Genetic differences are due to variation in genes each inidividual possesses. Genetic variation arises due to mutation, meisos (nuclear division when a gamete is formed) and the fusion of gametes (when fertilisation occurs, and gametes fuse).
Enviromental influences e.g. a buttercup has a gene allowing it grow tall, but because it germinates in poor light, it will be short.
In most cases, variation is a result of environmental and genetic factors...
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