13_Meiosis

13_Meiosis - Meiosis and Sexual Life Cycles Chapter 13...

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Unformatted text preview: Meiosis and Sexual Life Cycles Chapter 13 Overview: Variations on a Theme • Living organisms are distinguished by their ability to reproduce their own kind • Genetics is the scientific study of heredity and variation • Heredity is the transmission of traits from one generation to the next • Variation is demonstrated by the differences in appearance that offspring show from parents and siblings Concept 13.1: Offspring acquire genes from parents by inheriting chromosomes • In a literal sense, children do not inherit particular physical traits from their parents • It is genes that are actually inherited Inheritance of Genes ( Y ) • Genes are the units of heredity, and are made up of segments of DNA • Genes are passed to the next generation through reproductive cells called gametes (sperm and eggs) • Each gene has a specific location called a locus on a certain chromosome • Most DNA is packaged into chromosomes • One set of chromosomes is inherited from each parent Comparison of Asexual and Sexual Reproduction • In asexual reproduction , a single individual passes genes to its offspring without the fusion of gametes • A clone is a group of genetically identical individuals from the same parent • In sexual reproduction , two parents give rise to offspring that have unique combinations of genes inherited from the two parents Bud Parent 0.5 mm Concept 13.2: Fertilization and meiosis alternate in sexual life cycles • A life cycle is the generation- to-generation sequence of stages in the reproductive history of an organism Pair of homologous replicated chromosomes Centromere Sister chromatids Metaphase chromosome 5 µm Sets of Chromosomes in Human Cells: somatic cells, homologous chromosomes, sex chromosomes and autosomes Figure 13.3 Pair of homologous duplicated chromosomes Centromere Sister chromatids Metaphase chromosome 5 μ m APPLICATION TECHNIQUE Figure 13.4 Sister chromatids of one duplicated chromosome Key Maternal set of chromosomes ( n = 3) Paternal set of chromosomes ( n = 3) Key 2 n = 6 Centromere Two nonsister chromatids in a homologous pair Pair of homologous chromosomes (one from each set) Diploid Haploid Somatic Gametic Autosome Sex chromosome Homologous Sister Figure 13.5 Key Haploid ( n ) Diploid (2 n ) Egg ( n ) Haploid gametes ( n = 23) Sperm ( n ) Ovary Testis Mitosis and development Diploid zygote (2 n = 46) Multicellular diploid adults (2 n = 46) MEIOSIS FERTILIZATION The Variety of Sexual Life Cycles • The alternation of meiosis and fertilization is common to all organisms that reproduce sexually • The three main types of sexual life cycles differ in the timing of meiosis and fertilization Key Haploid ( n ) Diploid (2...
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13_Meiosis - Meiosis and Sexual Life Cycles Chapter 13...

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