Sex chromosomes and linked genes are not the only genes that are inherited in ways that are unlike the patterns of inheritance that Mendel observed in peas. Genes in mitochondria and chloroplasts also show distinct inheritance patterns. Mitochondria and chloroplasts are ancient organelles of eukaryotic cells originally acquired by the engulfing of prokaryotic cells (Chapter 5). Mitochondria generate ATP that cells use for their chemical energy. Chloroplasts are found only in plant cells and eukaryotic algae. These organelles contain chlorophyll, a green pigment that absorbs light and, in the process of photosynthesis (Chapter 8), produces the sugars that are essential for growth of the plant or algal cells and of the organisms that eat them. Mitochondria and chloroplasts have their own genomes that contain genes for many of the enzymes that carry out the organelles’ functions. Genes present in these genomes move with the organelle during cell division, independent of the segregation of chromosomes in the nucleus.