Sex and gender (SG) differences in the human brain are of interest to society and science as numerous processes are impacted by them, including brain development, behavior, and diseases. I will first provide a quick overview of the sex and gender differences in human brain and then further highlight two published works to systematically identify and characterize SG-biased genes by collecting publicly available single-cell data from the in-utero to elderly age in healthy, Alzheimer’s disease and multiple sclerosis sample. Sex and gender differences in the transcriptome were present through- out the lifespan and across all cell types. Although there was limited overlap among SG-biased genes across different age and disease groups, we observed significant functional overlap. Female-biased genes are consistently enriched for brain-related processes, while male-biased genes are enriched for metabolic path- ways. Additionally, mitochondrial genes showed a consistent female bias across cell types. We also found that androgen response elements (not estrogen) were significantly enriched in both male- and female-biased genes, and thymosin hormone targets being consistently enriched only in male-biased genes. The significant enrichment of androgen (not estrogen) response elements in both male- and female-biased genes suggests that androgens are important regulators likely establishing these SG differences in both males and females.