Explain gene linkage and crossing over using the example of observed trait combinations in offspring.

2a)
Based on the observation that certain combinations of eye colour and wing shape traits appear together much more frequently, it can be inferred that the genes controlling these traits are linked. This means they are located on the same chromosome. The fact that new combinations occasionally appear suggests that they are not perfectly linked and are far enough apart on the chromosome for crossing over to occur.

2b)
The genetic mechanism responsible for the occasional new combinations of traits in the offspring is genetic recombination, specifically crossing over. This process occurs during meiosis, where homologous chromosomes exchange segments of genetic material, leading to new combinations of alleles on the chromatids.