Chromosome

Double-helix DNA was the "heart of the chromosome", as described by Todd. The Kinda wore necklaces embossed with a design akin to a double-helix. (TV: Kinda)

Female humans normally had XX chromosomes (PROSE: Girl Power!, Interference - Book One) while male humans normally had XY chromosomes. However, some individuals with XY chromosomes did not respond to male hormones and had a body that appeared female. Journalist Charles Peters was one such individual; he was raised as a girl but identified as a boy by the age of fifteen. (PROSE: Blue Box) Despite his male appearance, Jack Harkness' DNA and cell structure was more complex than an average human's; he lacked a strict dichotomy between male and female chromosomes. (PROSE: Exodus Code)

Instead of the more common pairs, Time Lords had 69 chromosomes arranged into 23 "homogeneous triads". (PROSE: Interference - Book Two)

While examining Dexeter's tissue sample, the Fourth Doctor said that he was "reduced to a tangle of stained chromosomes". (TV: Full Circle)

At the creation of the Daleks, Davros outlined chromosomal variations that were introduced into embryo Daleks. (TV: Genesis of the Daleks)

Ace observed that the Imperial and Renegade Daleks hated each other's chromosomes. (TV: Remembrance of the Daleks)

Gwen Cooper had the chromosome marked for synaesthesia. (PROSE: Exodus Code)

Spider germs were prokaryotic life with non-chromosomal DNA. (TV: Kill the Moon)

The Tenth Doctor created a DNA scanner that detected the chromosomal reading of fundamental DNA type 467-989 of the Daleks from Skaro. (TV: Daleks in Manhattan) When Dalek Sec worked to create human-Dalek hybrids, the Tenth Doctor said that chromosomal grafting was too erratic and that Sec would need to split the genome and force the sequence into the cortex. (Evolution of the Daleks)