actually, i can think of two groups that are clearly under-represented.

1) women. under 30% of the parliament is female, who make up a bit more than 50% of the population. that greatly exceeds any concept of error.

2) queer people only make up about 1% of the parliament, but make up roughly 10% of the population - a number greater than the number of blacks, indo-canadians and muslims, combined. this would be the single biggest under-represented group in parliament that i know of.