Sex differences in gene expression
We then quantified how sex was associated with chest skin gene
expression while including sample collection year in the model (year was
significantly associated with both the first and second principal
component of gene expression; PC1: year \(\beta\)=0.39, P =0.02;
PC2: year \(\beta\)=-0.22, P =0.003, Table S1, Fig. S2 ).
Males and females differed along the first principal component of gene
expression while including year as a predictor variable (PC1: sex\(\beta\)=-0.39, P =0.01, Fig. S3 ; PC2: sex\(\beta\)=-0.13, P =0.049). The results of the principal component
analysis did not change when we removed genes located on sex chromosomes
and analyzed only those found on autosomes (Fig. S4 ).
At the level of the individual genes, we found that 10.5% of the 10,212
detectably expressed genes exhibited significant differential expression
across males and females (n genes=1,068, FDR<20%), in
a model controlling for the effects of RQN, RNA concentration, RNA
extraction date, and year of sample collection. Of the 1,068
differentially expressed genes, 201 genes were female-biased and 867
genes were male-biased. The average standardized sex-bias gene
expression level for each individual illustrates that subadult males
exhibited an intermediate gene expression pattern that differed from
adult males (\(\beta\)=-0.66, P =0.003) and adult females
(\(\beta\)=0.45, P =0.04; Fig. 3B). The sample size for
subadult females (n =2) was too small to draw conclusions about
sex-bias gene expression trends in this age category.