. Chromosome structure • Consists of 2 identical halves • Each half- chromatid • Each chromatid represents one DNA molecule • Two chromatids of chromosome are attached at a point called a centromere • Chromatin- uncoiled DNA; present in between cell divisions

  3. Chromosome Numbers • Each species has a characteristic number of chromosomes in each cell ( ex: humans = 46; dogs = 78) • Sex Chromosomes- chromosomes that determine sex of organism • Human females have two X chromosomes • Males have one X and one Y chromosome

  4. Autosomes- all other chromosomes in an organism • Every cell has two copies of each autosome, one from each parent • The 2 copies of each autosome called homologous chromosomes • Homologous chromosomes are same size, shape and carry genes for same traits

  5. Chromosome numbers • Karyotype- photomicrograph of chromosomes in a normal dividing human cell

  6. Chromosome numbers • Diploid- cells having 2 sets of chromosomes • 2 autosomes for each homologous pair • 2 sex chromosomes • Abbreviated 2n • In humans, diploid or 2n number is 46- 22 pairs of homologous autosomes and 2 sex chromosomes • Haploid- cells containing only one set of chromosomes (ex. Sperm and egg) • Only one autosome of each homologous pair and only one sex chromosome • Abbreviated - n • n number = 23 in humans

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