HD is called an autosomal dominant disorder because only one copy of the defective gene, inherited from one parent, is necessary to produce the disease. The genetic defect responsible for HD is a small sequence of DNA on chromosome 4 in which several base pairs are repeated many, many times.
Carbon dioxide cannot pass through the protective waxy layer covering the leaf (cuticle), but it can enter the leaf through an opening (the stoma; plural = stomata; Greek for hole) flanked by two guard cells. Likewise, oxygen produced during photosynthesis can only pass out of the leaf through the opened stomata.
During photosynthesis (photo = light, synthesis = to make), energy from sunlight is captured with special light-absorbing chemicals (called pigments) and this captured energy is used to make living tissue from the carbon molecules in carbon dioxide gas. Oxygen is released almost as a waste product.