Deformation syndrome --- A recognizable pattern of dysmorphic features caused by extrinsic factors that affect the fetus in utero.

变形综合征：子宫中因外部因素影响胎儿而导致的一种畸形。

Degeneracy of the code --- The genetic code is described as degenerate because most of the 20 amino acids are specified by more than 1 of the 64 codons.

简并密码子：三联体第3位碱基不同而编码同一种氨基酸的遗传密码。

Degree of relationship --- The distance between two individuals in a pedigree. First-degree relatives include parents, siblings, and children. Second-degree relatives are aunts and uncles, nephews and nieces, grandparents and grandchildren.

亲等：计算亲属关系亲疏远近的单位。一级亲属包括父母、同胞和子女。二级亲属包括伯姑舅姨、侄子女和祖父母。

Deletion --- The loss of a sequence of DNA from a chromosome. The deleted DNA may be of any length, from a single base to a large part of a chromosome.

缺失：染色体丢失部分片段或DNA分子丢失一些核苷酸的现象。

Denaturation (of DNA) --- The conversion of DNA from the double-stranded to the single-stranded state, usually accomplished by heating to destroy chemical bonds involved in base pairing.

DNA变性：由于物理或化学等因素的影响（常用升温法）使DNA失去生物活性，由双链变成单链的DNA分子。

Deoxyribonucleic acid --- See DNA.

脱氧核糖核酸：参见DNA。

Determination --- During development, the second stage of commitment in which a cell follows its developmental program regardless of whether it is transplanted to a different region of the embryo.

决定：胚胎中的未分化细胞按被定型的命运不可逆地发育成特定类型细胞的过程。

Developmental program --- The process by which a cell in an embryo achieves its fate.

发育程序：胚胎中的细胞发育成为被定型的命运的过程。

Dicentric --- A structurally abnormal chromosome with two centromeres.

双着丝粒：有两个着丝粒的结构异常的染色体。

Dictyotene --- The stage of the first meiotic division in which a human oocyte remains from late fetal life until ovulation.

核网期：第一次减数分裂的一个阶段，从胎儿晚期直到排卵，人类卵母细胞一直处在这个阶段。

Differentiation --- The process whereby a cell acquires a tissue-specific pattern of expression of genes and proteins and a characteristic phenotype.

分化：个体发育过程中同源细胞向不同方向发展的现象，即细胞在结构或功能上由一般发展为特殊的过程。

Diploid --- The number of chromosomes in most somatic cells, which is double the number found in the gametes. In humans, the diploid chromosome number is 46.

二倍体：具有两套染色体组成的细胞或个体。人类的二倍体染色体数目为46.

Discordance --- The situation in which (1) one member of the pair has a certain qualitative trait and the other does not or (2) the relatives have values of a quantitative trait that are at opposite ends of the distribution. See concordance.

不一致性：用于形容2个亲属（1）一个具有某种质量性状而另一个不具有；（2）两者具有的数量性状分别位于正态分布的两端。参见一致性。

Disomy --- See uniparental disomy.

二体：参见单亲二体。

Disruption --- A birth defect caused by destruction of tissue; may be caused by vascular occlusion, a teratogen, or rupture of the amniotic sac with entrapment.

破裂 ：组织破坏引起的出生缺陷；可能由血管闭塞、致畸剂或羊毛囊破裂引起。

Dizygotic (DZ) twins --- Twins produced by two separate ova, separately fertilized. Also called fraternal twins.

二卵双生：由两个受精卵分别发育而成的双生子。又称异卵双生。

DNA (deoxyribonucleic acid) --- The molecule that encodes the genes responsible for the structure and function of living organisms and allows the transmission of genetic information from generation to generation.

DNA（脱氧核糖核酸）：编码生物体结构和功能基因的分子，使得遗传信息代代相传。

DNA ligase --- An enzyme that can form a phosphodiester bond between the deoxyribose backbones of two strands of DNA. See ligation.

