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Development •Homework #2 is due 10/18 •Bonus #1 is due 10/25 •Weekly quiz online each Thursday, due each Tuesday Developmental mutants of Drosophila melanogaster Fig 12.1 Vertebrate Development: from zygote to adult Besides adding cells, development can involve cell death. Development of a mouse paw: yellow areas show dying cells CB 21.19 Early embryo development Totipotent: ability to differentiate into any cell-type Totipotency is limited to early stages of animal development Why do cells lose totipotency? Why do cells lose totipotency? Mature, differentiated plant cells are totipotent Why do cells lose totipotency? •Gene expression can be controlled at many points between DNA and making the final proteins. •Changes in the various steps of gene expression control when and how much of a product are produced. Why change gene expression? •Different cells need different components •Responding to the environment •Replacement of damaged/worn-out parts DNA packaging fluctuates… genes being expressed are unpackaged, genes not needed are tightly packaged. Normally DNA is loosely packaged During mitosis DNA is tightly packaged as chromosomes and individually visible box 2.1 DNA packaging fluctuates… Some of the tight packaging of DNA is irreversible. Irreversible packaging of DNA partially explains the loss of totipotency. Stem cells still have totipotency Embryonic Stem Cells are totipotent Adult Stem Cells are pluripotent (only form some cell types) Developmental information can be encoded by both genetic and non-genetic information. Fig 12.2 What genetic mechanisms regulate/allow development? All humans are female for the first nine weeks of development All humans are female for the first nine weeks of development Down’s Syndrome is caused by an extra chromosome 21. Down’s Syndrome is caused by an extra chromosome 21. Too much information disrupts normal development. 4 whorls of a flower Flower parts: Complexity from a few simple genes Each whorl expresses a specific combination of three genes CB 21.20 Changing expression of A, B, or C genes changes organ identity CB 21.20 Hox genes regulate the identity of body parts Fig 12.4 embryo adult Expression of hox genes in the embryo give rise to different adult body parts. Fig 12.4+.6 The order of Hox genes parallels the order of body parts in which they are expressed Fig 12.10 • Drosophila and vertebrate Hox protein show striking similarities (500 million years since common ancestor) Fig 12.9 • Many hox proteins have common sequences (these are from Drosophila) Fig 12.8 helix-turn-helix: a common DNA-binding motif Fig 10.28+.29 Many developmental genes are transcription factors Tbl 12.1 these are from Drosophila Interaction of genes can set gradients in cells/organisms that signal how different regions should develop. Fig 12.18 Reporter gene: promoter coding region protein promoter reporter gene (luciferase, etc) easily visualized protein Fig 12.19 Interaction of genes can set gradients in cells/organisms that signal how different regions should develop. Fig 12.18 Mutants in Drosophila embryo segment development Fig 12.14 Gap genes affect formation of continuous blocks of segments Fig 12.14 Pair-rule genes regulate pairing of segments Fig 12.14 Segment-polarity genes regulate patterning of the segments. Fig 12.14 Hox genes regulate not segment patterns, but what each segment will become Fig 12.14 Why change gene expression? •Different cells need different components •Responding to the environment •Replacement of damaged/worn-out parts Development •Homework #2 is due 10/18 •Bonus #1 is due 10/25 •Weekly quiz online each Thursday, due each Tuesday