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Chapter 11 Meiosis and Sexual Reproduction Section 1 Reproduction Chapter 11 Section 1: Reproduction Key Vocabulary Terms Adapted from Holt Biology 2008 Meiosis A special process of cell division that results in haploid sex cells The total number of chromosomes decreases to half the original number Gamete A reproductive cell; a haploid reproductive cell that unites with another reproductive cell to form a zygote; Zygote The cell that results from the fusion of gametes (a fertilized egg) Diploid Describes a cell, nucleus, or organism that contains two sets of chromosomes Haploid Describes a cell, nucleus, or organism that has only one set of unpaired chromosomes Homologous Chromosomes Chromosomes that have the same order of genes, the same structure, and that pair during meiosis Chapter 11 Section 1: Reproduction Supplementary Words Adapted from Holt Biology 2008 Chapter 11 Section 1: Reproduction Notes Adapted from Holt Biology 2008 Reproduction Asexual Reproduction - A single parent produces genetically identical offspring Asexual Reproduction Prokaryotes Reproduce by splitting - binary fission Asexual Reproduction Unicellular Eukaryotes Reproduce by mitosis and cytokinesis Asexual Reproduction Multicellular Eukaryotes Reproduce by Fragmentation – sea stars Budding – yeast, hydra Cuttings - plants Parthenogenesis – water fleas, some bees Advantages of Asexual Reproduction Many offspring are produced in a short mount of time. Little energy is required for Gamete production Finding a mate Sexual Reproduction Two parents produce genetically different offspring Sexual Reproduction Background Types of cells: Germ cells – cells that produce gametes Somatic cells – other body cells that do not participate in sexual reproduction Advantages of Sexual Reproduction Genetically diverse populations Variety increases the likelihood that some individuals will survive if the environment changes. Chromosome Number Each chromosome has thousands of genes. Chromosome Number Each species has a certain number of chromosomes. • Mosquitoes = 6 • Chimpanzees = 48 • Humans = 46 • Potato = 48 Human Chromosome Number – Each somatic cell has two sets of 23 chromosomes. – Each gamete has one set of 23 chromosomes. • When fertilization occurs, the zygote will have two sets of 23 chromosomes – one from each gamete. 23 23 + 46 = Haploid and Diploid Cells • Gametes are haploid – Symbol: n • Somatic cells are diploid – Symbol: 2n • For humans, n = 23 2n = 46 Homologous Chromosomes • Paired chromosomes found in diploid cells. Autosomes and Sex Chromosomes Autosomes Chromosomes with genes that do not determine sex Autosomes and Sex Chromosomes Sex chromosomes Chromosomes with genes that determine sex, X and Y in humans –Boys have an X and a Y –Girls have two Xs