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UMass Amherst BIOLOGY 152 - Genes and Plant Physiology

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BIO 152 1st Edition Lecture 6Outline of Last LectureBasic Principles a. Morphogens Two Models for Control a. Hierarchical Segmentation Outline of Current LectureHox Genes 2R hypothesis Pax-6 Genes b. Combinatorial Floral Morphology ABC hypothesis Current LectureThese 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.*First exam is 2/11 at 7 pm*Two models for developmental control -Hierarchical-Combinatorial Hierarchical review **Clicker Question**Put the genes in proper hierarchical order for embryo developmentmaternal genes gap genes — tell us about major body portions pair rule genes — every other segment (would say that the first segment is 1, the third is 3, and so on) segment polarity genes — say that one side of segment 1 is the front part (anterior) and the other side is the back (posterior) hox genes — tells what specific body part belongs where Hox GenesTF’s that regulate gene expression in the embryo — determine much of howa body looks specify what each of the particular segments are going to become & what part of the thorax they arethey’re situated in the order that they’re going to be expressed in the organism **Clicker Question**Humans use similar genes to control embryo development but in vertebrates there are 4 separate clusters of hox genes (A-D). How could thisvertebrate lineage have happened?Answer: There were two genome duplication effects early in vertebrate history more genes may have been necessary as organisms become more complex, however the composition of the body did not come before the development of the genes organisms don’t make mutations in order to accomplish something Vertebrate Conservation of Hox = the 2R hypothesis2 rounds of duplication — genes were doubled once then those clusters were doubled again genes were the same but one cluster could mutate and develop new functions if you have 4 sets, the first one maintains its integrity but the others can now mutate to allow new tasks to be taken onthis explains what we see in the genome — it is only a hypothesis because it can’t be proved but it is difficult to refute each hox gene is a gene that turns on a transcription factor — they’re synchronized in the sense that different ones can handle development on different ends of the embryo Pax-6 Genenot a homeobox gene but does contain a similar sequence (protein sequence) acts as a transcription factor highly conserved — through evolution there has been little change in the sequence identical for mice and humans ex: when it is knocked out in mice it results in an eyeless mouse — works in the same way for fruit flies **Clicker Question**If you express mouse pax-6 ectopically (at wrong time and place) in the fruit fly,afterknocking out fly pax-6 you get a fly eye instead of an antenna. Why?• the fly cells can respond to the mouse pax-6 — because pax-6 is just a transcription factor that says “make an eye”• stem cells in the embryo are pluripotent — can become either eyes or antennae• at embryonic level the cells need to be able to become either an antenna or aneye (this is all happening when organism is in the embryonic stage)the cells have fly DNA so they make fly eyesCombinatorialless well conserved outside of plants flowers & leaves develop from top of the plant = apical meristem genes control what organs develop (leaves, flower, etc.) Floral Morphology• carpal = where egg cells get formedsepals = small leaf-like structures at the base stamen ultimately grows the pollen (“male” part)these all grow in “whorls” surrounding the central axis of the flower ABC Hypothesis for genetic control of flower formation3 types of genes (A,B,C) when C is expressed = carpal (female part) •B+C expressed = stamen (male part)•A+B expressed = petals•A represses C and vice versa**Clicker Question**What would the flower look like if you ectopically expressedB function genes in all the whorls?•two whorls of petals and 2 whorls of stamenA and C are still being expressed normally, but B is beingexpressed the whole time • B always happening, A happening in 2 whorls (A+B = petals), C happening in 2 whorls (B+C = stamen)**Clicker Question**What would the flower look like if you knocked out the A function genes?Whorls 1 & 4 would be carpals, 2 &3 would be stamen if A is knocked out then C takes its place — so instead of A alone producing sepals, it would be C alone producing carpals instead of A + B producing petals, it would be C + B producing stamen and it would be normal for the other two C


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