Immunoglobulin gene superfamily --- A family of evolutionarily related genes composed of human leukocyte antigen (HLA) class I and class II genes, immunoglobulin genes, T-cell receptor genes, and other genes encoding cell surface molecules.
免疫球蛋白基因超级家族：进化上同源的基因家族，包括HLA I类和II类基因、免疫球蛋白基因、T细胞受体基因以及其它编码细胞表面分子的基因。
Imprinting --- The phenomenon of different expression of alleles depending on the parent of origin. See Prader-Willi syndrome and Angelman syndrome in the text for examples.
印记：遗传物质因来源不同，而出现差别表达的现象。详见正文中的Prader-Willi综合征 和Angelman综合征。
In situ hybridization --- Mapping a gene or segment of DNA by molecular hybridization to a chromosome spread or cell nucleus on a slide by use of a labeled DNA sequence as a probe corresponding to the gene or DNA segment to be mapped. Usually involves fluorescently labeled probes, in which case it is referred to as fluorescence in situ hybridization (FISH).
原位杂交：用标记的单链DNA或RNA探针显示出与其互补的核苷酸序列在组织或细胞中的位置。通常使用的标记为荧光素。
Inborn error of metabolism？ific protein defect produces a metabolic block that may have pathological consequences.
先天性代谢缺陷：遗传原因造成的蛋白质分子（一般指酶）结构或数量的异常引起的疾病。
Inbreeding --- The mating of closely related individuals. The progeny of close relatives are said to be inbred. (Note that some consider the term inbreeding to be pejorative when it is applied to human populations.)
近交：有亲缘关系的个体间的交配。（注意，本词应用到人群中可能产生反感。）
Incompletely dominant --- A trait that is inherited in a dominant manner but is more severe in a homozygote than in a heterozygote (synonym: semidominant).
不完全显性：杂合子表现出的性状介于相应的两种纯合子性状之间的现象（同义词：半显性）。
Indel --- A polymorphism defined by the presence or absence of a segment of DNA, ranging from one base to a few hundred base pairs. Includes simple indels, microsatellites, and minisatellite polymorphisms.
插缺：两个匹配的DNA序列间有插入和缺失的位置。包括简单插缺、微卫星和小卫星多态性。
Index case --- The family member affected with a genetic disorder who is the first to draw attention to a pedigree. See proband.
索引病例：一个家系中最先被发现具有某个特异性状的个体。参见先证者。
Induction --- The determination of the fate of one region of an embryo by extracellular signals from a second, usually neighboring, region.
诱导：胚胎中的一个区域影响到另一个区域，使其沿着一条新途径进行分化。
In-frame deletion --- A deletion that does not destroy the normal reading frame of the gene.
整码缺失：基因内的核苷酸数目为3的倍数而不造成读框改变的缺失。
Inner cell mass --- A small group of cells within the preimplantation mammalian embryo that will become the primitive ectoderm (or epiblast) after implantation and, ultimately, give rise to the embryo proper and not the placenta.
内细胞团：哺乳动物植入前胚胎的一组细胞，将发育成为原始外胚层，最终成为胚体而非胎盘。
Insert --- In molecular biology, a fragment of foreign DNA cloned into a vector.
插入片段：在分子生物学中，指插入载体分子或基因组中的一段外源DNA序列。
Insertion --- A chromosomal abnormality in which a DNA segment from one chromosome is inserted into another chromosome.
插入：在DNA或RNA链中增加一个或多个额外核苷酸的过程。
Intergenic complementation --- The ability of cells from patients with similar phenotypes due to mutations in different genes to correct one another.
基因间互补：由于不同基因的突变相互之间的矫正，而导致患者表型相同。
Intergenic DNA --- The untranscribed DNA of unknown function that makes up a large proportion of the total DNA in the genome.
基因间DNA：DNA分子中除了通常意义上的基因以外的核苷酸组成，为DNA分子中的绝大部分，不转录。功能尚不清楚。
Interphase --- The stage of the cell cycle between two successive mitoses.
