CLINICAL GENETICS

A SHORT INTRODUCTION

BY

DR.C.GANESAN M.D.,

PROFESSOR OF MEDICINE

Preface

Genetics is the foundation of modern biology and medicine, explaining how hereditary information is transmitted, expressed, and altered in living organisms. This glossary presents essential genetics terms in simple two-line definitions, providing a quick and reliable reference for school students, medical and paramedical students, teachers, researchers, and candidates preparing for competitive examinations.

The aim of this preparatio is to simplify complex genetic concepts into clear, concise, and easy-to-understand explanations, making genetics accessible for rapid learning, revision, and everyday reference.

CLINICAL GENETICS -A SHORT INTRODUCTION

PART 01

1. A-DNA
A right-handed double helical form of DNA seen under dehydrated conditions.
It is shorter and wider than B-DNA with about 11 base pairs per turn.

2. ABO BLOOD GROUP
A human blood group system based on A, B, and O alleles determining RBC antigens.
It follows codominance and multiple allele inheritance.

3. ACQUIRED CHARACTER
A trait developed during an organism’s lifetime due to environmental influence.
It is not inherited genetically to the next generation.

4. ADENOMATOUS POLYP
A benign glandular tumor arising in epithelial tissue, especially in the colon.
It is considered a precancerous lesion with malignant potential.

5. AGOUTI
A gene that controls coat color pattern in animals by regulating pigment distribution.
It produces banded hair coloration instead of uniform color.

6. ALBINISM
A genetic disorder characterized by absence of melanin pigment in skin, hair, and eyes.
It is usually inherited as an autosomal recessive trait.

7. ALKAPTON
It is a traditional terms that refers to the  metabolic intermediate related to tyrosine degradation.
Its accumulation is associated with metabolic disorders.

8. ALKAPTONURIA
An inherited metabolic disorder caused by deficiency of homogentisic acid oxidase.
It leads to dark urine and ochronosis.

9. ALLELES OR ALLELOMORPHS
Alternative forms of a gene located at the same locus on homologous chromosomes.
They determine variations of a particular trait.

10. ALLOPOLYPLOID
An organism containing multiple chromosome sets derived from different species.
It results from hybridization followed by chromosome doubling.

11. ALTERNATIVE SPLICING
A process by which a single gene produces multiple mRNA variants.
It increases protein diversity without increasing gene number.

12. AMES ASSAY
A test used to detect mutagenic potential of chemical compounds using bacteria.
It is widely used for screening carcinogens.

13. AMNIOCENTESIS
A prenatal diagnostic procedure involving sampling of amniotic fluid.
It is used to detect genetic abnormalities in the fetus.

14. ANEUPLOID OR HETEROPLOID
A condition where chromosome number is not an exact multiple of haploid set.
Examples include monosomy and trisomy.

15. ANGIOGENESIS
The formation of new blood vessels from pre-existing vessels.
It plays a key role in growth, healing, and tumor development.

16. ANTIBODY
A protein produced by B-lymphocytes in response to antigens.
It specifically binds to and neutralizes foreign substances.

17. ANTICODON
A triplet of nucleotides on tRNA complementary to an mRNA codon.
It ensures correct amino acid incorporation during translation.

18. ANTIGEN
A foreign substance that triggers an immune response in the body.
It is recognized specifically by antibodies or immune cells.

19. ANTI-SENSE RNA
A strand of RNA complementary to messenger RNA.
It regulates gene expression by blocking translation.

20. APOPTOSIS
Programmed cell death characterized by controlled cellular breakdown.
It is essential for development and tissue homeostasis.

21. ARS (AUTOSOMAL RECESSIVE SYNDROME )

A genetic disorder that occurs when an individual inherits two copies of a mutant gene, one from each parent.
Carriers are usually asymptomatic, and the condition typically appears only when both parents transmit the recessive allele.

22. ATAVISM
Reappearance of ancestral traits in an organism.
It occurs due to expression of previously suppressed genes.

23. AUTOPOLYPLOID
An organism with multiple chromosome sets from the same species.
It arises due to duplication of its own genome.

24. AUTORADIOGRAPHY
A technique that uses radioactive isotopes to visualize biological molecules.
It helps in studying DNA, RNA, and protein synthesis.

25. AUTOSOME
Any chromosome that is not involved in sex determination.
Humans have 22 pairs of autosomes.

26. BACK MUTATION
A mutation that restores the original phenotype from a mutant form.
It is also called reverse mutation.

