Preface ........................................................ xi
Acknowledgements ............................................... xi
Abbreviations ................................................. xii
1 Organization of DNA .......................................... 1
1.1 Chromosome structure and the DNA molecule ............... 2
1.2 DNA replication 6 Principle of replication ............. 6
Eukaryotic replication .................................. 7
1.3 The cell cycle .......................................... 8
1.4 Mitosis and meiosis ..................................... 9
Mitosis ................................................. 9
Meiosis ................................................ 11
1.5 Genes .................................................. 14
The nuclear genome ..................................... 14
The mitochondrial genome ............................... 15
1.6 Chromosomes and chromatin .............................. 15
Heterochromatin and euchromatin ........................ 16
1.7 Chromosomes and nomenclature ........................... 17
Suggested further reading ................................... 18
Self-assessment questions ................................... 18
2 How normal genes work ....................................... 19
2.1 Gene expression ........................................ 20
2.2 Transcription .......................................... 20
2.3 Translation ............................................ 21
2.4 Control of gene expression ............................. 23
Transcriptional control ................................ 25
Post-transcriptional regulation ........................ 28
Translational control .................................. 28
Other methods of gene control .......................... 29
2.5 Epigenetics and genomic imprinting ..................... 30
Genomic imprinting ..................................... 31
2.6 DNA repair ............................................. 34
2.7 Immunogenetics ......................................... 36
The immune system ...................................... 36
В cells ................................................ 37
T cells ................................................ 39
2.8 Mitochondrial genes .................................... 40
2.9 Developmental genetics ................................. 40
Embryonic pattern formation ............................ 42
2.10 Sex differentiation .................................... 45
Sexual development in the fetus ........................ 45
Other genes involved in sexual differentiation ......... 46
2.11 Summary ................................................ 46
Suggested further reading ................................... 47
Self-assessment questions ................................... 47
3 Mechanisms of disease ....................................... 49
3.1 Mutations .............................................. 50
Triplet repeats/dynamic mutations ...................... 53
3.2 Alteration of gene control ............................. 55
Positional effects ..................................... 55
Abnormal dosage and haploinsufficiency ................. 56
Skewed X-inactivation patterns ......................... 57
Epigenetic pathology ................................... 58
Methylation, epigenetic alterations and cancer ........ 58
Methylation and imprinting disorders ................... 58
3.3 DNA repair defects in human disease .................... 59
Xeroderma pigmentosum .................................. 59
Other disorders of DNA repair and replication .......... 60
3.4 Immunogenetic diseases ................................. 60
3.5 Mitochondrial mutations ................................ 61
3.6 Developmental changes .................................. 62
Growth factor receptors ................................ 62
Hedgehog signalling pathway ............................ 63
Homeobox genes ......................................... 64
3.7 Sex determination ...................................... 64
Sex reversal ........................................... 64
Evidence of other genes influencing sex
determination .......................................... 65
Other examples of abnormalities of sexual
differentiation ........................................ 65
3.8 Summary ................................................ 66
Suggested further reading ................................... 67
Self-assessment questions ................................... 67
4 Patterns of inheritance ..................................... 69
4.1 Classical genetics ..................................... 70
Mendel's laws .......................................... 70
4.2 Linkage ................................................ 71
4.3 Recombination .......................................... 71
4.4 The application of Mendel's laws to human genetics ..... 72
4.5 Pedigrees .............................................. 73
4.6 Mendelian inheritance patterns ......................... 74
Autosomal dominant inheritance ......................... 74
Autosomal recessive inheritance ........................ 77
X-linked recessive inheritance ......................... 78
X-linked dominant inheritance .......................... 79
Fragile X - a special case? ............................ 80
Y-linked inheritance ................................... 80
4.7 Other problems with inheritance ........................ 80
Heterogeneity .......................................... 80
Parental origin ........................................ 82
New mutations .......................................... 82