间期：细胞周期从一次有丝分裂结束至下一次有丝分裂开始间的时期。
Intervening sequence --- See intron.
间插序列：参见内含子。
Intron --- A segment of a gene that is initially transcribed but then removed from within the primary RNA transcript by splicing together the sequences (exons) on either side of it.
内含子：初级转录物中无编码意义而被切除的序列。相当于外显子。
Inversion --- A chromosomal rearrangement in which a segment of a chromosome is reversed end to end. If the centromere is included in the inversion, the inversion is pericentric; if not, it is paracentric.
倒位：染色体结构变异的一种。染色体上的两个断裂点间的断片，倒转后又重新连接。若断片包括着丝粒，则称为臂间倒位，否则称为臂内倒位。
In vitro fertilization --- A reproductive technology in which sperm are allowed to fertilize an egg in tissue culture and the fertilized eggs are then introduced back into the uterus to allow implantation.
体外受精：在体外进行精卵结合的生殖技术。
Isochromosome --- An abnormal chromosome in which one arm is duplicated (forming two arms of equal length, with the same loci in reverse sequence) and the other arm is missing.
等臂染色体：着丝粒在染色体中间，两臂等长的染色体。
Isodisomy --- See uniparental disomy.
等二体：参见单亲二体。
Isolate --- A subpopulation in which matings take place exclusively or usually with other members of the same subpopulation.
隔离：不能进行基因交流或基因交流显著降低的亚群体。
Isolated case --- An individual who is the only member of his or her kindred affected by a genetic disorder, either by chance or by new mutation. See also sporadic.
单发病例：一个家系中唯一的患病个体，可由上代遗传基因决定，也可由于新突变产生。参见散发。
Karyotype --- The chromosome constitution of an individual. The term is also used for a photomicrograph of the chromosomes of an individual systematically arranged and for the process of preparing such a photomicrograph.
核型：细胞分裂中期染色体的数目、大小和形态特征的总汇。
kb (kilobase) --- A unit of 1000 bases in a DNA or RNA sequence.
Kb：DNA或RNA序列中1000个bp的单位。
Kindred --- An extended family.
家族：扩大了的家系。
Kinetochore --- A structure at the centromere to which the spindle fibers are attached.
动粒：纺锤体微管在着丝粒两侧的附着处，与染色体分离密切相关。
Library --- In molecular biology, a collection of recombinant clones that contain a sample of the DNA or RNA (as cDNA) of a tissue.
文库：在分子生物学中，指包含某组织的DNA或RNA（cDNA）序列的重组克隆的集合。
Ligation --- In molecular biology, the process of joining two double-stranded DNA molecules to form a recombinant DNA molecule, by means of phosphodiester bonds, with use of the enzyme DNA ligase.
连接：单链核酸分子间的共价连接反应。尤指双链DNA的一条链上切口两端的两个紧邻碱基间形成磷酸二酯键的反应。
LINE sequences --- A class of repetitive DNA made up of long interspersed nuclear elements, up to 6 kb in length, occurring in several hundred thousand copies in the genome (also called L1 family).
长散在重复序列：以散在方式分布于基因组中的较长的重复DNA序列。最长可达6kb（又称L1家族）。
Lineage --- The progeny of a cell, generally determined by experimentally labeling the cell so that all of its descendants can be identified. See clone.
谱系：某细胞的繁衍，通常用标记以识别。参见克隆。
Linkage --- Genes on the same chromosome are linked if they are transmitted together in meiosis more frequently than chance would allow. Compare with synteny.
连锁：位于同一条染色体上的基因一起遗传的现象。参见同线性。
Linkage analysis --- A statistical method in which the genotypes and phenotypes of parents and offspring in families are studied to determine whether two or more loci are assorting independently or exhibiting linkage during meiosis.
连锁分析：研究某一基因与其它基因连锁关系的一种统计学方法。
Linkage disequilibrium --- The occurrence of specific combinations of alleles in coupling phase at two or more linked loci more frequently than expected by chance from the frequency of the alleles in the population.
