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.

Idea

• Sutton’s idea came to be known as the Chromosome Theory of Inheritance.

–Genes are carried from parent to their offspring on chromosomes.

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.

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

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

• 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

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

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