Germline mosaicism ..................................... 82
4.8 Mitochondrial inheritance .............................. 82
4.9 Gradation of inheritance ............................... 83
4.10 Population genetics .................................... 84
The Hardy-Weinberg equilibrium ......................... 85
4.11 Linkage and Lod scores ................................. 87
4.12 Bayes'theorem .......................................... 90
4.13 Summary ................................................ 93
Suggested further reading ................................... 93
Self-assessment questions ................................... 93
5 Cytogenetics ................................................ 95
5.1 The human karyotype .................................... 96
Ploidy ................................................. 97
5.2 Preparing chromosomes .................................. 98
pH ..................................................... 99
Temperature ............................................ 99
5.3 Chromosome analysis ................................... 103
Describing chromosomes - band nomenclature ............ 107
5.4 Types of chromosome abnormalities ..................... 108
Autosomal aneuploidies ................................ 109
Chromosome abnormalities in spontaneous abortions ..... 109
Structural abnormalities .............................. 111
Translocations ........................................ 112
Deletions ............................................. 117
Isochromosomes ........................................ 120
Inversions ............................................ 122
Ring chromosomes ...................................... 124
Duplications .......................................... 125
Complex chromosome abnormalities ...................... 125
Extra structurally abnormal chromosomes ............... 126
5.5 The sex chromosomes ................................... 127
XY pairing ............................................ 127
Sex determination ..................................... 127
Turner syndrome ....................................... 128
Klinefelter syndrome .................................. 128
Other aneuploidies of sex chromosomes ................. 128
Genes on the X chromosome ............................. 129
Replication banding ................................... 130
X;autosome translocations ............................. 130
Sex reversal .......................................... 131
Mosaicism ............................................. 131
Suggested further reading .................................. 133
Self-assessment questions .................................. 133
6 Molecular cytogenetics ..................................... 135
6.1 Introduction .......................................... 136
6.2 Fluorescence in situ hybridization .................... 136
Probes ................................................ 137
Basic principles of FISH .............................. 137
Filters and microscopy ................................ 140
Interphase FISH ....................................... 141
6.3 Types of FISH probes .................................. 141
Single copy probes .................................... 141
Probes for small chromosome rearrangements ............ 143
Centromere and repeat sequence probes ................. 146
Chromosome painting of entire chromosomes ............. 151
6.4 Comparative genomic hybridization ..................... 152
Chromosomal comparative genomic hybridization ......... 154
Array comparative genomic hybridization ............... 154
Analysis and interpretation of array CGH results ...... 155
Bioinformatics ........................................ 158
The use of array CGH in clinical cytogenetics ......... 160
The use of arrays in the investigation of children
with learning difficulties ............................ 160
Investigation of apparently balanced rearrangements ... 162
The use of array CGH in prenatal diagnosis ............ 162
Infertility and recurrent abortions ................... 163
Cancer ................................................ 163
6.5 Summary ............................................... 164
Suggested further reading .................................. 164
Self-assessment questions .................................. 165
7 Molecular genetics ......................................... 167
7.1 Introduction to molecular genetics .................... 168
7.2 Southern blotting ..................................... 168
DNA probes ............................................ 169
Restriction enzymes ................................... 170
General principles of gel electrophoresis ............. 172
Polymorphisms ......................................... 173
Principles of Southern blotting ....................... 173
Steps involved in Southern blotting ................... 174
Interpretation of Southern blots ...................... 179
Gene tracking ......................................... 183
"Informativeness" ..................................... 184
7.3 The polymerase chain reaction ......................... 185
Principles of PCR ..................................... 185
Details of a typical PCR method ....................... 187
Applications of PCR ................................... 188
Interpretation of PCRs ................................ 189
Automated screening strategies using PCR .............. 196
Detection of large duplications and deletions ......... 198
7.4 Summary ............................................... 204
