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Section 8.1

Section 8.1. Chromosomes. Chromosome structure. Chromosomes are visible during cell reproduction only Chromatin – the same material in between cell divisions (uncoiled) Each chromosome is made of 2 parts: A single DNA molecule tightly coiled around Proteins called histones.

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Section 8.1

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  1. Section 8.1 Chromosomes

  2. Chromosome structure • Chromosomes are visible during cell reproduction only • Chromatin – the same material in between cell divisions (uncoiled) • Each chromosome is made of 2 parts: • A single DNA molecule tightly coiled around • Proteins called histones

  3. Each chromosome has: • Two identical halves • Each half is called a chromatid • Chromatids are made before cell division • Chromatids are joined close to the center at a spot called the centromere

  4. Chromosome structure

  5. Types of chromosomes • Sex chromosomes – determine the sex of an organism; may also carry other information • In humans sex chromosomes are X and Y • Normal males have XY; normal females have XX • Autosomes – all the other chromosomes (body chromosomes) • In humans there are 44 autosomes (46 total)

  6. Homologous chromosomes • In sexually reproducing organisms, every cell has two copies of each autosome • One copy comes from each parent • These are called homologouschromosomes or homologues • They are the same size and shape, and carry information about the same traits

  7. Karyotypes • A picture of the chromosomes taken during cell reproduction • All the chromosomes are arranged in homologous pairs • Can be used to detect genetic defects, such as incorrect chromosome number

  8. Chromosome number • Diploid cells – 2 sets of chromosomes • 2 of each autosome + 2 sex chromosomes • Represented with 2n (humans n=23; 2n=46) • Haploid cells – 1 set of chromosomes • Only one autosome of each homologous pair + only 1 sex chromosome • Represented with 1n • Egg and sperm cells are haploid  after fertilization the new cell is diploid • All eggs have one X chromosome; sperm have either X or Y  sperm determine the sex of the child

  9. Chromosome number

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