tailieunhanh - Chapter 062. Principles of Human Genetics (Part 27)

Genetic Linkage Genetic linkage refers to the fact that genes are physically connected, or linked, to one another along the chromosomes. Two fundamental principles are essential for understanding the concept of linkage: (1) when two genes are close together on a chromosome, they are usually transmitted together, unless a recombination event separates them (Figs. 62-3, 62-8); and (2) the odds of a crossover, or recombination event, between two linked genes is proportional to the distance that separates them. Thus, genes that are further apart are more likely to undergo a recombination event than genes that are very close together. The. | Chapter 062. Principles of Human Genetics Part 27 Genetic Linkage Genetic linkage refers to the fact that genes are physically connected or linked to one another along the chromosomes. Two fundamental principles are essential for understanding the concept of linkage 1 when two genes are close together on a chromosome they are usually transmitted together unless a recombination event separates them Figs. 62-3 62-8 and 2 the odds of a crossover or recombination event between two linked genes is proportional to the distance that separates them. Thus genes that are further apart are more likely to undergo a recombination event than genes that are very close together. The detection of chromosomal loci that segregate with a disease by linkage can be used to identify the gene responsible for the disease positional cloning and to predict the odds of disease gene transmission in genetic counseling. Polymorphisms are essential for linkage studies because they provide a means to distinguish the maternal and paternal chromosomes in an individual. On average 1 out of every 1000 bp varies from one person to the next. Although this degree of variation seems low identical it means that 3 million sequence differences exist between any two unrelated individuals and the probability that the sequence at such loci will differ on the two homologous chromosomes is high often 70-90 . These sequence variations include VNTRs short tandem repeats STRs and SNPs. Most STRs also called polymorphic microsatellite markers consist of di- tri- or tetranucleotide repeats that can be measured readily using PCR Fig. 62-12 . Characterization of SNPs using DNA chips provides an important new tool for comprehensive analyses of genetic variation linkage and association studies. Although these sequence variations usually have no apparent functional consequences they provide much of the basis for variation in genetic traits. Figure 62-12 CAG repeat length and linkage analysis in multiple endocrine .

• Y học thường thức
• Principles of Human Genetics
• bệnh học và điều trị
• bài giảng bệnh học
• tài liệu y khoa
• Harrisons Internal Medicine
• Biological information
• Lecture Genetics
• Human genetics
• Modern genetic techniques
• Mendels principles
• Mendels principles of heredity