Loom

According to one view of Gallifreyan history, Looms were used by Time Lords to perpetuate their race in the wake of Pythia's Curse. Unable to procreate sexually, the Time Lords had to rely on the Rassilon-invented devices to "weave" new life from genetic material. (NA: Cat's Cradle: Time's Crucible, Lungbarrow)

According to Leela, each Family on Gallifrey had their own "Family Loom" which they used to create new members of their Family. She felt pity for Gallifreyans, because the Looms prevented "true children" from existing on their planet. Gallifreyans were born as "full-grown adults", although they were child-like at the time of their birth, and had to mature mentally like any young life-form. The genetic relationship between people originating from each Family Loom was lateral rather than direct, meaning that people from the same Loom were "cousins" of each other. (NA: Lungbarrow)

Looms also kept a tally of all the people they birthed, and could normally indicate how old each of its "offspring" was and how many regenerations each had gone though. Data from all the Family Looms on Gallifrey was sent to the Bureau of Loomographic Records, which served as a central repository of genetic information.

A Loom was given to each of the Houses of Gallifrey, and each House had a specified number of cousins which could exist in the Family at any given time. The House of Lungbarrow, for example was allotted 45 cousins. When a member of a Family died for the final time, the Loom would weave a new cousin into the Family. Cases did exist when an additional cousin was woven (such as the Doctor's cousin Owis) but were extremely rare, as such a thing was illegal. When he was only five years old, the Doctor boasted that he could remember existing in the Loom before he was actually born:

"I can remember waiting to be born...It was like being all strung out. All unravelled inside the Loom. I was spread really thin…I couldn’t think. Not put thoughts together. … But I knew where I was and what was happening. I couldn't wait to get out. And then I was born. My lungs nearly burst. The first rush of air was so cold...."''"

- NA: Lungbarrow

Behind the scenes

 * The idea that the Looms weave fully grown Gallifreyans appears to conflict with the depiction in the BBC Wales series of the Master looking like a child at 8 years old. It is possible that some Looms produce Gallifreyans as children (this would include the Loom of the Master's House, the House of Oakdown) and some as adults (apparently including the Loom of Andred's House, either Redlooms or Deeptree). In the classic series itself, as well, the Doctor mentioned his childhood, although he is portrayed as a older-looking child in Lungbarrow. Explicitly referring to when he was a "little boy" when telling a story in DW: The Time Monster.
 * The idea of Looms may contradict the Doctor's mentions of his parents, and the Master's mention of his father. It is possible there is some sort of adoption system on Gallifrey (meaning the Doctor might not be biologically half-human), or that people could give samples of their genetic material to a Loom to become "parents" (similar to the situation with the Tenth Doctor and Jenny), and this is backed up by The Infinity Doctors.