.. Yet all species are uniqueOrganisms sometimes use disparate strategies to accomplish thesame developmental goal.Removal of one cell from the two-cell embryo of C.elegans will affectthedevelopmentof theembryo.Removal of a cell from a 6-10-cell human embrvo has no effect on thedevelopmentoftheembryo.WormHuman20-11
20-11 Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display . Yet all species are unique Yet all species are unique Organisms sometimes use disparate Organisms sometimes use disparate strategies to accomplish the strategies to accomplish the same developmental goal. same developmental goal. Removal of one cell from the two Removal of one cell from the two-cell embryo of cell embryo of C. elegans elegans will affect will affect the development of the embryo. the development of the embryo. Removal of a cell from a 6-10-cell human embryo has no effect on the development of the embryo. Worm Human
18.2 Using mutations to dissect developmentLoss-of-function mutationsGain-of-function mutationsBBCNormal functionLossof functionGain of function20-12
20-12 Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display 18.2 Using mutations to dissect development 18.2 Using mutations to dissect development Loss-of-function mutations function mutations Gain-of-function mutations function mutations A B C Normal function A C Loss of function A B C Gain of function B
Loss-of-function mutations reveal genes requiredfornormaldevelopmentNull mutations2.Hypomorphicmutations3.Conditional mutations4Dominant-negative mutationsLoss of function20-13
20-13 Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display 1. Null mutations Null mutations 2. Hypomorphic Hypomorphic mutations mutations 3. Conditional mutations Conditional mutations 4. Dominant Dominant-negative mutations negative mutations Loss-of-function mutations reveal genes required for normal development A C Loss of function B
Nullmutations（无效突变）Completelylacks function ofageneUseful for inferring the function of wild-type gene20-14
20-14 Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display 1. Null mutations ( Null mutations (无效突变) Completely lacks function of a gene Completely lacks function of a gene Useful for inferring the function of wild Useful for inferring the function of wild-type gene type gene
Constructing animals bearing null mutationsRecombinantdrugvectorcarryingdruggeneReplacethegene with awithindisruptedgeneAGeneAselective marker gene,Transformationleaving the upstream anddownstream sequenceNucleusdrugintact.KXTransform the cassetteGeneAinto cells.SelectfordrugRAphenotypeSelect the correcttransformantsDisruptedgeneinchromosomedrugAGene replacement(double crossing-over)20-15
20-15 Copyright © The McGraw-Hill Companies, Inc. Permission required to reproduce or display Constructing animals bearing null mutations Constructing animals bearing null mutations Replace the gene with a selective marker gene, leaving the upstream and downstream sequence intact. Transform the cassette into cells. Select the correct transformants. Gene replacement (double crossing-over)