I just felt that I should post how Morning Musume was created!
Japanese producer Tsunku started the group in 1997 through a female rock vocalist audition for his band Sharam Q held on the Japanese TV show "Asayan". The winner of the audition was Heike Michiyo, later to become a soloist part of Hello! Project. Soon afterwards Tsunku decided to form a girl group consisting of five of the runnerups. They were issued a challenge to sell 50,000 copies of their demo single ?Ai no Tane? within 5 days. They managed the feat in four days in a very grass roots manner, and Tsunku kept on with his mission to create one of the most famous all-girl groups, giving them dance and vocal lessons. The group is particularly well-known for its shuffled line-up, with "graduations" occurring each year ("retiring" a girl from the group), then holding auditions to fill in open slots.
In the beginning of 1998 the girls were ready to start off with their first official single "Morning Coffee." The success of this single (hitting No. 6 on the Japanese pop charts) brought them 3 new members (Kei Yasuda, Mari Yaguchi, and Sayaka Ichii), for a total of 8. Their third single "Daite! HOLD ON ME" hit #1 on the charts. During this time, leader Yuko Nakazawa started her solo career--beginning with traditional japanese folk style called "enka" but eventually moving on to slower, mellow pop music.
In 1999, after several more releases, Asuka Fukuda left the group in order to focus on her studies. Also Tanpopo, the first subgroup, was formed with Kaori Iida, Aya Ishiguro, and Mari Yaguchi--touting slower, more mature songs.
Expectations for the third generation audition were to admit two new girls to the group, but ultimately, only one girl was added to the group, Maki Goto, the youngest member of the group at a mature-looking thirteen years. The success of the 7th single "LOVE Machine" with the addition of Goto dramatically increased the idol popularity of the group, while arguably making Goto the most popular member of Morning Musume.
This is furthered by placing Maki with Kei Yasuda and Sayaka Ichii to form subgroupPetitmoni (also known as Pucchi moni), which released their first single "Chokotto Love" three months after "LOVE machine" to great success.
In 2000, Aya Ishiguro left the group to marry Shinya, drummer of J-rock band LUNA SEA. The 7-member group made one more single ("Koi no Dance Site") before another generation joined. It consisted of (Rika Ishikawa, Hitomi Yoshizawa, Nozomi Tsuji, and Ai Kago), and gave the group a completely different feel by adding in the young 12-year-old duo of Tsuji and Kago.
After one single ("Happy Summer Wedding") in this 11-member formation, Sayaka Ichii graduated to pursue her own music career (she became vocalist in japanese group Cubic Cross and later married fellow group member Naoki Yoshizawa, no relation to Hitomi Yoshizawa).
With Ishiguro and Ichii gone, both Tanpopo and Petitmoni updated their membership. Hitomi Yoshizawa joined Petitmoni, and Ai Kago & Rika Ishikawa were added to Tanpopo. Meanwhile, Mari Yaguchi had started performing informally with Ai Kago and Nozomi Tsuji in concerts as Mini Moni, a group tailored towards younger audiences with members all being less than 150 centimeters tall (about 5 feet). Mika Todd of Coconuts Musume was later added into the group and Tsunku made them official. Their debut single, "Minimoni Jankenpyon!", was a #1 hit.
2000 also saw the creation of "summer shuffle units," in which all members of Tsunku's big idol family, Hello! Project, were shuffled around to form three one-time summer groups.
As an idol group, they were extremely successful, drawing comparisons to the popularity of former girl idol group SPEED. "Renai Revolution 21", "I Wish", and "The Peace" continued the trend of happy pop songs, becoming a staple hit for the group. Morning Musume also began their tradition of performing in musicals each year, breaking new ground as idols with their hit musical, "LOVE CENTURY."
Group leader Yuko Nakazawa graduated in April 2001 to concentrate more on her solo career, putting Kaori Iida and Kei Yasuda as Morning Musume's co-leaders. During this time, the popular Rika Ishikawa was "lent" out to the rather dormant group, Country Musume.
At the end of 2001, four new girls joined the group as the fifth generation: Ai Takahashi, Asami Konno, Makoto Ogawa, and Risa Niigaki, bringing the roster to 13 girls.
Late 2002 was marked by the graduation of Maki Goto and a mass re-shuffle of the sub-units. Tsunku removed Kaori Iida, Mari Yaguchi, and Ai Kago from Tanpopo, adding in Asami Konno, Risa Niigaki, and Ayumi Shibata (of Melon Kinebi) to join Rika Ishikawa. Tanpopo only released one single with this line-up before the group was put on a indefinite hiatus status. Makoto Ogawa and Ayaka Kimura (of Coconuts Musume) joined Hitomi Yoshizawa in Petitmoni to replace Kei Yasuda and Maki Goto, but the group did not even release a single, only performing in concerts. Their song was later released on the Hello! Project's compilation CD Petit Best 4. In Minimoni, Mari Yaguchi was replaced with Ai Takahashi and the new line-up went on to make several singles and a 2nd album until member Mika Todd graduated in May 2004, adding minimoni to the "indefinite hiatus" subgroups.
In the beginning of 2003, three new girls were added as the sixth generation: Eri Kamei, Sayumi Michishige, and Reina Tanaka. After a successful appearance on the New Year's music program "Utagassen Kouhaku" with several Morning Musume members dancing as backup, Tsunku also added in Miki Fujimoto, who was originally an up-and-coming solo singer under Hello! Project, as part of the sixth generation. Their debut concert was also Kei Yasuda's graduation concert, and Tsunku said that this one-time 16-member group is the largest Morning Musume will ever be.
Mari Yaguchi became Morning Musume's sub-leader (after Kei's graduation) and was also put in charge of training and assisting the up and coming group of Hello! Project Kids, eventually forming a group with 5 of them, known as ZYX.
Later in 2003, Morning Musume was split into two subgroups so that it can tour more cities (especially smaller cities that cannot support a 15-member troupe). Morning Musume Sakuragumi included Natsumi Abe, Mari Yaguchi, Hitomi Yoshizawa, Ai Kago, Ai Takahashi, Risa Niigaki, Asami Konno and Eri Kamei and Morning Musume Otomegumi had Kaori Iida, Rika Ishikawa, Nozomi Tsuji, Makoto Ogawa, Miki Fujimoto, Sayumi Michishige, and Reina Tanaka. Both groups made 2 singles so far and were reasonably successful.
In January 2004, Natsumi Abe (known as "the face of Morning Musume" to the general public) graduated to pursue a soloist career, followed by the graduation of 4th generation Nozomi Tsuji and Ai Kago in August to focus on "W (Double U)", their new duo group.
7th generation auditions (named "Lucky 7" to commemorate the 7th generation, 7th year of Morning Musume, and 7 auditioning locations across Japan) were held in various Japan cities in 2004, resulting in 6 finalists. However, on January 9th, 2005, Tsunku announced that no one in the Lucky 7 audition will be added onto Morning Musume, adding that he had set his expectations extra high this year in hopes of finding an "ace".
On January 30th, 2005 - then-leader and last 1st generation member Kaori Iida graduated to pursue a solo singer/artist career, with Mari Yaguchi taking on leadership role and Hitomi Yoshizawa as subleader. Also, Rika Ishikawa is scheduled to graduate in May 2005 and perform with another group (named "Biyuden", whose first single came out in September 2004)
In February 2005, Tsunku will start another audition for Morning Musume's 7th generation. He has noted that he is still intent on finding an "ace".
This information was taken from Wikipedia