Developmental Genetics and Immunogenetics Benjamin A. Pierce GENETICS A Conceptual Approach FIFTH EDITION CHAPTER 22 Developmental Genetics and Immunogenetics © 2014 W. H. Freeman and Company

Alterations of key regulatory sequences often bring about major developmental changes.

Figure 22.1 Marine populations of threespine sticklebacks possess pelvic spines (a) but the spines are reduced or missing in sticklebacks from many freshwater lakes (b).

22.1 Development Takes Place Through Cell Determination Totipotent cell: the cell that has the potential to develop into any cell types Determination: a cell becomes committed to a particular cell fate Cloning experiments on plants Cloning experiments on animals

Figure 22.2 Many kinds of plants can be cloned from isolated single cells. Thus none of the original genetic material is lost in development.

Figure 22.3 In 1996, researchers at the Roslin Institute of Scotland successfully cloned a sheep named Dolly.

The Development of the Fruit Fly Egg-Polarity Genes 22.2 Pattern Formation in Drosophila Serves as a Model for the Genetic Control of Development The Development of the Fruit Fly Egg-Polarity Genes Determination of the dorsal-ventral axis Determination of the anterior-posterior axis Segmentation genes Homeotic genes in Drosophila Homeobox genes in other organisms Epigenetic changes in development

Figure 22.4 The fruit fly Drosophila melanogaster passes through three larval stages and a pupa before developing into an adult fly. The three major body parts of the adult are head, thorax, and abdomen.

Figure 22.5 Early development of a Drosophila embryo.

Figure 22.6 In an early Drosophila embryo, the major body axes are established, the number and orientation of the body segments are determined, and the identity of each individual segment is established. Different sets of genes control each of these three stages.

22.2 Pattern Formation in Drosophila Serves as a Model for the Genetic Control of Development Egg-polarity genes: Maternal origin: determination of anterior-posterior and dorsal-ventral axes of the embryo Morphogen: protein; its concentration gradient affects the developmental fate of the surrounding region.

22.2 Pattern Formation in Drosophila Serves as a Model for the Genetic Control of Development Determination of the dorsal-ventral axis Dorsal gene Determination of the anterior-posterior axis Bicoid gene, nanos gene, hunchback gene

Figure 22.7 Dorsal protein in the nuclei helps to determine the dorsal- ventral axis of the Drosophila embryo.

Figure 22.8 The anterior-posterior axis in a Drosophila embryo is determined by concentrations of Bicoid and Nanos proteins.

Concept Check 1 High concentration of which protein stimulates the development of anterior structure? Dorsal Toll Bicoid Nanos

Concept Check 1 High concentration of which protein stimulates the development of anterior structure? Dorsal Toll Bicoid Nanos

22.2 Pattern Formation in Drosophila Serves as a Model for the Genetic Control of Development Segmentation genes: control the differentiation of the embryo into individual segments Gap genes: broad region gap differentiation Hunchback Pair-rule genes: affect alternate segments Segment-polarity genes: development of individual segments

Figure 22.9 Segmentation genes control the differentiation of the Drosophila embryo into individual segments. The gap genes affect large sections of the embryo. The pair-rule genes affect alternate segments. The segment-polarity genes affect the polarity of segments.

22.2 Pattern Formation in Drosophila Serves as a Model for the Genetic Control of Development Homeotic Genes in Drosophilia: identity of segments Homeobox Genes in Other Organisms: genes encoding DNA binding proteins; these proteins usually play a regulatory rule. Hox genes: encode transcription factors that help determine the identity of body regions Epigenetic Changes in Development

Figure 22.10 The homeotic mutation Antennapedia substitutes legs for the antennae of a fruit fly. (a) Normal, wild-type antennae. (b) Antennapedia mutant.

Figure 22.11 Homeotic genes, which determine the identity of individual segments in Drosophila, are present in two complexes. The Antennapedia complex has five genes, and the bithorax complex has three genes.

Figure 22.11 Hox genes in mammals are similar to those found in Drosophila.

Figure 22.13 A cascade of gene regulation establishes the polarity and identity of individual segments of Drosophila. In development, successively smaller regions of the embryo are determined.

Concept Check 2 Mutations in homeotic genes often cause: the deletion of segments. the absence of structures. too many segments. structures to appear in the wrong places.

Concept Check 2 Mutations in homeotic genes often cause: the deletion of segments. the absence of structures. too many segments. structures to appear in the wrong places.

22.3 Genes Control the Development of Flowers in Plants Flower Anatomy Genetic Control of Flower Development

Figure 22.13 The flower produced by Arabidopsis thaliana has four sepals, four white petals, six stamens, and two carpels. [Darwin Dale/Photo Researchers.]

Figure 22.15 Analysis of homeotic mutants in Arabidopsis thaliana led to an understanding of the genes that determine floral structures in plants.

Figure 22.16 Expression of class A, B, and C genes varies among the structures of a flower.

22.4 Programmed Cell Death Is an Integral Part of Development Apoptosis Controlled, programmed cell death Necrosis: injured cells dying in an uncontrolled manner Caspases Regulation of apoptosis Apoptosis in development Apoptosis in disease

Figure 22.17 Programmed cell death by apoptosis is distinct from uncontrolled cell death through necrosis.

22.5 The Study of Development Reveals Patterns and Processes of Evolution Common genes in a developmental pathway Evolution through change in gene expression

Figure 22.18 Expression of the eyeless gene causes the development of an eye on the leg of a fruit fly. Genes similar to eyeless also control eye development in mice and humans.

Figure 22.19 Mexican tetras that live in caves have lost their eyes through a developmental change in gene expression.

22.6 The Development of Immunity Is Through Genetic Rearrangement Antigen: molecules that elicit an immune reaction Antibody: proteins that binds to antigens and mark them for destruction by phagocytic cells The Organization of the Immune System Humoral immunity: the production of antibodies by B cells Cellular immunity: depends on T cells Clonal Selection: primary response, memory cells, secondary response

Figure 22.20 Immune responses are classified as humoral immunity, in which antibodies are produced by B cells, and cellular immunity, which is produced by T cells.

Figure 22.21 An immune response to a specific antigen is produced through clonal selection.

22.6 The Development of Immunity Is Through Genetic Rearrangement Immunoglobulin Structure The Generation of Antibody Diversity Somatic recombination Major Histocompatibility Complex Genes Genes and Organs Transplants

Figure 22.22 Each immunoglobulin molecule consists of four polypeptide chains—two light chains and two heavy chains—that combine to form a Y- shaped structure.

Figure 22. 23 Antibody diversity is produced by somatic recombination Figure 22.23 Antibody diversity is produced by somatic recombination. Shown here is recombination among gene segments that encode the human kappa light chain.

Figure 22.24 A T-cell receptor is composed of two polypeptide chains, each having a variable and constant region. Most T-cell receptors are composed of alpha and beta polypeptide chains held together by disulfide bonds. One end of each chain traverses the cell membrane; the other end projects away from the cell and binds antigens.

Figure 22.25 T cells are activated by binding both to a foreign antigen and to a histocompatibility antigen on the surface of a self-cell.

Genes and Organ Transplants Organ transplant requires genetic match Immune rejection MHC antigens The greater the mismatch, the stronger the immune rejection Rejection partially inhibited by drugs ABO red blood cell antigens also important Figure 22.23 T cells are activated by binding both to a foreign antigen and to a histocompatibility antigen on the surface of a self-cell.