Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings PowerPoint Lectures for Biology, Seventh Edition Neil Campbell and Jane Reece Lectures by Chris Romero Chapter 21 The Genetic Basis of Development

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Overview: From Single Cell to Multicellular Organism Genetic analysis and DNA technology have revolutionized the study of development Researchers use mutations to deduce developmental pathways They apply concepts and tools of molecular genetics to the study of developmental biology

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

When the primary research goal is to understand broad biological principles, the organism chosen for study is called a model organism Researchers select model organisms that are representative of a larger group, suitable for the questions under investigation, and easy to grow in the lab Video: C. elegans Crawling Video: C. elegans Crawling

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Concept 21.1: Embryonic development involves cell division, cell differentiation, and morphogenesis In embryonic development of most organisms, a single-celled zygote gives rise to cells of many different types, each with a different structure and corresponding function Development involves three processes: cell division, cell differentiation, and morphogenesis (“creation of form”)

LE 21-3 Fertilized egg of a frogTadpole hatching from egg

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Through a succession of mitotic cell divisions, the zygote gives rise to a large number of cells In cell differentiation, cells become specialized in structure and function Morphogenesis encompasses the processes that give shape to the organism and its various parts

LE 21-4 Animal development Zygote (fertilized egg) Eight cellsBlastula (cross section) Gastrula (cross section) Adult animal (sea star) Cell movement Gut Cell division Morphogenesis Observable cell differentiation Seed leaves Shoot apical meristem Root apical meristem Plant Embryo inside seed Two cells Zygote (fertilized egg) Plant development

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Concept 21.2: Different cell types result from differential gene expression in cells with the same DNA Differences between cells in a multicellular organism come almost entirely from gene expression, not differences in the cells’ genomes These differences arise during development, as regulatory mechanisms turn genes off and on

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Evidence for Genomic Equivalence Many experiments support the conclusion that nearly all cells of an organism have genomic equivalence (the same genes) A key question that emerges is whether genes are irreversibly inactivated during differentiation

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Totipotency in Plants One experimental approach for testing genomic equivalence is to see whether a differentiated cell can generate a whole organism A totipotent cell is one that can generate a complete new organism Cloning is using one or more somatic cells from a multicellular organism to make a genetically identical individual

LE 21-5 Transverse section of carrot root 2-mg fragments Fragments cul- tured in nutrient medium; stir- ring causes single cells to shear off into liquid. Single cells free in suspension begin to divide. Embryonic plant develops from a cultured single cell. Plantlet is cul- tured on agar medium. Later it is planted in soil. A single somatic (nonreproductive) carrot cell developed into a mature carrot plant. The new plant was a genetic duplicate (clone) of the parent plant. Adult plant

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Nuclear Transplantation in Animals In nuclear transplantation, the nucleus of an unfertilized egg cell or zygote is replaced with the nucleus of a differentiated cell Experiments with frog embryos have shown that a transplanted nucleus can often support normal development of the egg

LE 21-6 Frog embryoFrog egg cellFrog tadpole UV Less differ- entiated cell Donor nucleus trans- planted Enucleated egg cell Most develop into tadpoles <2% develop into tadpoles Donor nucleus trans- planted Fully differ- entiated (intestinal) cell

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Reproductive Cloning of Mammals In 1997, Scottish researchers announced the birth of Dolly, a lamb cloned from an adult sheep by nuclear transplantation from a differentiated mammary cell Dolly’s premature death in 2003, as well as her arthritis, led to speculation that her cells were “older” than those of a normal sheep, possibly reflecting incomplete reprogramming of the original transplanted nucleus

LE 21-7 Mammary cell donor Egg cell donor Egg cell from ovary Nucleus removed Cells fused Cultured mammary cells are semistarved, arresting the cell cycle and causing dedifferentiation Nucleus from mammary cell Early embryo Grown in culture Implanted in uterus of a third sheep Surrogate mother Embryonic development Lamb (“Dolly”) genetically identical to mammary cell donor

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Since 1997, cloning has been demonstrated in many mammals, including mice, cats, cows, horses, and pigs “Copy Cat” was the first cat cloned

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Problems Associated with Animal Cloning In most nuclear transplantation studies, only a small percentage of cloned embryos have developed normally to birth Many epigenetic changes, such as acetylation of histones or methylation of DNA, must be reversed in the nucleus from a donor animal in order for genes to be expressed or repressed appropriately for early stages of development

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Stem Cells of Animals A stem cell is a relatively unspecialized cell that can reproduce itself indefinitely and differentiate into specialized cells of one or more types Stem cells isolated from early embryos at the blastocyst stage are called embryonic stem cells The adult body also has stem cells, which replace nonreproducing specialized cells Embryonic stem cells are totipotent, able to differentiate into all cell types Adult stem cells are pluripotent, able to give rise to multiple but not all cell types

LE 21-9 Embryonic stem cellsAdult stem cells Pluripotent cells Totipotent cells Cultured stem cells Different culture conditions Different types of differentiated cells Liver cellsNerve cellsBlood cells

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Transcriptional Regulation of Gene Expression During Development Cell determination precedes differentiation and involves expression of genes for tissue-specific proteins Tissue-specific proteins enable differentiated cells to carry out their specific tasks

LE 21-10_1 Nucleus Embryonic precursor cell DNA OFF Master control gene myoDOther muscle-specific genes

LE 21-10_2 Nucleus Embryonic precursor cell DNA OFF Master control gene myoDOther muscle-specific genes mRNAOFF Determination Myoblast (determined) MyoD protein (transcription factor)

LE 21-10_3 Nucleus Embryonic precursor cell DNA OFF Master control gene myoDOther muscle-specific genes mRNAOFF Determination Myoblast (determined) MyoD protein (transcription factor) Differentiation Muscle cell (fully differentiated) mRNA MyoD mRNA Another transcription factor Myosin, other muscle proteins, and cell-cycle blocking proteins

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Cytoplasmic Determinants and Cell-Cell Signals in Cell Differentiation Maternal substances that influence early development are called cytoplasmic determinants These substances regulate expression of genes that affect the cell’s developmental fate Animation: Cell Signaling Animation: Cell Signaling