Suggested further reading .................................. 204
Self-assessment questions .................................. 204
8 Cancer genetics ............................................ 205
8.1 Introduction to cancer cytogenetics ................... 206
8.2 Oncogenes ............................................. 207
Function of proto-oncogenes ........................... 207
How oncogenes exert their effect ...................... 208
Summary ............................................... 210
8.3 Tumour suppressor genes ............................... 210
Knudson's two-hit hypothesis .......................... 211
Loss of heterozygosity ................................ 212
Neuro-oncology ........................................ 213
8.4 Apoptosis ............................................. 214
The role of p53 ....................................... 214
p53 and cancer ........................................ 216
PTCH as a tumour suppressor ........................... 216
Summary ............................................... 217
8.5 Mismatch repair genes ................................. 217
8.6 Cytogenetics and the investigation of malignancy ...... 218
Cytogenetics and the haematological malignancies ...... 221
The relationship between chromosome abnormalities
and cancer ............................................ 232
8.7 Cancer and the family ................................. 235
Inherited breast cancer ............................... 236
Testing for BRCA mutations ............................ 237
8.8 Tbe multistep nature of cancer ........................ 238
8.9 Summary ............................................... 239
Suggested further reading .................................. 240
Self-assessment questions .................................. 241
9 Prenatal diagnosis and screening ........................... 243
9.1 Introduction .......................................... 244
9.2 Prenatal diagnosis .................................... 245
Identification of pregnancies at risk ................. 245
9.3 Population screening .................................. 250
The limitations of screening .......................... 253
Prenatal screening in pregnancy ....................... 254
Combining screening tests ............................. 259
Second trimester testing .............................. 260
Factors affecting maternal serum screening ............ 261
9.4 Methods of prenatal diagnosis ......................... 261
Methods for the rapid detection of Down syndrome ...... 263
Problems associated with prenatal diagnosis ........... 264
Other problems of interpretation of prenatal
chromosome results .................................... 265
Other screening before or during pregnancy ............ 266
Screening for haemoglobin disorders ................... 267
Newborn blood spot screening .......................... 267
9.5 Alternatives to prenatal diagnosis .................... 270
Assisted reproduction ................................. 270
Pre-implantation genetic diagnosis .................... 272
Cell-free nucleic acid for non-invasive prenatal
diagnosis ............................................. 272
9.6 The future ............................................ 274
Suggested further reading .................................. 274
Self-assessment questions .................................. 275
10 Genetic counselling and genetics and society ............... 277
10.1 Introduction .......................................... 278
10.2 Genetic counselling ................................... 279
Establishing the diagnosis ............................ 281
Calculating the risk .................................. 282
Discussing the options ................................ 282
Genetic testing of children ........................... 283
Screening for genetic carrier status .................. 284
Consanguinity ......................................... 285
Unexpected information when taking the family tree .... 286
Role of genetic testing in adoption ................... 287
Investigating paternity ............................... 287
10.3 Storage of genetic material - planning for the
future ................................................ 289
10.4 Protecting genetic information - consent and
confidentiality in clinical practice .................. 290
Consent ............................................... 290
Data Protection Act 1998 .............................. 292
10.5 Genetic susceptibility ................................ 293
Familial cancer ....................................... 293
Genetic registers ..................................... 295
10.6 Genetic information and the insurance industry ........ 295
10.7 Gene therapy .......................................... 296
10.8 Over-the-counter genetic tests ........................ 297
10.9 Babies by design - the ethics of genetic choice ....... 298
10.10 Pharmacogenetics and personalized medicine ........... 298
10.11 Genetic 'identity cards' and horoscopes .............. 300
10.12 Disability and genetics .............................. 300
10.13 The future ........................................... 301
Suggested further reading .................................. 301
Self-assessment questions .................................. 301
Answers to self-assessment questions .......................... 303
Appendices
Glossary of disorders ...................................... 309
Internet resources ......................................... 318
Index ......................................................... 323
|
