| germ cells | The reproductive cells in multicellular organisms. (12 Dec 1998) |
|---|---|
| germ cell tumour | A type of brain tumour. (12 Dec 1998) |
| germ-free animal | An animal which has no microorganisms whatsoever living in or on it. An animal which was born and raised in an isolated environment with no microorganisms in it, such as within a germ-free isolator. (09 Oct 1997) |
| germ-free isolator | A chamber which has absolutely no microorganisms whatsoever living in it, where a germ-free animal can be born and raised. An artificial barrier surrounding a living facility for germ-free animals, which keeps out all microorganisms. (09 Oct 1997) |
| germ-free life | Animals not contaminated by or associated with any foreign organisms. (12 Dec 1998) |
| germ layer | <embryology> A layer of cells produced during the process of gastrulation during the early development of the animal embryo, which is distinct from other such layers of cells, as an early step of cell differentiation. The three types of germ layers are the endoderm, ectoderm, and mesoderm. Diploblastic organisms (e.g. Coelenterates) have two layers, ectoderm and endoderm, triploblastic organisms (all higher animal groups) have mesoderm between these two layers. Germ layers become distinguishable during late blastula/early gastrula stages of embryogenesis and each gives rise to a characteristic set of tissues, the ectoderm to external epithelia and to the nervous system for example: although some tissues contain elements derived from two layers. (18 Nov 1997) |
| germ layers | The three layers of cells comprising the early embryo. (12 Dec 1998) |
| germ layer theory | The developmental biology theory that during early development, the animal embryo divides itself into two or three germ layers, each of which then proceed to further differentiate into organs and tissues specific to that particular layer. (09 Oct 1997) |
| germ line | A group of cells in most multicellular animals which give rise to the reproductive cells. The genome of the animal as contained in these cells, along with any mutations which might arise in them (germinal mutations), can be passed on to offspring. Also can refer to the appearance and conditions of the genome in the germ cells which may be different from within the somatic cells. The development of a germ cell as originating from a cell in a zygote. (09 Oct 1997) |
| germ line gene therapy | The repair or replacement of a defective gene within the gamete-forming tissues, which produces an inheritable change in an organisms genetic constitution. (09 Oct 1997) |
| germ-line mutation | Any detectable and heritable alteration in the lineage of germ cells. Mutations in these cells (i.e., "generative" cells ancestral to the gametes) are transmitted to progeny while those in somatic cells are not. (12 Dec 1998) |
| germ line transformation | Micro injection of foreign DNA into an early embryo, so that it becomes incorporated into the germ line of the individual and thus stably inherited in subsequent generations of transgenic organisms. Typically, the DNA would be a reporter gene or cDNA in a vector such as a transposon, that might also carry a visible marker gene such as eye or coat colour), so that successful transformation could readily be detected. (18 Nov 1997) |
| germ nucleus | <cell biology> The smaller nucleus in ciliate protozoans, fully active in inheritance and passed after meiosis to conjugating pairs. Gives rise to the macronucleus or macronuclei. Genes in the micronucleus are not actively transcribed. (18 Nov 1997) |
| germ plasm | The liquid portion of a gamete (egg or sperm) that contains genetic material. (09 Oct 1997) |
| germ theory | The theory, now a doctrine, that infectious diseases are due to the presence and functional activity of microorganisms within the body. (05 Mar 2000) |