The Cell and Inheritance

1. 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.

2. Idea • Sutton’s idea came to be known as the Chromosome Theory of Inheritance. • Genes are carried from parent to their offspring on chromosomes.

3. 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.

4. 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

5. 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

8. 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.

9. 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

10. 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