Dorsal
Pertaining to or situated near the back; opposite of ventral.
Dorsoventrally
Relating to or involving, or extending along the axis joining the dorsal and ventral sides.
Double circulation
A circulation scheme with separate pulmonary and systemic circuits, which ensures vigorous
blood flow to all organs.
Double fertilization
A mechanism of fertilization in angiosperms, in which two sperm cells unite with two cells in
the embryo sac to form the zygote and endosperm.
Double helix
The form of native DNA, referring to its two adjacent polynucleotide strands wound into a
spiral shape.
Down syndrome
A human genetic disease resulting from having an extra chromosome 21, characterized by
mental retardation and heart and respiratory defects.
Dorsifixed
Attached at the or by the back to a plant or plant part.
Duodenum
The first section of the small intestine, where acid chyme from the stomach mixes with
digestive juices from the pancreas, liver, gallbladder, and gland cells of the intestinal wall.
Duplication
An aberration in chromosome structure resulting from an error in meiosis or mutagens;
duplication of a portion of a chromosome resulting from fusion with a fragment from a
homologous chromosome.
Duramen (Heart wood)
The older inactive central wood of a tree or woody plant; usually darker and denser than the
surrounding sapwood
Dynein
A large contractile protein forming the sidearms of microtubule doublets in cilia and flagella.
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