The Cell and Inheritance

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The Cell and Inheritance

• In 1903, an American geneticist, named Walter
  Sutton studied the cells of grasshoppers.
• Focused on the movement of chromosomes during the
  formation of sex cells
• Discovered that grasshoppers sex cells have half
  the number of chromosomes as their regular body
  cells.
• One chromosome in each pair came from each
  parent.

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Idea

• Suttons idea came to be
• known as the Chromosome Theory of
• Inheritance.
• Genes are carried from parent to their offspring
  on chromosomes.

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Meiosis

• How do sex cells end up with half the number of
  chromosomes as body cells?
• Meiosis
• Chromosome pairs separate
• They are distributed into 2 different cells
• The resulting sex cells only have half as many
  chromosomes.

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Meiosis

• Before meiosis- every chromosome in the parent
  cell is copied
• Meiosis I-
• chromosome pairs line up in the center
• The pairs separate and move to opposite ends
• 2 cells form, each with half the number of
  chromosomes, each chromosome still has 2
  chromatids

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Meiosis cont.

• Meiosis II-
• The chromosome with their 2 chromatids move to
  the center of the cell
• Centromeres split and chromatids separate, single
  chromosome move to opposite ends of the cell
• End of meiosis- 4 sex cells have been produced,
  each with only half the number of chromosome as
  the parent cell in the beginning

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Line up of Genes

• The human body contains 23 chromosome pairs for a
  total of 46 chromosomes.
• Chromosomes are made up
• of many genes, like beads on
• a string.
• Those 23 pairs of chromosomes
• contains 20,000 to 25,000 genes
• Each gene controls a trait.

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Genetic Principles

1. Traits are passed from one generation to the next
2. Traits are controlled by genes
3. Genes are inherited in pairs, 1 gene from each
   parent

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• 4. Genes can be dominant or recessive
• 5. Dominant genes hide recessive genes
• 6. Some genes are neither dominant nor recessive
  they show incomplete dominance