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So there was a recent review article published in Neuron that examines the literature on this question. I'll paraphrase it and link it at the bottom:
First off some background, left-right asymmetries in the CNS used to be thought of as solely in humans. This was because of handiness but more importantly the discovery of language being mostly processed by the left cerebral hemisphere.
So in the 1970s it was discovered that some other animals, like rats and chicks, had functional brain asymmetries. To date, this has more generally been shown in worms, insects, and all sorts of vertebrates. Birds and fish have been shown to use one eye to pay attention to food while using the other eye to scan for predators while feeding. This seems to be a clear example of how functional brain asymmetries could interact with selective pressures.
Now, left-right asymmetry (think internal organs) begins early in embryonic development. During neurulation, when the neural tube forms, the leftmost mesoderm begins a genetic patterning process that leads to these left-right asymmetries. Scientists have done genetic studies on, most notably, zebrafish to better understand how this might affect CNS development.
Some important points...
1. primary ciliary dyskinesia is a genetic condition where half the people affected have a mirrored distribution of their internal organs (think liver on the left side) but they are mostly right handed.
2. tons of genome studies have found no single gene to correlate well with left handedness, a recent paper proposed that handedness might be determined by 40 genes interacting with the environment. Some of these papers implicate genes involved with schizophrenia or dyslexia.
3. covariation analysis with identical twins say that most of handedness must be determined through environmental interactions.
4. a recent paper has said that language lateralization and handedness have a complex relationship, with left handed people correlating with more VARIATION in the lateralization of language processing.
5. when babies lie on their stomach, they tend to turn to the hand that later becomes dominant.
Tl,Dr: its complicated, not determined by genes that do the general body plan. But if you watch how a baby sleeps you can generally predict which hand they will write with.
There's nothing here!