Chapter 3, Section 3The Cell and Inheritance

Wednesday, November 11, 2009

Pages 102 -- 106

Objectives

• Describe chromosomes and their role in inheritance.

• Identify and describe the events that occur during meiosis.

Vocabulary Words

• Sperm

• Egg

• Meiosis

Vocabulary Words

• Sperm

• Egg

• Meiosis

Formation of Sex Cells

• Studied by Walter Sutton.

• Sex cells made up of sperm and egg.• Sperm is the male sex cell.• Egg is the female sex cell.

What Walter Sutton Discovered

• Sutton examined the sex cells in many different stages of formation.• Hypothesized that chromosomes were key

to understanding how offspring end up with the traits similar to their parents.

Chromosomes and Inheritance

• With further research, Sutton discovered that each parent contributes only half the chromosomes that are found in each offspring.• Example: The grasshopper has 24

chromosome but the sex cells have only 12.

• Each parent contributes 12 chromosomes.

Theory of Inheritance

• Genes are carried from parents to their offspring on chromosomes.

Meiosis

• Meiosis is the process by which the number of chromosomes is reduced by half to form sex cells -- sperm and eggs.

• During meiosis, the chromosome pairs separate and are distributed to two different cells.

• The resulting sex cells have only half as many chromosomes as the other cells in the organism.

Meiosis and Punnett Squares

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Male Parent

Female Parent

Meiosis

Beginning of meiosis (every chromosome in the cell is copied.

Meiosis I•Chromosome pairs lie up in the center of the cell.•Pairs separate and move to opposite ends of the cell.•2 cells form each with half the number of chromosomes.•Each chromosome is still double stranded.

Meiosis II•Double stranded chromosomes move to the center of the cell.•Centromeres split and two strand of each chromosome split.

End of Meiosis•Four sex cells have been produced.•Each cell has half the number of chromosomes.•Each cell has only one chromosome from each original pair.

Chromosomes

• Chromosomes are made up of many genes joined together like beads on a string.

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Homework

• Workbook 3.3 (due 11/16)

• Vocabulary Quiz 3.3 (on 11/13 for 7B and 11/17 for 7A)