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Genes and Development. Development of an organism Organisms contain many types of cells specialized both structurally and metabolically All descend from a single zygote Development is all changes that occur in life Cell determination Groups of cells become committed
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Development of an organism • Organisms contain many types of cells specialized both structurally and metabolically • All descend from a single zygote • Development is all changes that occur in life • Cell determination • Groups of cells become committed • Leads to cell differentiation • Differences among cell types due to differential gene expression
Nuclear equivalence • Nuclei of all differentiated cells are genetically identical • Different cells express different subsets of genes • Somatic cells • Germ line cells • Totipotency • Capability of cells to direct development of entire organism
Mouse models to study disease • Ethically researchers often cannot use humans as test subjects • Animal model is used instead • An example is cystic fibrosis, a genetic disease • Gene targeting is used to produce mice homozygous or heterozygous for cystic fibrosis
First cloned mammal • 1997 • Cloned sheep “Dolly” was born in Scotland • Genetic material derived from • Cultured adult sheep’s mammary gland cell • Fused with enucleated sheep’s egg • Cultured in vitro and transferred to host mother
Stem cells • Undifferentiated cells • Can produce differentiated descendants • Also retain ability to reproduce themselves • Totipotent stem cells • Give rise to all cell types • Pluripotent stem cells • More specialized
Exceptions to nuclear equivalence • Genomic rearrangements • Physical changes in gene structure • Gene amplification • More copies of certain genes for transcription
Choice of organisms for research in developmental genetics • Fruit fly, Drosophila melanogaster • Abundance of mutant alleles and ease of mapping new mutations on the chromosomes • Roundworm, Caenorhabditiselegans • Lineage of every somatic cell is known • Laboratory mouse, Mus musculus • Used in studies of mammalian development
Maternal effect genes • Genes that organize structure of egg cells • Genes in maternal tissues transcribed to produce mRNA molecules that are transported in egg • Analysis of mutant Drosophila revealed that these genes involved in polarity of embryo
Classes of genes involved in pattern formation of embryonic segments in Drosophila
Segmentation genes • Genes that generate a repeating pattern of body segments within embryo • Gap genes • Pair-rule genes • Segment polarity genes • Homeotic genes
Hox gene clusters
Induction and apoptosis • Induction in C. elegans • Developmental interactions with neighboring cells • Anchor cell induces surface cells to form vulva • Apoptosis in humans • During development, hand forms a webbed structure • Fingers become individualized when cells between them die
Mouse model for mammalian development • Transgenic mice studied • Early development of mice and other mammals similar • Almost all research in stages leading to implantation • Chimera • Organism containing two or more kinds of genetically dissimilar cells from two zygotes
Cancer and cell development • Cancer-causing oncogenes • Proto-oncogenes • Code for various growth factors or growth factor receptors • Respond to stimulation by growth factors • Cell may misinterpret signal and grow and divide inappropriately • Tumor suppressor gene mutation