DNA连接酶：在DNA复制、修复和重组过程中催化磷酸二酯键合成的酶。参见连接。

DNA methylation --- In eukaryotes, the addition of a methyl residue to the 5-position of the pyrimidine ring of a cytosine base in DNA to form 5-methylcytosine.

DNA甲基化：在真核细胞中，DNA上添入甲基基团的化学修饰现象。

DNA polymerase --- An enzyme that can synthesize a new DNA strand by use of a previously synthesized DNA strand as a template.

DNA聚合酶：以一条DNA链为模板合成另一条新的DNA链时所需要的酶。

Domain --- A region of the amino acid sequence of a protein that can be equated with a particular function.

域 ：蛋白质中具有某种功能的一段氨基酸序列区域。

Dominant --- A trait is dominant if it is phenotypically expressed in heterozygotes. If heterozygotes and homozygotes for the variant allele have the same phenotype, the disorder is a pure dominant (rare in human genetics). If homozygotes have a more severe phenotype than do heterozygotes, the disorder is termed semidominant or incompletely dominant.

显性：杂合状态下性状得以表现，则该形状为显性。若杂合子和纯合子的表型相同，则为完全显性（较罕见）。若纯合子的表型较杂合子严重，则为半显性或不完全显性。

Dominant negative --- A disease-causing allele, or the effect of such an allele, that disrupts the function of a wild-type allele in the same cell.

显性负效：基因的突变产物能抑制野生型基因产物功能的基因突变。

Donor splice site --- The boundary between the 3’ end of an exon and the 5’ end of the next intron. Also called 5’ splice site.

剪接供体位点：外显子3’端和下一个内含子5’端的交界处。又称 5′端剪接位点。

Dosage compensation --- As a consequence of X inactivation, the amount of product formed by the two copies of an X-linked gene in females is equivalent to the amount formed by the single gene in males. See X inactivation.

剂量补偿：在XY性别决定机制的生物中，使性连锁基因在雌、雄性别中有相等或近乎相等的有效剂量的遗传效应。参见X失活。

Double heterozygote --- An individual who is heterozygous at each of two different loci. Contrast with compound heterozygote.

双重杂合子：两对基因都处于杂合状态的个体。相当于复合杂合子。

Double minutes --- Very small accessory chromosomes, a form of gene amplification.

双微体：细胞内基因扩增时染色体某个节段出现相对解螺旋的浅染色区，它们脱离染色体后形成的大量分散、成对的均染小体。

Dyschronic expression --- Expression of a gene at a time when it is not normally expressed.

异时表达：基因在原本不表达的时间表达的现象。

Dysmorphism --- Morphological developmental abnor­malities, as seen in many syndromes of genetic or environmental origin.

畸形：形态发育上的异常变化，如多指症、无脑儿等。

Ecogenetic disorder --- A disorder resulting from the interaction of a genetic predisposition to a specific disease with an environmental factor.

生态遗传病：由共同的环境因素与疾病特异的遗传易感性相互作用导致的疾病。

Ectoderm --- One of the three primary germ layers of the early embryo. Begins as the layer farthest from the yolk sac and ultimately gives rise to the nervous system, the skin, and neural crest derivatives such as craniofacial structures and melanocytes.

外胚层：经过原肠作用后，胚胎具有3个胚层。最外面的上皮细胞层，称为外胚层。外胚层主要形成神经系统、皮肤、神经嵴衍生物如颅面结构和黑色素细胞。

Ectopic expression --- Expression of a gene in places where it is not normally expressed.

异位表达：基因在原本不表达的细胞中表达的现象。

Embryonic stem cell --- A cell derived from the inner cell mass that is self-renewing in culture and, when reintroduced into the inner cell mass of a blastocyst, can repopulate all the tissues of the embryo.

