Sex-biased chromatin and regulatory cross-talk between sex chromosomes, autosomes, and mitochondria

Table 1 Sex chromosome dosage and phenotypes in humans and D. melanogaster

Genotype	Human gonadal sex	Human phenotype	Fly gonadal sex	Fly phenotype
XO	Female	Turner female^a	Male	Sterile male
XX	Female	Female	Female	Female
XY	Male	Male	Male	Male
XXY	Male	Klinefelter male^b	Female	Healthy female
XYY	Male	Slightly atypical male^c	Male	Lesser characterized male
XXX	Female	Slightly atypical female^d	Female	Metafemale^e

‘Male’ and ‘female’ designations are based on gonadal sex. ^aXO (Turner) females have female external genitals but often have non-functioning ovaries, lack a menstrual cycle, and are sterile. Prevalence is estimated to be 1 per 2,000 live-born females[68]. ^bXXY (Klinefelter) males have male genitals but are often sterile and hypogonadic. They may display a range of female secondary characteristics, including enlarged breasts and small or undescended testes. Prevalence is estimated to be 1 per 658 live-born males[69]. ^cPrevalence of XYY males is estimated to be 1 in 1,000, but approximately 85% are never diagnosed. The phenotype commonly includes tall stature, macroenchephaly, macroorchidism, decreased muscle tone, and an increase in autistic spectrum disorder. Some may be at risk of reduced fertility[70]. ^dTriple X syndrome in females has a variable phenotype, and XXX females will often not display any abnormalities. The prevalence is about 1 per 1,000 female births[71]. ^eMetafemale Drosophila are often sterile and can display narrowed abdomens, wing abnormalities, irregular eye facets, and/or malformed legs. The observed frequency in adults is less that 1%, and viability post-eclosion is limited[72–75].

ISSN: 2042-6410