Chapter 21: The Genetic Basis of Development From single cell to multicellular organisms: –Embryonic development involves cell division, morphogenesis, and cell differentiation –Researchers study development in model organisms (fruit flies, nematodes) to identify general priciples Differential gene expression: –Different types of cells in an organism have the same DNA –Different cell types make different proteins, usually as a result of transcriptional regulation –Transcriptional regulation is directed by maternal molecules in the cytoplasm and signals from other cells

Chapter 21: The Genetic Basis of Development: continued Genetic and Cellular Mechanisms of pattern formation –Genetic analysis of development in Drosophila reveals how genes control development –Gradients of maternal molecules in the early embryo control axis formation –A cascade of gene activations sets up the segmentation pattern in Drosophila –Homeotic genes direct the identity of body parts –Homeobox genes have been highly conserved in evolution –Neighboring cells instruct other cells to form particular structures: cell signaling and induction in the nematode –Plant development depends on cell signaling and transcriptional regulation

Pudgy Mouse

Stargazer

Chapter 21: The Genetic Basis of Development From single cell to multicellular organisms: –Embryonic development involves cell division, morphogenesis, and cell differentiation –Researchers study development in model organisms (fruit flies, nematodes) to identify general priciples Differential gene expression: –Different types of cells in an organism have the same DNA –Different cell types make different proteins, usually as a result of transcriptional regulation –Transcriptional regulation is directed by maternal molecules in the cytoplasm and signals from other cells

Chapter 21: The Genetic Basis of Development: continued Genetic and Cellular Mechanisms of pattern formation –Genetic analysis of development in Drosophila reveals how genes control development –Gradients of maternal molecules in the early embryo control axis formation –A cascade of gene activations sets up the segmentation pattern in Drosophila –Homeotic genes direct the identity of body parts –Homeobox genes have been highly conserved in evolution –Neighboring cells instruct other cells to form particular structures: cell signaling and induction in the nematode –Plant development depends on cell signaling and transcriptional regulation

Mendel and the Gene Idea Gregor Mendel’s Discoveries –Mendel brought and experimental and quantitative approach to genetics –By the law of segregation, the two alleles for a character a packed into separate gametes –By the law of independent assortment, each pair of alleles segregates into gametes independantly –Mendelian inheritance reflects rules of probability –Mendel discovered the particulate behavior of genes

Mendel and the Gene Idea: continued Extending Mendelian Genetics –The relationship between genotype and phenotype is rarely simple Mendelian Inheritance in Humans –Pedigree analysis reveals Mendelian patterns in human inheritance –Many human disorders follow Mendelian patterns of inheritance –Technology is providing new tools for genetic testing and counseling

Mendel and the Gene Idea Gregor Mendel’s Discoveries –Mendel brought and experimental and quantitative approach to genetics –By the law of segregation, the two alleles for a character a packed into separate gametes –By the law of independent assortment, each pair of alleles segregates into gametes independantly –Mendelian inheritance reflects rules of probability –Mendel discovered the particulate behavior of genes

Mendel and the Gene Idea: continued Extending Mendelian Genetics –The relationship between genotype and phenotype is rarely simple Mendelian Inheritance in Humans –Pedigree analysis reveals Mendelian patterns in human inheritance –Many human disorders follow Mendelian patterns of inheritance –Technology is providing new tools for genetic testing and counseling

The Chromosomal Basis of Inheritance Relating Mendelism to Chromosomes –Mendelian inheritance has its physical basis in the behavior of chromosomes during sexual life cycles –Thomas Hunt Morgan traced a gene to a specific chromosome on fruit flies –Linked genes tend to be inherited together because they are located on the same chromosome –Independent assortment of chromosomes and crossing over produce genetic recombinants –Geneticists can use recombination data to map a chromosome’s genetic loci

The Chromosomal Basis of Inheritance: continued Sex Chromosomes –The chromosomal basis of sex varies with the organism –Sex-linked genes have unique patterns of inheritance Errors and Exceptions to Chromosomal Inheritance –Alterations of chromosome number or structure cause some genetic disorders –The phenotypic effects of some genes depend on whether they were inherited from the mother or father –Extranuclear genes exhibit a non-Mendelian pattern of inheritance

Calico Cat

Viscacha Rat

Cytoplasmic Inheritance

Traslocation

The Chromosomal Basis of Inheritance Relating Mendelism to Chromosomes –Mendelian inheritance has its physical basis in the behavior of chromosomes during sexual life cycles –Thomas Hunt Morgan traced a gene to a specific chromosome on fruit flies –Linked genes tend to be inherited together because they are located on the same chromosome –Independent assortment of chromosomes and crossing over produce genetic recombinants –Geneticists can use recombination data to map a chromosome’s genetic loci

The Chromosomal Basis of Inheritance: continued Sex Chromosomes –The chromosomal basis of sex varies with the organism –Sex-linked genes have unique patterns of inheritance Errors and Exceptions to Chromosomal Inheritance –Alterations of chromosome number or structure cause some genetic disorders –The phenotypic effects of some genes depend on whether they were inherited from the mother or father –Extranuclear genes exhibit a non-Mendelian pattern of inheritance