胚胎干细胞：从囊胚期内细胞团分离得到的干细胞，可以分化为体内任何一种类型的细胞。

Empirical risk --- In human genetics, the probability that a familial trait will occur in a family member, based on observed numbers of affected and unaffected individuals in family studies rather than on knowledge of the causative mechanism.

经验风险：在人类遗传学中，某家族成员出现家族性遗传性状的概率。这种概率是基于家系研究得出的，而非发生的机理。

Endoderm --- One of the three primary germ layers of the early embryo. Ultimately gives rise to the gut, liver, and portions of the urogenital system.

内胚层：由上胚层细胞增殖并迁出的部分细胞进入下胚层，并逐渐全部置换了下胚层细胞而形成的新的细胞层。最终发育为肠、肝和部分泌尿生殖系统。

Enhancer --- A DNA sequence that acts in cis (i.e., on the same chromosome) to increase transcription of a gene. The enhancer may be upstream or downstream to the gene and may be in the same or the reverse orientation. Contrast with silencer.

增强子：增强真核基因转录的一类顺式作用因子。相当于沉默子。

Enzymopathy --- A metabolic disorder resulting from deficiency or abnormality of a specific enzyme.

酶病：某一特异酶缺陷或异常所引起的一类疾病。

Epigenetic --- The term that refers to any factor that can affect gene function without change in the genotype. Some typical epigenetic factors involve alterations in DNA methylation, chromatin structure, histone modifications, and transcription factor binding that change genome structure and affect gene expression without changing the primary DNA sequence.

表观遗传学：影响基因功能，但不改变基因型的因素。如DNA甲基化、染色质结构、组蛋白修饰和转录因子结合等可改变基因组的结构，影响基因表达，但不改变主要的DNA序列。

Episome --- A DNA element that either can exist as an autonomously replicating sequence in the cytoplasm or can integrate into chromosomal DNA. Adeno-associated viral vectors, used in gene therapy, are episomes that exist in the cytoplasm for long periods and can, although rarely, be inserted into the nuclear genome.

附加体：细菌染色体外的独立复制子，也可整合在宿主染色体中作为复制子的一部分的遗传单位。如用于基因治疗的腺病毒相关病毒载体。

Euchromatin --- The major component of chromatin. It stains lightly with G banding, decondensing and becoming light-staining during interphase. Contrast with heterochromatin.

常染色质：间期核内染色质丝折叠压缩程度低，处于伸展状态，着色浅的那部分染色质。富含单拷贝DNA序列，有转录活性。相当于异染色质。

Eugenics --- Increasing the prevalence of desirable traits in a population by decreasing the frequency of deleterious alleles at relevant loci through controlled, selective breeding. The opposite is dysgenics.

优生学：通过控制选择性地生育，降低人群中有害基因的频率，增加优秀性状。反义为劣生学。

Eukaryote --- A unicellular or multicellular organism in which the cells have a nucleus with a nuclear membrane and other specialized characteristics. See also prokaryote.

真核生物：核质与细胞质之间存在着明显核膜的生物类型总称。参见原核生物。

Euploid --- Any chromosome number that is an exact multiple of the number in a haploid gamete (n). Most somatic cells are diploid (2n). Contrast with aneuploid.

整倍体：染色体数是染色体基数的倍数的细胞或个体。相当于非整倍体。

Exon --- A transcribed region of a gene that is present in mature messenger RNA.

外显子：真核基因中与成熟mRNA、rRNA或tRNA分子相对应的DNA序列，为编码序列。

Expression profile --- A quantitative assessment of the mRNAs present in a cell type, tissue, or tumor. Often used to characterize a cell, tissue, or tumor in comparison to the expression profile of another cell, tissue, or tumor.

表达谱：细胞、组织或肿瘤中mRNA的定量评估。通常用于细胞、组织或肿瘤间的比较定性。

Expression vector --- A cloning vector engineered to provide for the transcription and translation of a cloned DNA insert so that the host carrying the vector produces the protein encoded by the insert. See vector.