27. BACKCROSS
A cross between a hybrid organism and one of its parents.
Used to study inheritance patterns.

28. BACTERIOPHAGE
A virus that infects and replicates within bacteria.
It is widely used in molecular genetics research.

29. BALANCED LETHAL SYSTEMS
Genetic system where lethal alleles are maintained in heterozygous condition.
Homozygous individuals die, maintaining genetic balance.

30. BARR BODY OR SEX CHROMATIN
An inactivated X chromosome in female somatic cells.
It appears as a dense chromatin mass in the nucleus.

31. BASE PAIRS
Pairs of nitrogenous bases held together by hydrogen bonds in DNA.
A pairs with T, and G pairs with C ensuring genetic stability.

32. BASE–ANALOGUE MUTATION
Mutation caused by incorporation of base analogues during DNA replication.
These analogues mimic normal bases but pair incorrectly.

33. B-DNA
The most common form of DNA under physiological conditions.
It is a right-handed helix with 10 base pairs per turn.

34. BENIGN TUMOR
A non-cancerous growth that does not invade surrounding tissues.
It usually grows slowly and remains localized.

35. BETA-THALASSEMIA
A genetic disorder caused by reduced or absent beta-globin chain synthesis.
It leads to anemia and defective hemoglobin formation.

36. BIDIRECTIONAL REPLICATION
DNA replication proceeding in both directions from the origin.
It increases the speed of DNA synthesis.

37. BIOCHEMICAL GENETICS
Study of genetic control of biochemical pathways in organisms.
It links genes with enzyme functions.

38. BIOENGINEERING
Application of engineering principles to biological systems.
Used in medical devices, tissue engineering, and biotechnology.

39. BIOETHICS
Study of ethical issues arising from biological and medical research.
It deals with topics like cloning, gene therapy, and consent.

40. BIOINFORMATICS
Use of computational tools to analyze biological data.
It is essential for genome sequencing and analysis.

41. BIOLOGIC RESPONSE MODIFIERS
Substances that modify immune system responses(eg cytokines and interferons).
They are used in treatment of cancer and immune disorders.

42. BIOPHYSICS
Application of physical principles to study biological systems.
It explains molecular structure and function.

43. BIOTECHNOLOGY
Use of living organisms to develop useful products.
Includes genetic engineering, fermentation, and cloning.

44. BLOOD TRANSFUSION
Transfer of blood or blood components from donor to recipient.
Compatibility of blood groups is essential to avoid reactions.

45. BLOOM SYNDROME
A genetic disorder characterized by short stature and genomic instability.
It increases susceptibility to cancers.

46. BLUNT-ENDED DNA
DNA fragments with no overhanging ends after cleavage.
They are joined by DNA ligase without base pairing.

47. BURKITT LYMPHOMA
A highly aggressive B-cell cancer associated with chromosomal translocation.
Often linked with Epstein-Barr virus infection.

48. CAGE (CAP ANALYSIS OF GENE EXPRESSION)
A technique to identify transcription start sites in genes.
It analyzes the 5′ end of mRNA.

49. CANCER
A group of diseases involving uncontrolled cell growth and division.
It may invade tissues and spread to other parts of the body.

50. CARCINOGEN
A substance capable of causing cancer.
It induces mutations or promotes tumor formation.

51. CARCINOMA
A malignant tumor arising from epithelial cells.
It is the most common type of cancer.

52. CARRIER
An individual who carries a recessive allele without showing symptoms.
They can transmit the trait to offspring.

53. CASPASES
Proteolytic enzymes involved in apoptosis.
They play a key role in programmed cell death.

54. CDNA (COMPLEMENTARY DNA)
DNA synthesized from mRNA using reverse transcriptase.
It represents expressed genes without introns.

55. CELL CYCLE
The sequence of events leading to cell division.
It includes interphase and mitotic phase.

56. CENTRIOLE
A cylindrical organelle involved in spindle formation during cell division.
Found in animal cells.

57. CENTROMERE
The region of chromosome where sister chromatids are joined.
It is the attachment site for spindle fibers.

58. CENTROSOME
A microtubule-organizing center containing centrioles.
It regulates spindle formation during mitosis.

59. CHANGES IN THE STRUCTURE OF CHROMOSOME
Alterations such as deletion, duplication, inversion, or translocation.
These changes may lead to genetic disorders.

60. CHIASMA TYPE THEORY
Theory explaining crossing over through chiasmata formation.
It occurs during meiosis between homologous chromosomes.

