tailieunhanh - Chapter 062. Principles of Human Genetics (Part 14)

Transmission of Genetic Disease Origins and Types of Mutations A mutation can be defined as any change in the primary nucleotide sequence of DNA regardless of its functional consequences. Some mutations may be lethal, others are less deleterious, and some may confer an evolutionary advantage. Mutations can occur in the germline (sperm or oocytes); these can be transmitted to progeny. Alternatively, mutations can occur during embryogenesis or in somatic tissues. Mutations that occur during development lead to mosaicism, a situation in which tissues are composed of cells with different genetic constitutions. If the germline is mosaic, a mutation can be. | Chapter 062. Principles of Human Genetics Part 14 Transmission of Genetic Disease Origins and Types of Mutations A mutation can be defined as any change in the primary nucleotide sequence of DNA regardless of its functional consequences. Some mutations may be lethal others are less deleterious and some may confer an evolutionary advantage. Mutations can occur in the germline sperm or oocytes these can be transmitted to progeny. Alternatively mutations can occur during embryogenesis or in somatic tissues. Mutations that occur during development lead to mosaicism a situation in which tissues are composed of cells with different genetic constitutions. If the germline is mosaic a mutation can be transmitted to some progeny but not others which sometimes leads to confusion in assessing the pattern of inheritance. Somatic mutations that do not affect cell survival can sometimes be detected because of variable phenotypic effects in tissues . pigmented lesions in McCune-Albright syndrome . Other somatic mutations are associated with neoplasia because they confer a growth advantage to cells. Epigenetic events heritable changes that do not involve changes in gene sequence . altered DNA methylation may influence gene expression or facilitate genetic damage. With the exception of triplet nucleotide repeats which can expand see below mutations are usually stable. Mutations are structurally diverse they can involve the entire genome as in triploidy one extra set of chromosomes or gross numerical or structural alterations in chromosomes or individual genes Chap. 63 . Large deletions may affect a portion of a gene or an entire gene or if several genes are involved they may lead to a contiguous gene syndrome. Unequal crossing-over between homologous genes can result in fusion gene mutations as illustrated by color blindness Chap. 29 . Mutations involving single nucleotides are referred to as point mutations Fig. 62-5 . Substitutions are called transitions if a purine is .

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• Principles of Human Genetics
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• Harrisons Internal Medicine
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• Mendels principles
• Mendels principles of heredity