连锁不平衡：两个或以上处于互引连锁相的基因座的等位基因发生特异组合的几率，比群体中期望的等位基因频率更为常见的现象。由于基因座间的连锁关系或其他原因（选择、突变、群体混杂等），群体中的配子和基因型频率偏离随机组合的期望值。
Linkage disequilibrium block？age disequilibrium with each other. Usually occupies a region of the genome from a few kilobases to a few dozen kilobases in length.
连锁不平衡模块：一组多态性标记，其上的基因之间连锁不平衡。一般长约几kb～几十kb。
Linkage map --- A chromosome map showing the relative positions of genes and other DNA markers on the chromosomes, as determined by linkage analysis.
连锁图：连锁基因或遗传标记在染色体上的相对位置的线性图。
Locus --- The position occupied by a gene on a chromosome. Different forms of the gene (alleles) may occupy the locus.
基因座：指一个基因在染色体上所占的位置。基因的不同形式即等位基因。
Locus control region (LCR) --- A DNA domain, situated outside a cluster of structural genes, responsible for the appropriate expression of the genes within the cluster.
基因座控制区（LCR）：一段DNA域，位于结构基因簇之外，调控基因的适时表达。
Locus heterogeneity --- The production of identical phenotypes by mutations at two or more different loci.
基因座异质性：不同基因座的突变导致了相同或相似表型的效应。
LOD score --- A statistical method that tests genetic marker data in families to determine whether two loci are linked. The lod score is the logarithm of the odds in favor of linkage. By convention, a LOD score of 3 (odds of 1000 : 1 in favor) is accepted as proof of linkage and a LOD score of -2 (100 : 1 against) as proof that the loci are unlinked.
优势对数计分：最常用、最有效的连锁分析计算法，是一种利用对数概率比值来检测某一家系中有关遗传性状分布情况的方法。若LOD值为3，肯定连锁，若为-2，否定连锁。
L1 family --- See LINE sequences.
L1家族：参见长散在重复序列。
Loops --- Arrangement of chromatin, packaged as solenoids, attached to the chromosome scaffold. Thought to be a structural or functional unit of chromosomes.
袢环：染色质的一种形态，螺旋管状，与染色体支架有关。被认为是染色体的功能单位。
Loss-of-function mutation --- A mutation associated with a reduction or a complete loss of one or more of the normal functions of a protein.
功能失去突变：导致丢失原有功能的基因突变。
Loss of heterozygosity (LOH) --- Loss of a normal allele from a region of one chromosome of a pair, allowing a defective allele on the homologous chromosome to be clinically manifest. A feature of many cases of retinoblastoma, breast cancer, and other tumors due to mutation in a tumor-suppressor gene.
杂合性丢失（LOH）：一对杂合的等位基因变成纯合状态，从而导致临床症状的现象。常见于视网膜母细胞瘤、乳腺癌和其它因为肿瘤抑制基因突变而引起的癌症。
Lyonization --- Term used for the phenomenon of X inactivation, which was first described by the geneticist Mary Lyon. See X inactivation.
莱昂作用：X染色体在遗传上失活的过程。参见X失活。
Major histocompatibility complex (MHC) --- The complex locus on chromosome 6p that includes the highly polymorphic human leukocyte antigen (HLA) genes.
主要组织相容性复合体（MHC）：位于6p的高度多态性复杂基因座（包括HLA基因）。
Maleficence --- Behavior that harms others. Avoidance of maleficence is one of the cardinal principles of ethics. See beneficence.
恶行：伤害他人的行为。避免行恶是道德伦理的准则之一。参见慈善。
Male-to-male transmission --- A pattern of inheritance of a trait from a father to all of his sons and none of his daughters (also referred to as holandric inheritance).
男-男遗传：父亲将性状遗传给所有的儿子，而不遗传给女儿的一种遗传方式。即限雄遗传
Malformation syndrome --- A recognizable pattern of dysmorphic features having a single cause, either genetic or environmental.
