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1、Single-gene disorders1、TerminologyAllele：is alternative variations of genetic information at a particular locus on a choromosome. Genotype: is the set of alleles that make up a persons genetic constitution at a single locus. Phenotype:is the observable expression of a genotype as a morphological, cl
2、inical or molecular trait. Homozygous:when a person has a pair of identical alleles in a locus,he is said to be homozygous.Heterozygous:when the alleles are different ,he is said to be heterozygous.Dominant:with a dominant genetic disorder ,one abnormal copy of the gene will cause the disease.Recess
3、ive:both copies of the gene must be abnormal in order for a person to be affected by the Disease.Pedigree:is a family tree which made up by symbols and lines,represent a patients genetic family History.Pedigree analysis: （1）Information of family members more than three generations 家系越大越好，患者与正常人的信息都采
4、（2）Information verified by genetic consultant（3）Investigating the death cause, death age, consanguineous marriage, fetal death, abortion, neonatal death（4）Determine the mode of inheritance:遗传方式 dominant, recessive, partial dominance, sex-linked, autosomal, mitochondrial, maternal effect.母体效应（5）Deter
5、mine the probability of an affected offspring for a given cross.2、Patterns of single gene disorders （1）Factors determined the classificationChromosome locationDominant or recessive （2）Basic patterns of single gene disordersDominant RecessiveAutosomal Autosomal dominant (AD) Autosomal recessive (AR)X
6、-linked X-linked dominant (XD) X-linked recessive (XR)Y-linked Y-linked3、Autosomal Recessive (AR) Definition：AR are presented only in individuals who are homozygous for the mutant gene on autosome. Carrier (Aa )：An individual who carries one gene for a particular recessive trait. A carrier does not
7、express the trait, while they could have an affected offspring when mating with another carrier. Pedigree Characteristics of AR（1）Affects both sexes equally（2）A child of unaffected carrier parents has 25% risk of disease（3）Few affecters, usually only in one generation（4）Increased risk in consanguine
8、ous mating Coefficient of relationship 亲缘系数The probability that any two individuals share a given gene at a random locus from a common ancestor. Consanguineous mating 近亲婚配Consanguineous mating could increase the risk of affected. More rarer the autosome recessive is, more higher the risk inceresed.
9、Disease: PKU, Albinism 4、 Autosomal Dominant (AD)Definition:AD diseases are those in which a single copy of a mutant gene on autosome is enough for the trait to be expressed or shown.Subtypes of AD:（1）Complete dominance Brachydactyly 短指症The phenotype of the heterozygote (Aa ) will be indistinguishab
10、le from the phenotype of the homozygous (AA ) dominant.杂合子患者和纯合子患者表型没有区别Pedigree Characteristics： Each affected individual has one affected parent. Passed in a vertical fashion 垂直传递 50% of offspring are affected 50% of sibs 同胞 are affected. Males and females are affected with equal probability（2）Inc
11、omplete dominance (semi-dominance) Achondroplasia 软骨发育不全 (MIM 100800)The phenotype of the heterozygote (Aa) will be intermediate between the phenotypes of the two homozygotes (AA or aa ). （3）Codominance 共显性 ABO blood groupBoth alleles will be completely expressed in the heterozygote, and the individ
12、ual has a different phenotype with either of the homozygote. （4）Irregular dominance Polydactyly, postaxialSometime the heterozygote (Aa ) will not show the phenotypes of dominant allele, and sometimes they will show different clinical symptoms. Penetrance 外显率：is defined as the percentage of individu
13、als with a given genotype who exhibit the phenotype associated with that genotype. The individuals without the phenotypes were called forme fruste.顿挫型 Irregular dominance Forme frusteSkipped generationExpressivity 表现度 ：Expressivity is the severity of expression of the phenotype among individuals wit
14、h the same disease-causing genotype. 基因型相同有不同的表型 Individuals with the same principal gene shows different phenotypes.（5）Delayed dominance 延迟显性 Huntington diseaseNot all genetic disorders are congenital 先天的, some are expressed at a characteristic age and others at variable ages. 动态突变5、X-linked Inheri
15、tanceX-linked diseases are single gene disorders that reflect the presence of defective 错误的 genes on the X chromosome. Hemizygous 半合子：describes a diploid male who has only one allele on the X-chromosome rather than the usual two in a diploid female.Criss-cross inheritance 交叉遗传：Male can only receive
16、alleles on the X-chromosome from his mother and transmits it to his daughter.X-linked recessive inheritance (XR)：a recessive faulty 有缺陷的 gene that is located on the X Chromosome Eg: Hemophilia A 血友病, Red-green colorblindnessPedigree Characteristics of XR（1）Affects almost exclusively 专门地 men（2）Affected men born from carrier mother, with 50% risk to be affected（3）No male to male transmissio
