7
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Accepted
PCA plot shows big difference but not many differentially expressed genes are found
You only have 4 samples total. I think it would be difficult to not have the PCA show big differences between the groups with so few points.
On the other hand, for differential expression, it is hard ...
- 2,159
5
votes
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What does PCA mean on GWAS
From my memory of what a statistician told me, a PCA aims to determine independent linear combinations of variables (i.e. genotypes) that account for the most variation in the dataset. With 10 million ...
- 13.5k
5
votes
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3D PCA group labelling
You can easily color 3D pca plots in R based on the code given below:
...
5
votes
Accepted
How to interpret PCA output statistically and biologically?
All that plots like this are telling you is that there are some genes that contribute more to the variability seen between your various samples than others. In an ideal world these genes will also be ...
- 19.5k
4
votes
How are Principal Component analyses and Admixture analyses from a genetic alignment different?
Just to add to the great summary by Devon Ryan: admixture analysis tools are much more flexible than PCA (which is just a fixed mathematical operation), so they can be designed to incorporate LD ...
- 463
4
votes
Accepted
Should PCA be standardized for gene expression?
When the gene expression is scaled and centred you reduce the difference between genes.
Imagine you have one gene A that is highly expressed usually and has a standard deviation of 500 units ...
- 4,692
3
votes
Accepted
What is a sensible number of gene/observations to explain PCA variance?
The general goal of PCA in RNA-seq can be stated as, "I'd like a low-dimension representation of my data to allow easy assessment of the gross structure of my samples, specifically for assessing ...
- 19.5k
3
votes
Pre-filtering genes for Principal Component Analysis
You can filter out genes that do not show variation across samples, they would not differentiate samples anyway. For the specifics on how to do so, please see the ...
- 3,892
3
votes
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Interpreting this PCA plot for RNA-seq
Yes, you can safely concatenate the technical replicates. Odds are good that these are even the same libraries just sequenced twice, so even labeling them as replicates is a bit of a stretch. As an ...
- 19.5k
3
votes
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Understanding PCHeatmap outputs
The PCHeatmap function (renamed DimHeatmap in Seurat v3) can be used to help determine the number of principal components to use ...
- 674
3
votes
Accepted
PCA on genotype matrix with multiple alleles
You can make a 'dummy variable' for each allele. That means that you don't have info per SNP, but for SNPs with more alleles, the allele is present (1) or not (0).
- 3,571
3
votes
Accepted
How are Principal Component analyses and Admixture analyses from a genetic alignment different?
The fundamental difference lies mostly in the math.
An admixture analysis involves assuming that genotypes (or more likely, genotype likelihoods) in an unknown sample can be modeled with Hardy-...
- 19.5k
3
votes
Accepted
Using external list of PCs for clustering
There is a way to do this, and even better--there is documentation for how to do it! No surprise coming from the Satija Lab. In the vignette they perform multidimensional scaling, but the idea is the ...
- 1,139
2
votes
2
votes
PCA on genotype matrix with multiple alleles
I recommend the Hamming distance and doing a multidimensional scaling (a procedure similar to PCA but for distances), that way you don't create new variables for the same position.
The distance ...
- 4,692
2
votes
Hierarchial PCA Clustering with duplicated row names
Try to make your rownames unique first.
So if you have this matrix with duplicate rownames:
...
- 3,571
2
votes
Accepted
Perplexity is too large
I was using dudi_pca incorrectly. The supplied parameter to as.matrix() should have been ...
- 2,538
2
votes
What does PCA mean on GWAS
PCA = principle component analysis and a multivariate statistic, today it is trendily retermed "unsupervised learning" and here is likely being deployed for individuals within your data set. It works ...
M__♦
- 11.2k
2
votes
Accepted
Performing PCA for the samples and for the genes
First of all, I am not a statistician but have been performing RNA-seq analysis for a while, here is my take:
I think performing PCA on the samples makes sense in terms of mathematics. What I mean is ...
- 3,892
2
votes
PCA plot in R coloured by sample type
Can't say I've ever used autoplot, but this is fairly easy to achieve using "base" ggplot.
One thing autoplot does is put the axis on the same scale reflecting the percentage variation ...
- 301
2
votes
Test for differences between groups of samples
PCA does not do any testing and has no p-values. You may state that a separation of less than m units in PC > i is not ...
- 1,993
1
vote
Explanation for RNA-seq samples not clustering in PCA as expected
It's hard to say what is going on without looking at the plots. But it is a reasonable guess that samples are mislabelled and I think it is worth checking the experimental log carefully. It is also ...
- 857
1
vote
Biology behind PCA analysis based on SNP
First of all, PCA is a technique for dimension reduction. Basically, the goal is to compare tens of thousands of SNPs in Drosophila. Now if you only have 2 SNPs, you can plot them on a 2D scatter plot....
- 857
1
vote
Performing PCA for the samples and for the genes
It is quite possible to make a PCA plot with the samples. Follow this tutorial : https://hbctraining.github.io/DGE_workshop/lessons/03_DGE_QC_analysis.html
- 151
1
vote
Performing PCA for the samples and for the genes
If you use, say, R's prcomp, you can use my_pca_object$x to get PC coordinates for the samples, and my_pca_object$rotation to ...
- 1,882
1
vote
Accepted
data visualization RNAseq : scaling data for PCA and cluster dendogram
Scaling (or centering) makes the genes comparable: Putting the expression levels of genes in the same scale (i.e. between 0 and 1) sustains that all of your genes contribute equally to the PCA or ...
- 3,892
1
vote
the variation between treatments is less than the variation between replicates in RNA-seq data
If you got DEGs with statistically significant p-values after multiple testing following a valid pipeline, I'd believe that, even if looking at the first few PCs doesn't look promising.
- 1,882
1
vote
RNAseq biological replicates not clustering in PCA plots
You used Kallisto for alignment. I think Kallisto reports TPM values, are you using this value? DEseq2 uses count data, so I am not sure whether these two methods are compatible.
Also, I agree with ...
- 857
1
vote
RNAseq biological replicates not clustering in PCA plots
PC1 is 81% of the variance?
This PCA plot confirms that different tissues are different. You probably already knew that. I'd make more PCA plots that are tissue specific. That will be more ...
- 1,882
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