BIOL 1411 1st Edition Lecture 27 Outline of Last Lecture I Eukaryotic Gene Expression Outline of Current Lecture I Developmental Genetics Mutations Lecture Developmental Genetics Pattern formation the process that results in the spatial organization of tissues o Linked with morphogenesis o Programmed cell death apoptosis is also important Many cells and structures form and then disappear during development In developing human embryos connective tissue links the fingers and toes Later the cells between the digits die Morphogen gradients provide spatial information for pattern formation o Fate of a cell is often determined by where the cell is o Positional information come in the form a type of inducer a morphogen which diffuses from one group of cells to another setting up a concentration gradient Shh sonic hedge hog a morphogen Pattern formation in drosophila melanogaster o the adult fruit fly drosophila melanogaster has a segmented body head thorax and abdomen each made of several segments established in the embryo Segment identity in drosophila o Specification of body regions begins already when a female drosophila makes her eggs maternal effect genes o A series of embryonic genes are turned on and define the position of each cell in a segment relative to these axes segmentation genes o The hox genes control the ultimate identity of each body part antenna eye leg wing Genes in each stop code for transcription factors that control synthesis of later acting transcription factors a transcriptional cascade Segment identity in drosophila o The maternal effect genes regulate expression of segmentation gene which define segment number and orientation of each segment These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute o Three classes of genes act in sequence Gap genes organize broad areas Pair rule genes divide embryo into units of two segments each Segment polarity genes determine boundaries and anterior posterior organization in individual segments o Hox Genes Are expressed in different combinations along the length of the embryo They determine the morphology of each segment Are in two clusters ordered the same as their spatial expression in the embryo Clues to hox gene function came from homeotic mutants mutants with mis regulation of gene expression Hox genes are present in all animals including humans All hox genes encode highly similar DNA binding proteins Mutations o Mutations occur in two types Somatic mutations occur in somatic cells passed on by mitosis but not to sexually produced offspring Germ line mutations occur in germ line cells the cells that give rise to gametes A gamete passes a mutation on at fertilization A genetic mutation is a change in the nucleotide sequence of DNA that is transmitted to the next generation o Relationships between mutations and gene function Silent mutations do not change polypeptide sequence thus do not affect protein function Loss of function mutations affect protein function and may lead to structural proteins or enzymes that no longer work almost always recessive Gain of function mutations lead to a protein with altered function Conditional mutations cause phenotypes under restrictive conditions but are not detectable le under permissive conditions o Classification of mutations at the level of DNA sequence Point mutation results from the gain loss or substitution of a single base pair of DNA Small indels insertions or deletions of a few to hundreds of base pairs of DNA Chromosomal mutations are more extensive may change the position of genes or cause multiple genes in a DNA segment to be duplicated or lost
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