Assignment 1: Chromosome Structures


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## Assignment 1: Chromosome Structures

### Assignment Overview

In this assignment you will profile the overall structure of the genomes of several important species and then study human chromosome 22 in more detail.
As a reminder, any questions about the assignment should be posted to [Piazza](

### Question 1: Chromosome structures

Download the chomosome size files for the following genomes (Note these have been preprocessed to only include main chromosomes):

1. [Arabidopsis thaliana (TAIR10)]( – An important plant model species [[info]](
2. [Tomato (Solanum lycopersicum v4.00)]( – One of the most important food crops [[info]](
3. [E. coli (Escherichia coli K12)]( – One of the most commonly studied bacteria [[info]](
4. [Fruit Fly (Drosophila melanogaster, dm6)]( – One of the most important model species for genetics [[info]](
5. [Human (hg38)]( – us 🙂 [[info]](
6. [Wheat (Triticum aestivum, IWGSC)]( – The food crop which takes up the largest land area [[info]](
7. [Worm (Caenorhabditis elegans, ce10)]( – One of the most important animal model species [[info]](
8. [Yeast (Saccharomyces cerevisiae, sacCer3)]( – an important eukaryotic model species, also good for bread and beer [[info]](

Using these files, make a table with the following information per species:

– Question 1.1. Total genome size
– Question 1.2. Number of chromosomes
– Question 1.3. Largest chromosome size and name
– Question 1.4. Smallest chromosome size and name
– Question 1.5. Mean chromosome length

### Question 2: Sequence content

Download the human chromosome 22 from here: [](

– Question 2.1. How many As, Cs, Gs, Ts and Ns are found in the entire chromosome?
– Question 2.2. What fraction of the 100bp non-overlapping windows/bins across chromosome 22 contain at least one N?
– Question 2.3. Make a scatterplot of the %GC of 100bp non-overlapping windows across the chromosome: x-axis = chromosome location, y-axis = (#G + #C) / 100. Only include windows that do not contain any Ns.
– Question 2.4. Make a histogram of the number of bins of a given %GC: x-axis = %GC, y-axis = # bins with this %GC. You should use the same 100bp windows/bins as Q2.3 (i.e. windows that do not contain any Ns).
– Question 2.5. Recall that Illumina sequencing performs poorly when the %GC is <= 30% or >= 65%. Based on what you saw in Q2.3 and 2.4, what fraction of those bins (that do not contain any Ns) do we expect to sequence poorly?
– Question 2.6. Assuming the rest of the human genome has the same sequence composition as chromosome 22, how many bases of the human genome do we expect to sequence poorly? Hint: extrapolate the results from 2.5 to the size of the whole genome computed in 1.1.

### Hints

– Many of the questions can be addressed with standard command line [tools]( such as grep, wc, awk, sort, fold, etc
– You may wish to try out [datamash](
– You may find [samtools]( and especially `samtools faidx` helpful for indexing the fasta files
– Plotting can be done in any language; R or Python are recommended; Excel is okay but ugly 😛
– Mac and Linux can use the builtin terminal
– If you are using Windows, you may want to install [Ubuntu for Windows](
– The final PDF can be made in any system: Markdown, Word, Google Docs, LaTeX, HTML
– Be sure to clearly mark each question and subquestion

### Packaging

The solutions to the above questions should be submitted as a single PDF document that includes your name, email address, and
all relevant figures (as needed). Make sure to clearly label each of the subproblems and give the exact commands and/or code snippets you used for
solving the question. You do not need to show code for plotting. Submit your solutions by uploading the PDF to [GradeScope](, and remember to select where in your submission each question/subquestion is. The Entry Code is: 86KZZP.

If you submit after this time, you will start to use up your late days. Remember, you are only allowed 96 hours (4 days) for the entire semester!



PlaceholderAssignment 1: Chromosome Structures
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