Suppose synapsis occurred between two homologous chromosomes, and one had alleles for blue eyes and brown hair where the other had alleles for green eyes and blond hair. how many different combinations of these alleles would be possible?

Four different combinations.

Explanation:

Synapsis may be defined as the pairing of the homologous chromosome during the meiosis cell division. This synapsis can result in the chnage in the phenotype and genotype of the organisms.

The crossing over between the alleles for blue eyes and brown hair and alleles for green eyes and blond hair. The outer chromatids are unaffected and same as parent whereas the two inner chromatids are affected. Four different possible combinations are blue eyes/brown hair , blue eyes/blonde hair, green eyes/blonde hair and green eyes/brown hair .

Thus, the answer is four different combinations.

they float because they are less dense than the water itself

something denser than water, like a rock, will sink to the bottom