61. CHIMERIC MOLECULE
A molecule composed of genetic material from different sources.
It is commonly produced using recombinant DNA technology.

62. CHIP (CHROMATIN IMMUNOPRECIPITATION)
A technique used to study protein-DNA interactions in cells.
It identifies binding sites of DNA-associated proteins.

63. CHIP-CHIP
A method combining ChIP with microarray analysis.
It is used to detect genome-wide protein-DNA interactions.

64. CHIP-EXO
An advanced ChIP technique with exonuclease trimming.
It provides high-resolution mapping of protein-DNA binding sites.

65. CHIP-SEQ
A method combining ChIP with DNA sequencing.
It identifies protein binding regions across the genome.

66. CHI-SQUARE (Χ²)
A statistical test used to compare observed and expected results.
It is widely used in genetic inheritance studies.

67. CHROMATID
One of the two identical strands of a duplicated chromosome.
They are joined together at the centromere.

68. CHROMATIN REMODELING
Dynamic modification of chromatin structure to regulate gene expression.
It allows access of transcription machinery to DNA.

69. CHROMOSOMAL ABERRATIONS
Structural or numerical changes in chromosomes.
They may lead to genetic disorders or cancer.

70. CHROMOSOMAL INSTABILITY (CIN)
A condition with increased rate of chromosomal changes.
It is commonly seen in cancer cells.

71. CHROMOSOMAL THEORY OF SEX DETERMINATION
Theory stating sex is determined by sex chromosomes (X and Y).
Proposed by Wilson and Stevens based on insect studies.

72. CHROMOSOMAL TRANSLOCATION
Exchange of segments between non-homologous chromosomes.
It may be balanced or unbalanced.

73. CHROMOSOME MAP
A diagram showing the relative positions of genes on a chromosome.
Based on recombination frequencies.

74. CHROMOSOME MAPPING
The process of determining gene locations on chromosomes.
It helps in studying linkage and inheritance.

75. CIRCULAR DNA
DNA molecule forming a closed loop structure.
Commonly found in bacteria and plasmids.

76. CISTRON
A functional unit of DNA coding for a polypeptide.
Equivalent to a gene in classical genetics.

77. CLIP (CROSS-LINKING IMMUNOPRECIPITATION)
A technique to study RNA-protein interactions.
It identifies binding sites on RNA molecules.

78. CLONE
A genetically identical copy of a cell or organism.
Produced through asexual reproduction or cloning techniques.

79. CLONING THE NIF GENE
Transfer of nitrogen fixation gene into another organism.
Used to improve nitrogen-fixing ability in crops.

80. CODOMINANCE
A genetic condition where both alleles express equally.
Example: AB blood group.

81. CODON
A triplet of nucleotides in mRNA coding for an amino acid.
It determines the sequence of proteins.

82. COEFFICIENT OF COINCIDENCE
Ratio of observed to expected double crossovers.
Used to measure interference.

83. COLOUR BLINDNESS
A genetic disorder affecting color perception.
Often X-linked and affects males more frequently.

84. COMPARATIVE GENOMICS
Study of similarities and differences between genomes of organisms.
Helps understand evolution and gene function.

85. COMPLEMENTARY GENES
Genes that interact to produce a phenotype only when both are present.
They follow non-Mendelian inheritance patterns.

86. COMPLETE DOMINANCE
A condition where one allele completely masks the effect of another.
Only the dominant phenotype is expressed.

87. CONJUGATION
Transfer of genetic material between bacteria through direct contact.
Mediated by sex pili.

88. CONTINUOUS VARIATION
Variation showing a range of phenotypes without distinct categories.
Controlled by multiple genes and environment.

89. COPY NUMBER VARIATION (CNV)
Variation in the number of copies of a DNA segment.
It contributes to genetic diversity and disease.

90. COSMID
A hybrid vector combining plasmid and phage DNA.
Used for cloning large DNA fragments. 

91. COUPLING
The inheritance of linked genes together on the same chromosome.
It reduces recombination between closely located genes.

92. CRIS-CROSS OR ZIG-ZAG INHERITANCE
Pattern of inheritance where traits pass from father to daughter to grandson.
Commonly seen in X-linked traits.

93. CRISPR/CAS
A gene-editing system derived from bacterial immune defense.
It allows precise modification of DNA sequences.

94. CROSSING OVER
Exchange of genetic material between homologous chromosomes during meiosis.
It increases genetic variation.

