In the pedigree shown, we can see that 2 parents that are unshaded shapes have 2 children that are shaded shapes. This would be impossible if shaded shapes were dominant and unshaded shapes were recessive. This is because parents that have a recessive trait have 2 of the same alleles. So if 2 parents that both have a recessive trait have a child, the child will definitely have that trait. But we can see that this is not the case, the parents have 2 offspring that have different phenotype from the parents. This must mean the parents are heterozygous, meaning that they both have 2 alleles that are different. The dominant allele masks the recessive allele, so the dominant allele is expressed. In this case, the children inherited 2 recessive alleles, 1 from each parent, making them have a different phenotype from the parents.
You can't see the blood vessels themselves because vision depends on a process that makes it impossible to see things that are stationary with respect to the retina. Light receptors in the retina respond only to changes in light reaching them, not to a steady image.
