From The TARDIS Wiki.

Jenny was the artificially-created "daughter" of the Doctor created from his genes.

Biography

A short war waged on the planet Messaline between Humans and Hath. The Humans and Hath used progenation machines to instantly create mentally programmed young adults from DNA of a single parent. When the Doctor (with Donna and Martha) arrived on Messaline, he had Jenny made from him against his will from a skin sample just prior to an ambush by Hath.

The then-nameless Jenny pushed a button which triggered an explosion, causing the collapse of the tunnel that cut the group off from the Hath and from Martha. Shortly after, Jenny, was named by the Doctor's companion Donna Noble from the Doctor's original description of her as a 'generated anomaly'.

Jenny's commander, Cobb, had Jenny locked up with the Doctor and Donna. While in this cell, Donna proved to the Doctor that Jenny was indeed his daughter; she listened to Jenny's heartbeat and found that, like the Doctor, she had two hearts. Jenny helped the others by kissing Cline and then taking his pistol. The Doctor found his daughter very capable though inclined towards violence, though convinced her not to kill Cobb when she had the chance.

As the three of them made their way towards the Source, which Cobb and the Hath both sought, Jenny spoke with the Doctor about the possibility of traveling with him, and he told her that he would never leave her. The Doctor told the respective parties to end the war, whereupon General Cobb aimed his gun and shot at him. Jenny here showed her compassion by standing in the way of the bullet. She was shot through one of her hearts, and died, but did not regenerate.

While laying in state, however, Jenny returned to life, stole a shuttlecraft, and left Messaline, determined to save other worlds and to do "an awful lot of running" like her father. (DW: The Doctor's Daughter)

Davros tried to manipulate the Doctor when he moved the Earth to the Medusa Cascade by asking the Doctor how many people have died in his name. Jenny is one of the people he thinks of. The Doctor is unaware of Jenny's revival.

Personality

Jenny showed a lot of the brilliance, lust for life and determination typical of her father. Though programming had made her military-minded and goal-oriented, she soon adopted the Doctor's values and principles, though she could also challenge him.

Inherited characteristics

Like her father, Jenny has two hearts. She also had reflexes, precision timing and acrobatic ability far beyond that of almost any Human. After her death, she shortly returned to life, expelling a "breath" of pure energy, though, unlike other Time Lords undergoing regeneration, she did not change physically.

This could be speculated to be either an equivalent of a Time Lord's post-regenerative healing ability,an effect of dying while in proximity of the Source, or possibly that her "Birth" was counted as a regeneration. She could also have had an excess of energy like recently post-regenerative Time Lords as she was only recently 'born'. The 'breath' that she expelled appeared very similar to the gas in the Source, suggesting that the terraforming device aided her in returning to life and that she can't truly regenerate. Another theory is that she did what the Doctor did in the stolen earth and threw the energy at the nearest object with her genetic code DW: Journey's End. However, this is unlikely as Jenny was unlikely aware she had this power. Alternatively, it could have been a by-product of the progenation machine; as it was not designed to replicate beings as complex as Time Lords, it could be that it just did the best it could to copy the regeneration process. Thus, she can heal herself to an impressive extent, but the Doctor's genetic code was too complicated to replicate completely. It could also be that she is not a full Time Lord, being created from the progenation machine; thus, she is not capable of full regeneration, but merely of healing herself. Or maybe she's not old enough to regenerate yet.

Other information

The presence of Jenny drew the TARDIS to Messaline, paradoxically, before her creation, so that she, in effect caused herself to exist. (DW: The Doctor's Daughter)

As the Doctor is Jenny's father many of her relatives are unknown. She is the Doctor's youngest child as he states that he had fathered children and had a family before, making Jenny their sister on some level (or more accurately their half-sister as, assuming the Doctor's other children were born naturally, they would have the same father as Jenny but a different mother, since Jenny did not actually have a mother). (DW: The Empty Child, DW: Fear Her, DW: The Doctor's Daughter) Susan Foreman, the Doctor's granddaughter who travelled with him during his first incarnation and the only other relative other than Jenny to appear on screen, is technically Jenny's niece. (DW: An Unearthly Child, DW: The Empty Child)

Behind the Scenes

Jenny was played by Georgia Moffett, the daughter of Peter Davison, alias the Fifth Doctor.

It was Steven Moffat who suggested that Jenny be brought back to life at the end of the episode. There are rumours that Moffat has expressed interest in Jenny either returning to Doctor Who or having her own spin-off series. Georgia Moffett has also expressed interest in the character returning.

There has been lots of talk of who will be the new companion to the Doctor in series five, many people are wanting Jenny to fill the role. The Sun newspaper have published that she will be in one of the 2009 specials.