95. CYTOPLASMIC INHERITANCE
Transmission of traits through cytoplasmic organelles like mitochondria.
It is usually maternally inherited.

96. DEFICIENCY
Loss of a segment of a chromosome.
It may lead to genetic disorders.

97. DEGENERATE CODE
Property of genetic code where multiple codons code for the same amino acid.
It provides protection against mutations.

98. DELETION
Removal of a DNA segment from a chromosome.
It may cause severe genetic effects.

99. DEOXYRIBONUCLEIC ACID (DNA)
The hereditary material carrying genetic information in cells.
It consists of double-stranded helix of nucleotides.

100. DIFFERENCES BETWEEN GENOTYPE AND PHENOTYPE
Genotype refers to genetic makeup of an organism.
Phenotype refers to observable characteristics influenced by genes and environment.

END OF PART 01

  CLINICAL GENETICS

A SHORT INTRODUCTION

BY

DR.C.GANESAN M.D.,

PROFESSOR OF MEDICINE

Preface

Genetics is the foundation of modern biology and medicine, explaining how hereditary information is transmitted, expressed, and altered in living organisms. This glossary presents essential genetics terms in simple two-line definitions, providing a quick and reliable reference for school students, medical and paramedical students, teachers, researchers, and candidates preparing for competitive examinations.

The aim of this preparatio is to simplify complex genetic concepts into clear, concise, and easy-to-understand explanations, making genetics accessible for rapid learning, revision, and everyday reference. 

CLINICAL GENETICS -A SHORT INTRODUCTION

PART 03

201. INDEPENDENT ASSORTMENT
Law stating genes segregate independently during gamete formation.
Applies to genes on different chromosomes.

202. INDUCED MUTATION
Mutation caused by external agents like radiation or chemicals.
It increases mutation rate.

203. INSERT
A DNA fragment inserted into a vector during cloning.
Used in recombinant DNA technology.

204. INTERFERENCE
Phenomenon where one crossover affects occurrence of another.
It reduces double crossing over.

205. INTERMEDIATE LETHAL GENES
Genes causing death only under certain conditions.
They show partial lethality.

206. INTERSEX
Individuals with characteristics of both sexes.
Caused by hormonal or chromosomal abnormalities.

207. INTRON
Non-coding sequence removed during RNA processing.
It is not translated into protein.

208. IONIZING RADIATION
Radiation capable of removing electrons from atoms.
It can cause DNA damage and mutations.

209. ISOZYMES
Different forms of an enzyme with similar function.
They vary in structure and regulation.

210. KAPPA PARTICLES
Cytoplasmic elements found in Paramecium.
They are associated with killer trait. 

211. KAPPA PARTICLES IN PARAMECIUM
Endosymbiotic particles in Paramecium responsible for killer trait.
They produce toxins harmful to sensitive strains.

212. KARYOTYPE
The complete set of chromosomes arranged in pairs.
Used to detect chromosomal abnormalities.

213. KINETOCHORE
A protein structure on centromere where spindle fibers attach.
It is essential for chromosome movement during cell division.

214. KLINEFELTER’S SYNDROME
A chromosomal disorder with XXY karyotype in males.
It causes infertility and secondary sexual changes.

215. LAMP BRUSH CHROMOSOMES
Large chromosomes with extended loops seen in oocytes.
They are active in transcription.

216. LAW OF INDEPENDENT ASSORTMENT
Genes for different traits assort independently during gamete formation.
Applies when genes are unlinked.

217. LAW OF INDEPENDENT ASSORTMENT AND DIHYBRID EXPERIMENT
Mendel’s dihybrid cross demonstrating independent assortment.
Results in 9:3:3:1 phenotypic ratio.

218. LAW OF SEGREGATION
Alleles separate during gamete formation.
Each gamete carries one allele.

219. LEAKY MUTATION
Mutation with partial gene function retained.
It results in reduced but not absent activity.

220. LETHAL GENES
Genes that cause death when present in certain genotypes.
Often recessive in nature.

221. LETHAL MUTATION (GENE)
A mutation leading to organismal death.
It disrupts essential functions.

222. LEUKEMIAS
Cancers of blood-forming tissues.
Characterized by abnormal proliferation of white blood cells.

223. LIBRARY
Collection of cloned DNA fragments.
Includes genomic and cDNA libraries.

224. LIGATION
Joining of DNA fragments using DNA ligase enzyme.
Essential step in recombinant DNA technology.

225. LINEAR ARRANGEMENT
Genes are arranged linearly on chromosomes.
Supports chromosome theory of inheritance.

226. LINES OF PURITY OR PURE LINES

Pure lines are genetically identical individuals produced by repeated self-fertilization or inbreeding.
They show uniform traits and are homozygous for most genes across generations.

