BIO 152 1st Edition Lecture 5Outline of Last LectureDisadvantages i. Diffusion II. How Genes Control Cell Fate Outline of Current LectureBasic Principles Morphogens Two Models for Control Hierarchical Segmentation Current Lecture**Clicker Question**Human glial cells were implanted into neonate mice. Would the opposite work (mice glial cells implanted into humans)?whether they could respond to the signal or not, they appear to be less “fit” than the hs glial cells you can’t tell that they would necessarily respond to the signal. Just because Mm cells can respond to the Hs signal doesn’t mean the opposite is true.Mice and humans shared a common ancestor around 90 million years ago• means that the gene codes for the protein for the cell/receptor has been basically the same for 90 MYBasic Principles of How Genes Control Development and Differentiation• morphogens = determine cell fatesubstance that governs the pattern of tissue development, including position, what to become, and whether to live or to die undifferentiated cells get a signal (morphogen, often acting as a transcription factor) —> tells cell to “turn on” certain genes —> transcription factor turns on other TF’s which start to modify the cell —> cell begins to specialize —> more regulatory genes turn on & proteins do their job —> end up with completely specialized cell**Clicker Question**Thinking back to the human glial cells implanted in the mice, which of the following related to the process of specialization is probably true?just because a receptor binds the signal doesn’t mean the process inside thecell (signaling cascade) will be identical the mouse “turn into a glial cell” signal must be similar enough to the human signal to bind to and activate the Hs receptor Two Models for Development Control1. HierarchicalSegmentation common evolutionary innovation in animals body is segmented into like repeating pieces — during development the organism controls what each of these segments will become in humans this is only seen clearly in the embryonic stage, but in other organisms it is clearer (like in arthropods) Dorsophilia (fruit fly) life cycle egg—> cell division —> larva —> fly at gastrolation how do genes control segmentation? anterior-posterior polarity is determined by maternally produced mRNA happening at the cellular blastoderm stage when egg is laid, female fly puts mRNA into the egg determines anterior and posterior end of the organism **Clicker Question**If mama fly doesn’t make b (bicoid) or c (nanos), the larva display shown phenotype — the bristles are distinctive for each segment. What part of the larva does nanos control?if the mother fly doesn’t make nanos, and the larva from the nanos mutant only shows the anterior end and not the posterior one, then the nanos would be responsible for the formation of the posterior end. maternal effect genes = mRNA expressed by the mother that has an effect on the embryo**Clicker Question**Why is the protein gradient bigger than the mRNA gradient when looking ata comparison between the two in the anterior end of embryonic cells?•many proteins could be translated from one mRNA — this means that there is an amplification affect causing there to be more protein than mRNA•different mRNA have different half-lives, and the half-life determines how longit can be used to make proteinDifferent Genes Control Segmentation in a Hierarchical PatternMaternal: tells you anterior and posterior gap genes : tells you broad sections (middle region, head region, etc.) pair rule genes: make the segments by turning on every other segment segment polarity genes: give each segment a back and a front hox genes: identification of the segments **these all happen in this particular order when the embryo is developing**knocking out a level of this hierarchy disrupts the formation of part of the body — almost all lethal to the embryohox genes = transcription factors that have particular DNA binding domains — for example, they might say that a section is T1, so that section must grow 1 set of wingsif you knock out that gene then the fly might end up with two pairs of wings instead hox genes have a conserved sequence that makes them identifiable they give characteristics : wings, legs, tendons, etc. —tells a segment what to become they occur on a single chromosome in 2 clusters — occur in the order that they are expressed in the embryo ex: the first ones tell you about the front of the fly, the last ones tell you about the back of the fly **Clicker Question**A fly has legs where it should have antennas, and it is a mutation affecting the Antp gene. This gene controls T1-T3 and makes legs. Is it knocked out (no expression) or expressed at the wrong time (ectopic expression)?ectopic expression—the organism still makes the legs, however it just 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.makes them inthe wrong