1. Draw a diagram of how chromosomes behave during meiosis in the “cells” below. This diploid organism has two chromosomes. Chromosome 1 is a long chromosome. The short chromosome is 2. Homologs inherited from the male parent are thin lines, while the ones from the female are thick. Draw chromosomes in the cells for each labeled stage.
2) Gregor Mendel defined two fundamental laws of transmission genetics in the late 1800s. These laws have been used to establish chromosome theory as scientists examined visible chromosomes in meiotic cells. What are Mendel’s two laws?
3) Indicate in your diagram of meiosis on the first page how Mendel’s laws are consistent with what we know about meiosis. In other words, indicate the reason for Mendel’s laws in the events of meiosis
4) How many different nucleotides can be found in an mRNA molecule? What are the names of the nucleotides?
5) How many different amino acids are coded for in an mRNA?
6) Give the name of four amino acids, and list all of the codons that code for each one of these four amino acids.
7) Suppose that life is discovered elsewhere in our solar system. When translation is studied by xenobiologists, it is found that the amino acids coded for by the extraterrestrial mRNA re the exact same amino acids as those coded for by earthly mRNA. Surprisingly, the number of nucleotides that are in alien cells does differ from what is observed on our planet.
a) Cells from the moon of Saturn have only two kinds of nucleotides. Does this have implications for the process of translation? What would be the minimum size for a codon? Explain the reasoning for your answer.
b) Cells from Mars have only three types of nucleotides in their mRNA? Again, what would be the minimum size for a codon? Explain your reasoning.
c) Cells from a moon around Jupiter have five different nucleotides in their mRNA. What would be the minimum size for a codon? Explain your reasoning.
7) Auxotrophic mutations have been extremely useful to study a number of processes in Escherichia coli and other bacteria.
a) Briefly define the term “auxotrophic.”
b) Suppose you were given two unlabeled tubes, one that contains a tryptophan auxotroph and the other that contains an aspartate auxotroph. Design an experiment to determine which auxotroph is found in each tube. Draw it, and explain the experiment.
8) You join a lab studying the fungus Neurospora crassa, . Your mentor has discovered a strain that is auxotrophic for alanine (mutant allele a) and is crossed to a strain that is auxotrophic for cysteine (mutant allele c). Linear asci were isolated, and they were classified in the following groups. A note on notation: where it says “a +”, this designates a chromosome carrying the mutant allele “a” and a wild type allele of “c” (designated as“+”).
a) What is the linkage relationship of these two genes to their centromere(s) and to each other. Specify the distances in map units.
If 1000 randomly selected ascospores from the same cross were plated on a plate of minimal medium, how many would be expected to grow into colonies? Explain your reasoning.
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