Meiosis

Lesson Objective The student will describe the process of meiosis. Subobjective 1: The student will describe how haploid cells develop into mature gametes. Subobjective 2: The student will compare autosomes to sex chromosomes and body cells to sex cells. Subobjective 3: The student will compare and contrast meiosis I and meiosis II.

Vocabulary Overview 1. Gamete 2. Fertilization 3. Meiosis 4. Sperm 5. Egg

Ticket In! Give an example of a haploid cell. How is a body cell different than a sex cell? List one similarity and one difference between mitosis and meiosis. Click the numbers

Anticipation Guide Meiosis produces genetically identical cells. Diploid cells have twice as many chromosomes as haploid cells. Crossover occurs in Meiosis I only. The autosomes determine the sex of an individual. Meiosis reduces the number of chromosomes in a cell. Erase in the statement boxes

Frayer Model Fill in each box with the relevant information for the given vocabulary word. • Contain DNA • The cells that pass information onto offspring • Sex cells • Females - eggs • Males - sperm Erase inside the boxes

Frayer Model Fill in each box with the relevant information for the given vocabulary word. • The female gamete produced by the ovaries • Used in reproduction • Haploid • One egg arises from meiosis • Ovum Erase inside the boxes

Frayer Model Fill in each box with the relevant information for the given vocabulary word. • Used in reproduction • Haploid • Four sperm arise from meiosis • The male gamete produced in the testes • Sperm cell Erase inside the boxes

Frayer Model Fill in each box with the relevant information for the given vocabulary word. • The fusion of an egg and a sperm • The nuclei in the egg and sperm fuse. • Human egg and sperm combine. Erase inside the boxes

Frayer Model Fill in each box with the relevant information for the given vocabulary word. • The process of dividing diploid cells into haploid cells • Produces genetically identical cells • Essential for sexual reproduction • Takes place only at certain times during the life cycle • Creation of haploid gametes Erase inside the boxes

Body Cells vs. Gametes Body Cells Sex Cells (Gametes) Most of the cells that comprise your body Only the cells that make up eggs and sperm Contain half of a set of chromosomes Contain a complete set of chromosomes These cells are passed onto your children. Not passed onto offspring i.e.: skin cells, brain cells, eyeball cells, kidney cells i.e.: sperm, eggs Of which type of cell is the brain comprised? click the pictures

46 Homologous Chromosomes If you had 23 pairs of socks, how many individual socks would you have? 46 The same is true for the chromosomes in your cells. In each cell, you have 23 pairs of chromosomes called homologous chromosomes. One comes from each parent. They have the same gene but different versions. Are homologous chromosomes completely identical to each other? Why or why not?

Scientists have created a chart that numbers these chromosomes. Homologous Chromosomes Scientists have created a chart that numbers these chromosomes. Erase in the box. What do the different colors on the chromosomes represent? Click here

Autosomes Chromosome pairs 1-22 are not related to the sex of the individual. These chromosomes are responsible for the development and functionality of the organism. They are autosomes. Click here Circle the autosomes.

Sex Chromosomes The 23rd and final pair of chromosomes is called the sex chromosomes. These are not homologous chromosomes. The sex (male or female) and development of sexual characteristics are determined by this set. XX = Female XY = Male Y - smaller sex chromosome responsible for the development of male sexual characteristics such as the testes X: larger sex chromosome contains many genes not directly related to sex characteristics

Diploid vs. Haploid Haploid (n): Diploid (2n): The cell has 1 i.e.: sex cells Haploid (n): The cell has 1 copy of each chromosome i.e.: body cells Diploid (2n): The cell has 2 copies of each chromosome. (homologous chromosomes)

1 + 1 = 1 1/2 + 1/2 = 1 Importance of Meiosis Click here to see examples. This allows for variation within the same species The number of chromosomes is unique to each species. Meiosis reduces the number of chromosomes. Why do our sex cells have to be haploid? To ensure the correct number of chromosomes in the offspring Circle the equation that best represents meiosis. 1 + 1 = 1 1/2 + 1/2 = 1

Chromosomes vs. Chromatids When learning about meiosis, you will hear about chromosomes and chromatids. Do you know the difference? These are attached at the center by a centromere. Each sister chromatid contains the information from just one parent.

Meiosis I Meiosis I: separation of homologous chromosomes Erase above the line. End Result = 2 diploid cells

Nucleus breaks down and centrioles start to produce spindle fibers. Prophase I Nucleus breaks down and centrioles start to produce spindle fibers. Duplicated chromosomes condense and pair up. Crossover occurs and genes are exchanged between homologous chromosomes Can you spot the cell in Prophase I? Answer: F

Click on the globe to watch an educational video online. Crossing Over Click on the globe to watch an educational video online.

Metaphase I These chromosomes are aligned Homologous chromosomes attach to spindle fibers. These chromosomes are aligned along the center so that each side has chromosomes from both parents Chromosomes are aligned randomly to ensure genetic variability. Can you spot the cell in Metaphase I? Answer: E

Anaphase I Homologous chromosomes are pulled apart toward each side of the cell. Sister chromatids stay attached. Can you spot the cell in Anaphase I? Answer: H

Telophase I Spindle fibers break down. Nuclear envelope reforms to contain chromatids. Cytoplasm is divided (cytokinesis). Can you spot the cell in Telophase I? Answer: G

Meiosis II Meiosis II: separation of sister chromatids End Result Erase above the line. End Result click here Result - 4 cells

Same process as Prophase I However, there is no crossover. Can you spot the cell in Prophase II? Answer: I

Metaphase II Same process as Metaphase I. This time, spindle fibers align sister chromatids. Can you spot the cell in Metaphase II? Answer: D

Anaphase II Sister chromatids are separated into each side of the cell. Can you spot the cell in Anaphase II? Answer: B

Telophase II Same process as Telophase I. During cytokinesis, Metaphase II Telophase II Same process as Telophase I. During cytokinesis, the cytoplasm is divided. Which would show the cell after cytokinesis? Can you spot the cell in Telophase II? Answer: C & A

Meiosis I vs. Meiosis II Write the correct term on the line. Then match the picture with the phase. Metaphase I: Prophase II: Anaphase II: Telophase I: Prophase I: Telophase II: Metaphase II: Anaphase I:

Development of Gametes Meiosis produces gametes that are unable to be fertilized. Therefore, they must go through more changes. Spermatogenesis: maturation of sperm Oogenesis: maturation of an egg An egg will always have an X chromosome and a sperm will have an X or a Y. Which gamete is responsible for determining the sex of a child?

Review Questions Which row in the chart below indicates the correct process for each event indicated? A 1 B 3 C 2 D 4 Answer D

Wrap Up Explain why it is important for gametes to be haploid cells.

Teacher's Resources Mitosis Vs .Meiosis Animation Meiosis Animation Mitosis & Meiosis Hangman