Mitochondria probably came from gram-negative bacteria because they both have double cell membranes. There is an upper limit to the size of single-celled organisms because the surface area-to- volume ratio decreases while the rate of diffusion stays the same so it takes longer for materials to evenly disperse throughout the organism. Linked genes are on the same chromosome and generally in close proximity. Blood type: a produces a glycoprotein (antigen, b produces b glycoprotein, ab produces both a and b glycoprotein (codominance, o is homozygous recessive so doesn"t produce either glycoprotein. Pregnant women can attack fetus" blood if they have negative and the fetus has positive: only occurs if blood is exchanged, generally only happens in second pregnancy because there has been enough time for antibodies to form. Mendel"s work was originally dismissed until thomas hunt morgan did his work with fruit flies that reinforced mendel"s ideas: morgan"s results were not consistent with the idea of independent assortment but.