Chapter 13 Meiosis and Sexual Life Cycles PowerPoint Lectures for Biology Seventh Edition Neil Campbell and Jane Reece Lectures by Chris Romero Copyright 2005 Pearson Education Inc publishing as Benjamin Cummings Overview Hereditary Similarity and Variation Living organisms Are distinguished by their ability to reproduce their own kind Copyright 2005 Pearson Education Inc publishing as Benjamin Cummings Heredity Is the transmission of traits from one generation to the next Variation Shows that offspring differ somewhat in appearance from parents and siblings Figure 13 1 Copyright 2005 Pearson Education Inc publishing as Benjamin Cummings Genetics Is the scientific study of heredity and hereditary variation Copyright 2005 Pearson Education Inc publishing as Benjamin Cummings Concept 13 1 Offspring acquire genes from parents by inheriting chromosomes Copyright 2005 Pearson Education Inc publishing as Benjamin Cummings Inheritance of Genes Genes Are the units of heredity Are segments of DNA Copyright 2005 Pearson Education Inc publishing as Benjamin Cummings Each gene in an organism s DNA Has a specific locus on a certain chromosome We inherit One set of chromosomes from our mother and one set from our father Copyright 2005 Pearson Education Inc publishing as Benjamin Cummings Comparison of Asexual and Sexual Reproduction In asexual reproduction One parent produces genetically identical offspring by mitosis Parent Bud Figure 13 2 Copyright 2005 Pearson Education Inc publishing as Benjamin Cummings 0 5 mm In sexual reproduction Two parents give rise to offspring that have unique combinations of genes inherited from the two parents Copyright 2005 Pearson Education Inc publishing as Benjamin Cummings 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 Copyright 2005 Pearson Education Inc publishing as Benjamin Cummings Sets of Chromosomes in Human Cells In humans Each somatic cell has 46 chromosomes made up of two sets One set of chromosomes comes from each parent Copyright 2005 Pearson Education Inc publishing as Benjamin Cummings A karyotype Is an ordered visual representation of the chromosomes in a cell Pair of homologous chromosomes Centromere Sister chromatids Figure 13 3 Copyright 2005 Pearson Education Inc publishing as Benjamin Cummings 5 m Figure 13 3 Preparing a Karyotype APPLICATION A karyotype is a display of condensed chromosomes arranged in pairs Karyotyping can be used to screen for abnormal numbers of chromosomes or defective chromosomes associated with certain congenital disorders such as Down syndrome TECHNIQUE Karyotypes are prepared from isolated somatic cells which are treated with a drug to stimulate mitosis and then grown in culture for several days A slide of cells arrested in metaphase is stained and then viewed with a microscope equipped with a digital camera A digital photograph of the chromosomes is entered into a computer and the chromosomes are electronically rearranged into pairs according to size and shape RESULTS This karyotype shows the chromosomes from a normal human male The patterns of stained bands help identify specific chromosomes and parts of chromosomes Although difficult to discern in the karyotype each metaphase chromosome consists of two closely attached sister chromatids see diagram Copyright 2005 Pearson Education Inc publishing as Benjamin Cummings Pair of homologous chromosomes Centromere Sister chromatids 5 m Figure 13 3 Preparation of a human karyotype Layer 2 Figure 13 3 Preparation of a human karyotype Layer 3 Figure 13 3 Preparation of a human karyotype Layer 4 Figure 13 x2 Human female chromosomes shown by bright field G banding Figure 13 x3 Human female karyotype shown by bright field G banding of chromosomes Figure 13 x4 Human male chromosomes shown by bright field G banding Figure 13 x5 Human male karyotype shown by bright field G banding of chromosomes Homologous chromosomes Are the two chromosomes composing a pair Have the same characteristics May also be called autosomes Copyright 2005 Pearson Education Inc publishing as Benjamin Cummings Sex chromosomes Are distinct from each other in their characteristics Are represented as X and Y Determine the sex of the individual XX being female XY being male Copyright 2005 Pearson Education Inc publishing as Benjamin Cummings A diploid cell Has two sets of each of its chromosomes In a human has 46 chromosomes 2n 46 Copyright 2005 Pearson Education Inc publishing as Benjamin Cummings In a cell in which DNA synthesis has occurred All the chromosomes are duplicated and thus each consists of two identical sister chromatids Key Maternal set of chromosomes n 3 2n 6 Paternal set of chromosomes n 3 Two sister chromatids of one replicated chromosome Centromere Figure 13 4 Two nonsister chromatids in a homologous pair Copyright 2005 Pearson Education Inc publishing as Benjamin Cummings Pair of homologous chromosomes one from each set Unlike somatic cells Gametes sperm and egg cells are haploid cells containing only one set of chromosomes Copyright 2005 Pearson Education Inc publishing as Benjamin Cummings Behavior of Chromosome Sets in the Human Life Cycle At sexual maturity The ovaries and testes produce haploid gametes by meiosis Copyright 2005 Pearson Education Inc publishing as Benjamin Cummings During fertilization These gametes sperm and ovum fuse forming a diploid zygote The zygote Develops into an adult organism Copyright 2005 Pearson Education Inc publishing as Benjamin Cummings The human life cycle Key Haploid gametes n 23 Haploid n Diploid 2n Ovum n Sperm Cell n FERTILIZATION MEIOSIS Ovary Testis Mitosis and development Figure 13 5 Multicellular diploid adults 2n 46 Copyright 2005 Pearson Education Inc publishing as Benjamin Cummings Diploid zygote 2n 46 The Variety of Sexual Life Cycles The three main types of sexual life cycles Differ in the timing of meiosis and fertilization Copyright 2005 Pearson Education Inc publishing as Benjamin Cummings In animals Meiosis occurs during gamete formation Gametes are the only haploid cells Key Haploid Diploid n n Gametes n MEIOSIS Zygote 2n Figure 13 6 A Diploid multicellular organism FERTILIZATION 2n Mitosis a Animals Copyright 2005 Pearson Education Inc publishing as Benjamin Cummings Plants and some algae Exhibit an alternation of generations The life cycle includes both diploid and haploid multicellular stages