Biology / Unit 8 Bio 1755 short lesson, about 20 seconds
Only Germline Variation Is Heritable
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The idea
Only genetic variation in an organism's germline, cells producing sperm or eggs, can pass to offspring and be subject to selection.
In practice
A skin-cell mutation affects that cell's descendants but cannot reach the next generation, since it never enters the germline.
Where people slip
A somatic mutation spreading through one tissue, as in cancer, is not population evolution — it never reached the gene pool.
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