What fraction of opals children would you expect to be able to brag about their blue hair show the cross

Half of the total number of Opals children (50%) will have blue hair.

When an Oompah with purple hair (Pr) marries an Opal with blue hair (rr) out of the four children born two will have blue hair as represented by the below table.

From the table we find that two children are born with the dominant (purple) trait and two with the recessive (blue) trait. Allele is the other word for trait defined by Gregor Mendel in his Law of Segregation. Dominant allele is visible and recessive allele is masked.  

humans, along with other animals and plants, have linear chromosomes that are arranged in pairs within the nucleus of the cell. the only human cells that do not contain pairs of chromosomes are reproductive cells, or gametes, which carry just one copy of each chromosome.

feral cats are estimated to eat tens of millions of native animals each night in australia