Chromosomes

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Chromosomes
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DNA STORAGE STRUCTURE

• Eukaryotic cells have their DNA in structures
  called chromosomes stored in the nucleus.

A cells chromosomes
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Chromosome Structure

• Chromosomes
• Contains a single DNA molecule.
• Have the DNA wrapped around proteins called
  histones.

Chromosome structure
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Chromosome condensation

• Chromosomes condense only for cell reproduction.
• Condensation
• Twist
• Become shorter
• Become thicker
• Become visible
• Chromosomes can be moved about cell easier.

Chromosome condensation
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Chromosome replication

• Before cells divide chromosomes replicate so each
  daughter cell has a complete set of DNA.
• Each copy is called a chromatid.
• Sister chromatids are connected by a centromere

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Chromosome pairs

• Chromosomes are arranged in pairs called
  homologous pairs.
• In humans one pair determines sex sex
  chromosomes.
• All other chromosomes are called autosomes.

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Sex Chromosomes

• Either X or Y.
• XX creates female.
• XY creates male.

Sex Chromosomes
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Haploid Vs Diploid

• Haploid Having one of each chromosome. Sperm/
  pollen and egg (gametes)
• Diploid having a pair of chromosomes. All
  cells except gametes have pairs of chromosomes.

Human sperm at the surface of an egg
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Chromosome Numbers

• Each species has characteristic number of
  chromosomes.
• Humans 46
• Fruit flies 8
• Crayfish 200
• Chimpanzee 48

Fruit fly chromosomes
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White board review

1. When DNA replicates what are the copies of the
   chromosomes called?
2. What are the 2 types of chromosome pairs called?
3. What does haploid mean?