A scientist is studying two types of worms. Worm X has DNA identical to its parent. Worm Y has a combination of DNA from two parents. The scientist determines that one of the worms has a survival advantage over the other worm.

Worm Y has DNA from two parents, so it reproduces sexually. Sexual reproduction combines genetic material from two parents and creates genetic variation among offspring. That variation can give some worms a survival advantage. Worm X’s DNA is identical to its parent’s, so it does not gain variation through asexual reproduction.

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