Chapter 11 Meiosis and Sexual S Section 1: S Gamete: Haploid reproductive cell that unites with another haploid reproductive cell to form a zygote. S Zygote: The cell that results from the fusion of gametes S Diploid: A cell that contains 2 haploid sets (1 full set) of chromosomes S Haploid: A cell that contains 1/2 the full set of chromosomes S Homologous Chromosome: Chromosomes that have the same sequence of genes that have the same structure and that pair during reproduction S : The process of producing offspring I. Asexual Asexual A. A single parent passes a complete copy (diploid) of its genetic information to each of its offspring B. Individual is GENETICALLY IDENTICAL to the parent C. Binary Fission - asexual reproduction of prokaryotic cells D. Fragmentation- reproduction in which the body breaks into several pieces, the pieces regrow missing parts 1
Asexual II. Sexual E. Budding- A new individual splits off from the existing one. F. Parthenogenesis- Process in which the female makes a viable egg that grows into an adult without being fertilized by a male. A. 2 parents give genetic material to produce offspring genetically different from the parents 1. Each parent produces a reproductive cell called a gamete Sexual B. Germ (Sex) Cells and Somatic Cells 2. Gametes join to form a zygote in a process called fertilization. 3. Offspring has traits of both parents because both give gametes 1. Germ (Sex) cells - Cells that are specialized only for reproduction 2. Somatic Cells - All other body cells C. Advantages of Sexual Advantages of Sexual 1. Asexual reproduction is easier and a faster way to reproduce. 2. Sexual reproduction provides variation (differences) in genes 3. Diverse populations are more able to survive environmental change. 4. Less mutation possibilities. 2
III. Chromosome Number Chromosome Number A. Genes are located on chromosomes 1. Each chromosome has thousands of genes that play a role in determining how an organism develops and functions. 2. Each species has a characteristic number of chromosomes. 3. If an organism has too few or too many it won t develop and function properly. Chromosome Number B. Haploid and Diploid Cells 4. Human somatic cells have 46 chromosomes 5. Human sex cells have 23 chromosomes 1. Diploid Cells = somatic cells (2n) 2. Haploid Cells = sex cells (n) C. Homologous Chromosomes Homologous Chromosomes 1. The pair of chromosomes in the diploid set 2. One of each pair of chromosomes comes from one parent 3. Carry different forms of genes 1. Example - mom may give gene for rolling tongue; dad may give gene for not rolling tongue 3
D. Autosomes and Sex Chromosomes Section 2: Meiosis 1. Autosomes - chromosomes with genes that do not determine sex of the individual. 2. Sex Chromosome - X and Y chromosomes that determine sex of individual a. XX = Female b. XY = Male S Meiosis: Form of cell division that produces daughter cells with half the number of chromosomes in one parent cell. S Crossing Over: A process in which genetic material is exchanged between homologous chromosomes Meiosis I. Stages of Meiosis S Independent Assortment: The random distribution of the pairs of genes on different chromosomes to the gametes S Cytokinesis: Cytoplasm division A. A diploid cell goes through 2 divisions to form four haploid cells 1. - Homologous chromosomes are separated 2. I - Sister chromatids of each homologue are separated B. 1. Begins with a diploid cell that has copied its chromosomes 2. Prophase I a. chromosomes condense b. nuclear envelope breaks down c. homologous chromosomes pair d. crossing over occurs (exchange of genetic material) 3. Metaphase I a. Spindle moves pairs of homologous chromosomes to equator of cell 4
3. Anaphase I a. homologous chromosomes separate b. spindle fibers pull chromosomes to opposite poles c. cytokinesis begins 5. Telophase I a. cytokinesis continues C. I I 1. Begins with 2 daughter cells formed from - CHROMOSOMES DO NOT REPLICATE 2. Prophase II a. new spindle form 3. Metaphase II a. chromosomes line up along the equator b. chromosomes attach at their centromeres to spindle fibers I I 4. Anaphase II a. centromeres divide b. chromosomes move to opposite sides of the cell c. cytokinesis begins 5. Telophase II a. nuclear envelope forms around each set of chromosomes b. spindle breaks down c. cell continue cytokinesis 6. Result in 4 haploid cells 5
Comparing Mitosis & Meiosis E. Genetic Variation Types of cell made Genetically Mitosis Cells used for growth; repair; asexual reproduction 2 Identical diploid cells Meiosis Sexual reproduction; occurs in gamete cells 4 Different haploid cells 1. Can help populations survive major environmental change 2. Made possible by sexual reproduction Stages Almost identical with Almost identical with Mitosis 3. Three Key Contributions 4. Crossing Over a. crossing over b. independent assortment c. random fertilization a. happens when one arm of a chromosome crosses over the arm of another b. each chromosome breaks at the point of the crossover and then re-forms its full length with a piece from the other chromosome c. information is no longer identical 5. Independent Assortment 6. Random Fertilization a. random distribution during meiosis b. can line up in either of 2 equally probable ways c. 4 haploid cell have a different assortment in each probability a. fertilization of an egg by a sperm is random b. number of possible outcomes squared c. in humans 2 23 X 2 23 = 70 trillion combinations 6
Section 3: Multicellular Life Cycles S Life Cycle: all of the events in the growth and development of an organism until the organism reaches sexual maturity S Sperm: the male gamete (sex cell) S Ovum: the female gamete (sex cell) I. Diploid Cycle A. Meiosis in sex cells results in the formation of a haploid gamete B. Meiosis and Gamete Formation Meiosis II. Haploid Life Cycle Includes Results in I Which Which separates involves Which separates 4. Homologous Chromosomes 3. Crossing over 5. Chromatids 2. Haploid Cell/ Gamete Which unites during Sexual A. Happens in fungi and protists 1. Meiosis in a diploid zygote results in the formation of the first cell of a multicellular haploid individual III. Alternation of Generations A. Plants and most multicellular protists have a life cycle that alternates between a haploid and a diploid phase 1. Sporophyte - spore producing stage 2. Gametophyte - gamete producing stage 7