表达载体：携带外源DNA并使之在宿主细胞中表达的载体。参见载体。

Expressivity --- The extent to which a genetic defect is expressed. If there is variable expressivity, the trait may vary in expression from mild to severe but is never completely unexpressed in individuals who have the corresponding genotype. Contrast with penetrance.

表现度：具有相同基因型的个体间基因表达的变化程度。相当于外显率。

Familial --- Any trait that is more common in relatives of an affected individual than in the general popu­lation, whether the cause is genetic, environmental, or both.

家族性：具有家族聚集性的性状，或因遗传因素，或因环境因素。

Fate --- The ultimate destination for a cell that has traveled down a developmental pathway. The embryonic fate map is a complete description of all the fates of all the different parts of the embryo.

命运：在发育过程中，细胞将分化成的细胞类型。胚胎命运图显示了所有细胞的发育前景。

Fetal phase --- Stage of intrauterine development from weeks 9 to 40.

胎儿阶段：子宫内发育第9周至第40周的阶段。

Fetoscopy --- A technique for direct visualization of the fetus.

胎儿镜：直接观察胎儿情况的内窥镜。

FISH --- Fluorescence in situ hybridization. See in situ hybridization.

FISH：荧光原位杂交。参见原位杂交。

Fitness (f) --- The probability of transmitting one’s genes to the next generation compared with the average probability for the population.

适合度（f）：在某种环境条件下，某已知基因型的个体将其基因传递到其后代基因库中的相对能力。

Flanking sequence --- A region of a gene preceding or following the transcribed region.

旁侧序列：结构基因两侧的核苷酸序列。

Founder effect --- A high frequency of a mutant allele in a population founded by a small ancestral group when one or more of the founders was a carrier of the mutant allele.

建立者效应：由少数个体的基因频率决定了他们后代中的基因频率的效应，是一种极端的遗传漂变作用。

Fragile site --- Nonstaining gap in the chromatin of a metaphase chromosome, such as the fragile site at Xq27 in fragile X syndrome.

脆性位点：染色体上可遗传的裂隙或不易着色的区域（一般指Xq27），可诱导产生染色体断裂（导致脆性X综合征）。

Frameshift mutation --- A mutation involving a deletion or insertion that is not an exact multiple of three base pairs and thus changes the reading frame of the gene downstream of the mutation.

移码突变：基因编码区内缺失或增加的核苷酸数目不是3的倍数而造成的读框的移动。

Gain-of-function mutation --- A mutation associated with an increase in one or more of the normal functions of a protein. To be distinguished from novel property mutation.

功能获得突变：导致获得原先没有的功能的基因突变。注意区分新特性突变。

Gamete --- A reproductive cell (ovum or sperm) with the haploid chromosome number.

配子：生物进行有性生殖时产生的生殖细胞（卵子或精子）。正常的配子是单倍性的。

Gatekeeper genes --- Tumor-suppressor genes that directly regulate cell proliferation.

看门基因：直接调控细胞增殖的肿瘤抑制基因。

Gene --- A hereditary unit; in molecular terms, a sequence of chromosomal DNA that is required for the production of a functional product.

基因：遗传信息的基本单位。一般指位于染色体上编码一个特定功能产物（如蛋白质或RNA分子等）的一段核苷酸序列。

Gene dosage --- The number of copies of a particular gene in the genome.

基因剂量：基因组中一个特定基因的拷贝数。

Gene-environment interaction --- Combined action of alleles at one or more loci and nongenetic factors, such as environmental exposures or random events, in causing a complex disease.

基因-环境相互作用：一个或多个基因座上的等位基因与非遗传因素（如环境接触或随机事件等）相互结合发挥作用，引起复杂疾病

Gene family --- A set of genes containing related exons, indicating that the genes have evolved from an ancestral gene by duplication and subsequent divergence.

基因家族：同一物种中结构与功能相似，进化起源上密切相关的一组基因（包含相关的外显子）。