畸形综合征：单个原因（遗传或环境因素）引起的畸形。
Manifesting heterozygote --- A female heterozygous for an X-linked disorder in whom, because of nonrandom X inactivation, the trait is expressed clinically with approximately the same degree of severity as in hemizygous affected males.
显示杂合子：X-连锁遗传病的女性杂合子，由于非随机的X失活，临床症状得以表达。其严重程度与半合子男性相似。
Maternal inheritance --- The transmission of genetic information only through the mother.
母系遗传：只通过母亲传递遗传物质。
Maternal serum screening --- Laboratory test that relies on measurement of the levels of particular substances, such as alpha-fetoprotein, human chorionic gonadotropin, and unconjugated estriol, in a pregnant woman’s blood to screen for fetuses affected with certain trisomies or with neural tube defects.
母体血清筛查：检测某些特异物质含量的一种实验室检测方法。如检测孕妇血中的甲胎蛋白、人类绒毛膜促性腺激素和非结合性雌三醇，以筛查胎儿是否为三体或神经管缺陷。
Mb (megabase) --- A unit of 1,000,000 bases or base pairs in genomic DNA.
Mb：基因组DNA中一百万个碱基对的单位。
Meiosis --- The type of cell division occurring in the germ cells, by which gametes containing the haploid chromosome number are produced from diploid cells. Two meiotic divisions occur: meiosis I and meiosis II. Reduction in chromosome number takes place during meiosis I.
减数分裂：生殖细胞连续进行两次核分裂，而染色体只复制一次，由此产生四个单倍体细胞（配子），染色体数目减半的特殊细胞分裂方式。
Mendelian --- Patterns of inheritance that follow the classic laws of Mendel: autosomal dominant, autosomal recessive, and X-linked. See single-gene disorder.
孟德尔遗传：遵循孟德尔遗传定律的典型方式：常染色体显性、常染色体隐性和X-连锁遗传。参见单基因遗传病。
Mesoderm --- The middle germ layer in the early embryo; the source of cells that go on to make bones, muscles, connective tissue, heart, hematopoietic system, kidney, and other organs.
中胚层：原肠胚形成过程中，由上胚层细胞增殖产生的一部分细胞在上、下胚层之间形成的第三层细胞。通常形成骨骼、肌肉、结缔组织、心脏、造血系统、肾脏和其它器官。
Messenger RNA (mRNA) --- An RNA, transcribed from the DNA of a gene, that directs the sequence of amino acids of the encoded polypeptide.
信使RNA（mRNA）：携带从DNA编码链得到的遗传信息，在核糖体上翻译产生多肽的RNA。
Metacentric --- A type of chromosome with a central centromere and arms of apparently equal length.
中着丝粒染色体：着丝粒位于中间，两臂长度明显相当的一种染色体。
Metaphase --- The stage of mitosis or meiosis in which the chromosomes have reached their maximal condensation and are lined up on the equatorial plane of the cell, attached to the spindle fibers. This is the stage at which chromosomes are most easily examined.
中期：细胞有丝分裂或减数分裂时的一个时期。染色体充分凝聚，核膜破裂后，纺锤体与着丝粒连接，染色体逐渐排列在赤道板上。
Metastasis --- Spread of malignant cells to other sites in the body.
转移：恶性细胞扩散到身体其他部位的现象。
Methemoglobin --- The oxidized form of hemoglobin, containing iron in the ferric rather than the ferrous state, that is incapable of binding oxygen.
高铁血红蛋白：血红蛋白的氧化形式，含正铁离子而非亚铁离子，不能携带氧。
MicroRNA --- A particular class of noncoding RNAs that are processed into short interfering RNAs (siRNA), double stranded RNAs approximately 22 nucleotides in length, that affect mRNA stability or translation. siRNAs are involved in gene regulation in development and differentiation.
微 RNA ：一种非编码 RNA ，与小干扰 RNA （ siRNA ）有关，为双链 RNA ，长约 22 个核苷酸，影响 mRNA 的稳定和翻译。 siRNA 与发育和分化的基因调控有关。