227. LINKAGE
Tendency of genes on same chromosome to be inherited together.
Reduces independent assortment.

228. LINKAGE GROUP
Group of genes located on the same chromosome.
Inherited together as a unit.

229. LIPIDOMICS
Study of lipid profiles in cells and tissues.
Helps understand metabolic and disease processes.

230. LOCUS
Specific position of a gene on a chromosome.
Each gene occupies a fixed locus.

231. LOSS OF HETEROZYGOSITY (LOH)
Loss of one allele in a heterozygous cell.
Common in cancer development.

232. LYMPHOMA
Cancer of lymphatic system cells.
Includes Hodgkin and non-Hodgkin types.

233. LYSIS
Breakdown or rupture of a cell.
Often caused by viral infection.

234. LYSOGENIC
A viral state where genome integrates into host DNA.
No immediate destruction of host cell.

235. LYSOGENIC CYCLE
Viral replication cycle involving integration into host genome.
Can switch to lytic cycle.

236. LYTIC CYCLE
Viral replication leading to host cell destruction.
Produces many new virus particles.

237. MALIGNANT CELLS
Cancerous cells that invade and spread.
They show uncontrolled growth.

238. MATERNAL INHERITANCE
Transmission of traits through maternal cytoplasm.
Often involves mitochondrial DNA.

239. MENDEL
Gregor Mendel, father of genetics.
He discovered basic laws of inheritance.

240. MENDEL’S LAWS
Fundamental principles of inheritance.
Include segregation and independent assortment.

241. MENDELIAN POPULATION
A population where individuals interbreed freely.
Allele frequencies are studied in such populations.

242. MENDELISM
Study of inheritance patterns based on Mendel’s principles.
It explains transmission of traits.

243. MESSENGER RNA (mRNA)
RNA molecule that carries genetic information from DNA to ribosome.
It serves as template for protein synthesis.

244. METABOLOMICS
Study of small molecule metabolites in biological systems.
It reflects cellular metabolic state.

245. METASTASIS
Spread of cancer cells from primary site to distant organs.
It is a hallmark of malignant tumors.

246. MICROBIAL GENETICS
Study of genetics in microorganisms.
Includes bacteria, viruses, and fungi.

247. MICROSATELLITE INSTABILITY
Condition of increased mutation in repetitive DNA sequences.
Associated with certain cancers.

248. MICROSATELLITE POLYMORPHISM
Variation in length of microsatellite sequences.
Used in genetic mapping and DNA profiling.

249. MICROSATELLITE REPEAT SEQUENCES
Short tandem repeats of DNA sequences.
Highly variable among individuals.

250. MIGRATION AND GENE FLOW
Movement of individuals causing transfer of genes between populations.
It alters allele frequencies.

251. MIRNAS
Small non-coding RNAs that regulate gene expression.
They inhibit translation or degrade mRNA.

252. MODIFYING GENE
Gene that alters expression of another gene.
It influences phenotype without direct effect.

253. MOLECULAR DIAGNOSTICS
Techniques used to detect genetic disorders at molecular level.
Includes PCR and sequencing methods.

254. MONOSOMY
Condition where one chromosome is missing.
Example: Turner syndrome (45,X).

255. MONOZYGOTIC TWINS
Twins arising from a single fertilized egg.
They are genetically identical.

256. MULATTO

(The better term is ADMIXXED POPULATION)
Term referring to offspring of mixed ancestry.
Used historically in genetics context.

257. MULTIGENIC INHERITANCE
Traits controlled by multiple genes.
Results in continuous variation.

258. MULTIPLE ALLELES
More than two alleles for a gene in a population.
Example: ABO blood group.

259. MULTIPLE CROSSING OVER
More than two crossing over events between chromosomes.
It increases recombination complexity.

260. MULTIPLE GENE INHERITANCE
Inheritance involving several genes affecting one trait.
Also called polygenic inheritance.

