Chromosomes

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Chromosomes

• (Eukaryotic DNA Structure)

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• When the cell is not dividing, DNA is long and
  stringy and called chromatin.

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• When the cell is dividing, DNA is tightly coiled
  around proteins and is called chromosomes.

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Chromosome Numbers

• Each species has a specific number of chromosomes
  in the nucleus in its cells.

• For example, humans have 46 chromosomes in each
  body cell, dogs have 78 in each body cell.

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Chromosome Numbers

• There is a tongue fern that has 1262 in each body
  cell!
• The number of chromosomes that an organism has is
  NOT related to the complexity of the organism!

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Chromosome Numbers

• In body cells, chromosomes come in pairs.
• Sex chromosomes are the pair of chromosomes that
  determine the sex of the organism.
• In humans, the sex chromosomes are X and Y.
• Normal females have 2 X chromosomes, and normal
  males have 1 X and 1 Y.

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Chromosome Numbers

• All of the other chromosomes are called
  autosomes.
• So, in humans
• 22 pairs or 44 chromosomes are autosomes
• 1 pair or 2 chromosomes are sex chromosomes

There are certain disorders associated with
having too little or too many chromosomes.
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Chromosome Abnormalities

• 1. Down syndrome 3 copies of chromosome 21
  (trisomy 21)

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Chromosomes Abnormalities

• Turner syndrome female with only 1X chromosome
  (XO) (monosomy X)

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Chromosome Abnormalities

• 3. Klinefelter syndrome male with XXY

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Chromosome Abnormalities

• 4. Patau syndrome 3 copies of 13

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• Doctors can detect these conditions before birth
• Amniocentesis removes amniotic fluid from
  around baby
• Chromosomes are photographed and organized onto a
  chart called a karyotype.

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• Chromosomes come in pairs because you inherited
  one copy of the chromosome from your mother and
  on copy of the chromosome from your father.
• The two chromosomes in each pair are called
  homologous chromosomes because they have the same
  size and shape and carry the same genes.

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• Most cells in your body are diploid (2n), which
  means they have 2 sets of chromosomes (one from
  each parent). The diploid number represents how
  many chromosomes are in these cells.

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• Sex cells (a.k.a. gametes, a.k.a. sperm and egg)
  are haploid (n), which means they only have 1 set
  of chromosomes. The haploid number will always
  by half the diploid number.

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Organism of chromosomes in body cells (diploid number) of chromosomes in sex cells (haploid number)
Human 46
Fruit fly 4
Dog 78
Sand dollar 26
Cat 16
Carrot 18
horse 64