Meiosis and Sexual Reproduction: Genetic Variation and Gamete Formation

1. Chapter 7 Meiosis and Sexual Reproduction Section 1: Meiosis Section 2: Sexual Reproduction

2. Section 1 Meiosis Objectives: • Summarize the events that occur during meiosis. • Relate crossing-over, independent assortment, and random fertilization to genetic variation. • Compare spermatogenesis and oogenesis.

3. Section 1 Meiosis Formation of Haploid Cells • Meiosis and Chromosome Number Meiosis reduces the number of chromosomes by half to form reproductive cells. When the reproductive cells unite in fertilization, the normal diploid number is restored. • Meiosis I During Meiosis I, homologous chromosomes separate. Crossing-over during prophase I results in the exchange of genetic material between homologous chromosomes. • Meiosis II During Meiosis II, the two chromatids of each chromosome separate. As a result of meiosis, four haploid cells are produced from one diploid cell.

4. Section 1 Meiosis Meiosis and Genetic Variation • Independent Assortment Independent assortment, the random distribution of homologous chromosomes during meiosis, contributes to genetic variation in sexually reproducing organisms. • Crossing Over and Random Fertilization Both crossing-over and the random fertilization of gametes contribute to genetic variation in sexually reproducing organisms. • Importance of Genetic Variation Genetic variation is essential for evolution to occur.

5. Section 1 Meiosis Meiosis and Gamete Formation • Meiosis in Males In sexually reproducing eukaryotic organisms, gametes form through the process of spermatogenesis in males. • Meiosis in Females In sexually reproducing eukaryotic organisms, gametes form through the process of oogenesis in females.

6. Section 2 Sexual Reproduction Objectives: • Differentiate between asexual and sexual reproduction. • Identify three types of asexual reproduction. • Evaluate the relative genetic and evolutionary advantages and disadvantages of asexual and sexual reproduction. • Differentiate between the three major sexual life cycles found in eukaryotes.

7. Section 2 Sexual Reproduction Meiosis and Gamete Formation • Meiosis in Males In sexually reproducing eukaryotic organisms, gametes form through the process of spermatogenesis in males. • Meiosis in Females In sexually reproducing eukaryotic organisms, gametes form through the process of oogenesis in females.

8. Section 2 Sexual Reproduction Sexual and Asexual Reproduction • Asexual Reproduction Asexual reproduction is the formation of offspring from one parent. The offspring are genetically identical to the parent. • Sexual Reproduction Sexual reproduction is the formation of offspring through the union of gametes from two parents. The offspring are genetically different from their parents. • Types of Asexual Reproduction There are many types of asexual reproduction such as fission, fragmentation, and budding. All types lead to clones of the parent.

9. Section 2 Sexual Reproduction Sexual and Asexual Reproduction continued • Genetic Diversity Whereas sexual reproduction increases variation in the population by making possible genetic recombination, asexual reproduction leads to a lack of genetic diversity among offspring. This lack of diversity is a disadvantage in a changing environment. • Evolution of Sexual Reproduction Sexual reproduction may have begun as a mechanism to repair damaged DNA.

10. Section 2 Sexual Reproduction Sexual Life Cycles in Eukaryotes • Haploid Life Cycle In the haploid life cycle, the simplest of all life cycles, the haploid cell occupies the major portion of the life cycle. • Diploid Life Cycle In the diploid life cycle, the adults are diploid and the diploid individual occupies the major portion of the life cycle. • Alternation of Generations Some organisms have a life cycle that alternates between diploid and haploid phases.