The correct answer is option 'D', Aam Aadmi Party (AAP).

The Janata Party was formed in 1977, following the defeat of the Congress party in the 1977 general elections. It was an amalgamation of various opposition parties and groups, including the Bharatiya Lok Dal, the Socialist Party, and the Congress (O). The Janata Party formed the government at the center with Morarji Desai as the Prime Minister.

However, due to ideological and personality clashes, the Janata Party's unity began to crumble, leading to the formation of various splinter groups and parties. Let's discuss the fate of the parties that emerged after the Janata Party's rule:

1. Bharatiya Janata Party (BJP):
The Bharatiya Janata Party (BJP) emerged as a separate entity from the Janata Party. It was formed in 1980 under the leadership of Atal Bihari Vajpayee and L.K. Advani. The BJP went on to become one of the major political parties in India and is currently the ruling party at the center.

2. Janata Dal:
The Janata Dal was formed in 1988 as a result of the merger of various political parties, including the Janata Party, the Lok Dal, and the Jan Morcha. It was led by V.P. Singh, who later became the Prime Minister of India. The Janata Dal had several factions and underwent multiple splits over the years, giving rise to parties such as Janata Dal (United), Janata Dal (Secular), and Rashtriya Janata Dal.

3. Samajwadi Party:
The Samajwadi Party was formed in 1992 by Mulayam Singh Yadav, who was a prominent leader within the Janata Dal. The party primarily focused on the interests of the backward castes and minorities and gained significant influence in the state of Uttar Pradesh. It continues to be a major political force in the state.

4. Aam Aadmi Party (AAP):
The Aam Aadmi Party (AAP) is a relatively new political party that emerged in 2012. It was formed by Arvind Kejriwal, along with several other activists and former members of the India Against Corruption movement. The AAP gained prominence for its anti-corruption stance and its focus on participatory governance. It formed the government in Delhi in 2013 and has since become a significant player in Indian politics.

In conclusion, out of the parties mentioned, the Aam Aadmi Party (AAP) is the one that did not emerge as a separate entity from the Janata Party. It was formed many years after the Janata Party's rule and has its own distinct identity and ideology.