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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

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the cell and inheritance
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 grasshopper’s sex cells have half the number of chromosomes as their regular body cells.
    • One chromosome in each pair came from each parent.
  • Sutton’s idea came to be

known as the Chromosome Theory of


    • Genes are carried from parent to their offspring on chromosomes.
  • 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.
  • 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
meiosis cont
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
line up of genes
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.
genetic principles
Genetic Principles
  • Traits are passed from one generation to the next
  • Traits are controlled by genes
  • Genes are inherited in pairs, 1 gene from each parent
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