A silly question today- if you were to add together all of the X chromosomes of all of the people in the world, what would their total mass be? To answer this, we are going to have to estimate the mass of an X chromosome, examine how many cells are in a human body, and just how many people there are in the world...

Sources for this episode:

• Bhartiya, A., Batey, D., Cipiccia, S., Shi, X., Rau, C., Botchway, S., Yusuf, M. and Robinson, I. K. (2021), X-ray Phytography Imaging of Human Chromosomes after Low-Dose Irradiation. Chromosome Research 29: 107-126.
• Ross, M. T., et al. (2005), The DNA sequence of the human X chromosome. Nature 434: 325-337.
• Sender, R., Fuchs, S. and Milo, R. (2016), Revised Estimates for the Number of Human and Bacteria Cells in the Body. PLoS Biology 14(8): e1002533.
• Tartaglia, N., Cordeiro, L., Howell, S., Wilson, R. and Janusz, J. (2010), The Spectrum of the Behavioural Phenotype in Boys and Adolescents 47,XXY (Klinefelter Syndrome). Pediatric Endocrinology Reviews 8(1): 151-159.
• Author unknown, Bionumbers (date unknown), Mass of X and Y chromosomes (online) (Accessed 14/12/2025).
• Author unknown, Worldometer, (date unknown), World Population Clock (online) (Accessed 14/12/2025).
• Author unknown, UNICEF (date unknown), How many children are there in the world? (online) (Accessed 14/12/2025).