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Unformatted text preview: 1 April 24, 2008 April 24, 2008 Biology 113, Lecture 9 Biology 113, Lecture 9 Concepts: 13.1, 13.2 and 13.3 Part 1 Part 1 - Overview Overview • A¡brief¡introduction to heredity • Role of meiosis in sexual life cycles • Origins of genetic variation Meiosis and Sexual Life Cycles - Chapter 13 Overview: Hereditary Similarity & Variation Overview: Hereditary Similarity & Variation • Living organisms are distinguished by their ability to reproduce their own kind • Heredity is the transmission of traits from one generation to the next • Variation shows that offspring differ in appearance from parents and siblings • Genetics is the scientific study of heredity and variation Inheritance of Genes Inheritance of Genes • Physical traits of offspring come for inheritance of genes (segments of DNA that represent the basic units of heredity) • Each gene has a specific locus on a certain chromosome • One set of chromosomes is inherited from each parent (diploid cells contain both sets) • In sexual reproduction, cells called gametes (sperm and eggs) (each containing one set) unite, passing genes to the next generation Asexual and Sexual Reproduction Asexual and Sexual Reproduction • In asexual reproduction, one parent produces genetically identical offspring by mitosis • In sexual reproduction, two parents give rise to offspring that have unique combinations of genes inherited from the two parents Asexual reproduction in hydra Asexual reproduction in hydra – via via “budding budding ” Parent Bud • Form of “cloning” • Offspring bud from parent • Involves mitosis • Offspring is genetically identical to parent • Variation can only occur following mutation (a change in a gene) Figure 13.2 Fertilization and meiosis alternate in Fertilization and meiosis alternate in sexual life cycles sexual life cycles • A life cycle is the generation-to-generation sequence of stages in the reproductive history of an organism, from conception to production of its own offspring • Track the behavior of chromosomes through the sexual life cycle. • Begin with an audit of the chromosome count. 2 Sets of Chromosomes in Human Cells Sets of Chromosomes in Human Cells • Each human somatic cell (any cell other than a gamete ) has 46 chromosomes arranged in pairs • A karyotype is an ordered display of the pairs of chromosomes from a cell • The two chromosomes in each pair are called homologous chromosomes , or homologues • Both chromosomes in a pair carry genes controlling the same inherited characteristics 5 μm Pair of homologous chromosomes (one from each parent) Sister chromatids (duplicated chromosome)...
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This note was uploaded on 04/29/2008 for the course BIO 113 taught by Professor Swenson during the Spring '08 term at Ohio State.
- Spring '08