Lesson 1 Sexual Reproduction and Meiosis

Transcription

1 Lesson 1 Name Date Class A. What is sexual reproduction? 1. produces an offspring when genetic materials from two different sex cells combine. a. The female sex cell, a(n), forms in an ovary. b. The male sex cell, a(n), forms in a testis. 2. During a process called, an egg cell and a sperm cell join together. The new cell that forms is called a(n). B. Diploid Cells 1. Organisms that reproduce sexually make two kinds of cells cells and sex cells. 2. Body cells are ; they have pairs of chromosomes. 3. If a zygote has too many or too few, it will not develop properly. 4. Different organisms have different of chromosomes. 5. are pairs of chromosomes that have genes for the same traits arranged in the same order. C. Haploid Cells 1. Sex cells are ; they have only one chromosome from each pair of chromosomes. 2. In, one diploid cell divides and makes four haploid cells. D. The Phases of Meiosis 1. Meiosis involves two divisions of the nucleus and the. These divisions, known as meiosis I and meiosis II, result in four haploid cells. 2. During, the reproductive cell grows and duplicates its chromosomes. 3. During meiosis I, each pair of duplicated homologous chromosomes. 4. After meiosis I, the two cells formed during this stage go through a second division of the sister and cytoplasm called meiosis II. During meiosis II, separate to produce four haploid cells. 10 Reproduction of Organisms

2 Lesson Outline continued E. Why is meiosis important? 1. Meiosis forms sex cells with the correct haploid number of. This maintains the correct number of chromosomes in organisms when sex cells join. 2. Meiosis creates genetic variation by producing cells. F. How do mitosis and meiosis differ? 1. During and cell division, a body cell and its nucleus divide once and produce two identical cells. 2. During, a reproductive cell and its nucleus divide twice and produce four cells two pairs of identical haploid cells. G. Advantages of Sexual Reproduction 1. Sexual reproduction produces that have a new combination of DNA. This results in genetic individuals. 2. Genetic variation gives individuals within a population slight differences that might be an advantage if the changes. 3. breeding has been used to develop desirable traits in plants and animals. H. Disadvantages of Sexual Reproduction among 1. One disadvantage of sexual reproduction is that organisms have to grow and develop until they are mature enough to produce cells. 2. Another disadvantage is that searching for a mate takes time and energy and might expose individuals to predators,, or harsh environmental conditions. Reproduction of Organisms 11

3 MiniLab LESSON 1: 20 minutes How does one cell produce four cells? When a diploid cell goes through meiosis, it produces four haploid cells. How does this happen? Procedure 1. Read and complete a lab safety form. 2. Make a copy of the diagram by tracing circles around a jar lid on your paper. Label as shown. 3. Use chenille craft wires to make red and blue duplicated chromosomes 2.5 cm long and green and yellow duplicated chromosomes 1.5 cm long. Recall that a duplicated chromosome has two sister chromatids connected at the centromere. 4. Place the chromosomes in the diploid cell. 5. Move one long chromosome and one short chromosome into each of the middle cells. 6. Separate the two strands of the chromosomes, and place one strand into each of the haploid cells. Analyze and Conclude 1. Describe What happened to the chromosomes during meiosis I? During meiosis II? 2. Think Critically Why are two haploid cells (sperm and egg) needed to form a zygote? 3. Key Concept How does one cell form four cells during meiosis? 12 Reproduction of Organisms

4 Content Practice A Directions: On the line before each definition, write the letter of the term that matches it correctly. Each term is used only once. 1. production of an offspring through the combination of egg and sperm 2. female sex cell 3. male sex cell 4. joining of egg and sperm 5. the cell formed by fertilization A. diploid cell B. egg C. fertilization D. haploid cell E. homologous chromosomes F. meiosis G. sexual reproduction H. sperm I. zygote LESSON 1 6. body cell or zygote, which has pairs of chromosomes 7. male or female sex cell that has only one chromosome from each pair 8. process by which one diploid cell divides into four haploid cells 9. two chromosomes that have genes for the same traits in the same order Directions: On the line before each statement, write T if the statement is true or F if the statement is false. 10. Sexual reproduction produces offspring that is identical to the parents. 11. The nucleus divides in meiosis I and again in meiosis II. 12. During meiosis, the number of chromosomes in each cell stays the same. Reproduction of Organisms 13

5 Key Concept Builder LESSON 1 Key Concept What is sexual reproduction, and why is it beneficial? Directions: Work with a partner to answer each question or respond to each statement on the lines provided. 1. Name the type of reproduction that occurs when the genetic materials from two different cells combine to produce an offspring. 2. What are egg cells? 3. What are sperm cells? 4. Explain the relationship between fertilization and a zygote. 5. What happens to a zygote? 6. Compare the DNA of an offspring to the DNA of its parents. 7. Why do offspring from the same parents usually have a different set of traits? Reproduction of Organisms 1