Name:___________________________________ Section:_____7.012 Fall 2003 17.012 Problem Set 7Question 1A female geneticist has difficulty characterizing flies by their eye color because she herself is red-greencolorblind (an X-linked recessive phenotype). She has one sister (colorblind) and one brother (notcolorblind).a) Sketch a pedigree that includes the geneticist, her sister, her brother, and their parents; indicategenotypes (clearly define your genotype symbols).b) If 8% of males in a human population are red-green colorblind, what are the frequencies of the wild-type and colorblindness alleles?c) What % of females in this population should be red-green colorblind?d) What % of females in this population should be carriers for red-green colorblindness?Please print out this problem set and record your answers on the printed copy. Answers tothis problem set are to be turned in at the box outside by 4:10 Wednesday, November 5.Problem sets will not be accepted late. Solutions will be posted on the web November 6, 2003.MIT Biology Department7.012: Introductory Biology - Fall 2004Instructors: Professor Eric Lander, Professor Robert A. Weinberg, Dr. Claudette GardelName:___________________________________ Section:_____7.012 Fall 2003 2Question 2a) Clearly the intracellular and extracellular environments, along with ion permeability,influence the profile of an action potential. On the diagram below, draw what you think anaction potential would look in the following altered conditions. Label each action potentialwith the corresponding condition.i) The external Na+concentration is lowered.ii) The external K+ concentration is lowered.iii) Scorpion toxin (slows the inactivation of Na+ channels) is added.Rest potential0+40 mV-70 mV.5 ms∼∼Rest potential0+40 mV-70 mV.5 ms∼∼Rest potential0+40 mV-70 mV.5 ms∼∼Rest potential0+40 mV-70 mV.5 ms∼∼Rest potential0+40 mV-70 mV.5 ms∼∼Rest potential0+40 mV-70 mV.5 ms∼∼Rest potential0+40 mV-70 mV.5 ms∼∼Rest potential0+40 mV-70 mV.5 ms∼∼Rest potential0+40 mV-70 mV.5 ms∼∼∼∼4.4 ms∼∼4.4 ms∼∼4.4 ms∼∼4.4 msFigure by MIT OCW.Name:___________________________________ Section:_____7.012 Fall 2003 3Question 2, continuedb) Action potential wave fronts can vary even within the same neuron. You find suchvariation when you generated action potential graphs from recordings taken in frog motorneurons. One of the graphs represents data recorded from the myelinated axon of a neuron,while the other represents data recorded from the cell body of the same frog motor neuron.Unfortunately, you forgot to label the graphs “taken from axon” or “taken from cell body”.Given the two action potentials below, label them properly, and explain how you know yourlabels are correct.Explain:0 1 2 3 4 0 2 4 6 80 1 2 3 4 0 2 4 6 80 1 2 3 4 0 2 4 6 80 1 2 3 4 0 2 4 6 80 1 2 3 4 0 2 4 6 80 1 2 3 4 0 2 4 6 80 1 2 3 4 0 2 4 6 80 1 2 3 4 0 2 4 6 80 1 2 3 4 0 2 4 6 80 1 2 3 4 0 2 4 6 8Time (ms)Figure by MIT OCW.Name:___________________________________ Section:_____7.012 Fall 2003 4Question 3The sensory neurons synapse onto the interneurons and release excitatory neurotransmittersto continue the action potential through to the motor neurons.• At which of the remaining synapses would you expect an inhibitory neurotransmitter(such as GABA) to be released? Clearly label either on the diagram or write explicitlywhich synapses you refer to.• At which synapse would you expect an excitatory neurotransmitter (such asacetylcholine)? Clearly label either on the diagram or write explicitly which synapsesyou refer to.Image removed due to copyright reasons.Name:___________________________________ Section:_____7.012 Fall 2003 5Question 4You work in a mouse lab, studying a colony of mutant mice with a depressed phenotype: theyshow little interest in eating, don’t interact with other mice, and don’t play with toys that yougive them.You decide to examine the brains of some of these mice, and look at a region of the brainpreviously shown to be important for ‘good feelings’.You look at synapses in this region and find that the presynaptic axon terminals of cells in themutant brain are filled with vesicles. You compare the number of vesicles in your mutantmouse with the number in a normal mouse, and find that there are significantly more vesiclesin the mutant cell.a) What process is may be affected by this mutation?b) What neurotransmitter is likely used to transmit signals in the network of neurons you arestudying?c) Considering the neurotransmitter in (b), how does a mutation that affects the process in (a)explain the mutant mouse’s behavior?d) Could a drug that inhibited the reuptake of the neurotransmitter at the synaptic cleft relievethe mouse’s depressed symptoms? Why or why
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