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A hybrid heterozygous at onelocus and obtained from crossing homozygousparents with different alleles at a given locus;for example,Mendels cross between tall(TT) and dwarf (tt) garden peas to give atall monohybrid (Tt). When a monohybrid isselfed,dominant...[继续阅读]
The first sign of embryoformation on the blastoderm of reptiles andbirds and in the inner cell mass of mammals.It usually appears as a longitudinal wrinkle inthe outer layer with a pit (Hensens node) atthe anterior end. This appearance is causedby converg...[继续阅读]
The part of the excretory u-nit (nephron) within the cortex of the verte-brate kidney. It comprises a knot of bloodcapillaries (glomerulus) and a surroundingcup-shaped Bowmans capsule. High pres-sure created within the glomerulus results inthe filtration ...[继续阅读]
The copulatory organs of male carti-laginous fish (e.g.dogfish). They consist of apair of grooved rodlike projections,one oneach side of the cloaca between the pelvic fins.The term may also refer to a pair of tubularoutgrowths on the hind end of the abdom...[继续阅读]
Reproduction in the larval orother juvenile stage by animals exhibitingpermanent neoteny. For example,the axolotl-the larva of a salamander-is able to produceoffspring similar to itself.动物在幼虫期或其他幼年期的生殖,显示为永久的幼态持续。例如美西螈(一种蝾螈幼体)能...[继续阅读]
One of a group of threadlikestructures of different lengths and shapes innuclei of eukaryotic cells. They consist ofDNA with RNA and protein (mostly his-tones) and carry the genes. (The name chro-mosome is also given to the genetic materialof bacteria and...[继续阅读]
The angle between the upper side of aleaf or branch and the shoot bearing it. Leafaxils are the site of lateral (axillary) buds.叶的上表面分支与着生叶或分支的茎干之间的夹角。叶腋是腋芽长出的位点。...[继续阅读]
A chemical that is re-leased from neurone endings to cause eitherexcitation or inhibition of an adjacent neu-rone or muscle cell.It is stored in minutevesicles near the synapse and released whena nerve impulse arrives. In mammals themain neurotransmitters...[继续阅读]
Any of the cells of animal em-bryos that become or produce nerve cells,frequently by unequal mitotic divisions. Al-though many of the cells of the neural tube ofvertebrates will produce nerve cells,the termneuroblast is usually restricted to those cellswh...[继续阅读]
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