261. MULTIPLE GENES
Several genes contributing to a single phenotype.
They show additive effects.

262. MUTATION
A permanent change in DNA sequence.
It may be spontaneous or induced.

263. MUTON
Smallest unit of mutation within a gene.
Represents a single nucleotide change.

264. NANOTECHNOLOGY
Application of nanoscale materials in science and medicine.
Used in drug delivery and diagnostics.

265. NATURAL SELECTION
Process where favorable traits increase survival and reproduction.
It drives evolution.

266. NECROSIS
Uncontrolled cell death due to injury or damage.
It often causes inflammation.

267. NEOPLASM
An abnormal mass of tissue due to uncontrolled growth.
It may be benign or malignant.

268. NICK TRANSLATION
Technique where DNA polymerase replaces nucleotides at nicked sites.
Used for labeling DNA.

269. NITROGENOUS BASES
Organic bases in nucleic acids: A, T, G, C, and U.
They form the genetic code.

270. NON-DISJUNCTION
Failure of chromosomes to separate during cell division.
It leads to aneuploidy.

271. NONSENSE CODONS
Codons that do not code for any amino acid.
They signal termination of protein synthesis.

272. NONSENSE MUTATION
A mutation converting a codon into a stop codon.
It results in premature termination of protein.

273. NORTHERN BLOT
Technique used to detect RNA sequences.
It involves hybridization with labeled probes.

274. NUCLEASE
Enzyme that cleaves nucleic acids.
Includes endonucleases and exonucleases.

275. NUCLEIC ACIDS
Macromolecules that store genetic information.
Includes DNA and RNA.

276. NUCLEOSIDES
Molecules consisting of base and sugar without phosphate.
They are components of nucleotides.

277. NUCLEOTIDES
Basic units of nucleic acids composed of base, sugar, and phosphate.
They form DNA and RNA chains.

278. NULLISOMY
Condition where a pair of chromosomes is missing.
It is usually lethal.

279. NUTRIGENOMICS
Study of interaction between nutrition and genes.
It influences health and disease.

280. OLIGONUCLEOTIDE
Short sequence of nucleotides.
Used as primers or probes in molecular biology.

281. ONCOGENE
A mutated gene that promotes cancer development.
Derived from proto-oncogenes.

282. ONCOLOGY
Study of cancer and tumors.
Includes diagnosis and treatment.

283. ONE GENE ONE ENZYME HYPOTHESIS
Concept stating each gene codes for a specific enzyme.
Proposed by Beadle and Tatum.

284. OPERATOR GENE
DNA segment controlling gene expression in operon.
It interacts with regulatory proteins.

285. OPERON HYPOTHESIS
Model explaining gene regulation in prokaryotes.
Includes promoter, operator, and structural genes.

286. ORIGIN OF REPLICATION (ORI)
Specific DNA sequence where replication begins.
Essential for DNA duplication.

287. OUTBREEDING
Mating between unrelated individuals.
It increases genetic diversity.

288. PAC (P1-DERIVED ARTIFICIAL CHROMOSOME)
Cloning vector capable of carrying large DNA fragments.
Used in genomic studies.

289. PALINDROME
DNA sequence reading the same in both directions.
Important in restriction enzyme recognition.

290. PALINDROMIC DNA
DNA with inverted repeat sequences.
Forms secondary structures.

291. PANGENESIS
Theory suggesting all body parts produce particles for inheritance.
Proposed by Darwin.

292. PANGENIC THEORY
Concept similar to pangenesis explaining heredity.
It is now obsolete.

293. PARTHENOGENESIS
Development of organism from unfertilized egg.
Common in some insects.

294. PARTICULATE THEORY
Theory stating inheritance is through discrete particles (genes).
Proposed by Mendel.

295. PEDIGREE ANALYSIS
Study of inheritance patterns using family trees.
Helps trace genetic disorders.

296. PENETRANCE
Proportion of individuals showing a particular genotype expression.
It may be complete or incomplete.

297. PHARMACOGENOMICS
Study of how genes affect drug response.
It helps in personalized medicine.

298. PHENYLKETONURIA (PKU)
Genetic disorder due to phenylalanine metabolism defect.
Leads to mental retardation if untreated.

299. PHILADELPHIA CHROMOSOME
Abnormal chromosome formed by translocation.
Associated with chronic myeloid leukemia.

300. PHOSPHORIC ACID (H₃PO₄)
Component of nucleotides forming phosphate backbone.
It links nucleotides in DNA.

END OF PART 03

 

CLINICAL GENETICS

A SHORT INTRODUCTION

BY

DR.C.GANESAN M.D.,

PROFESSOR OF MEDICINE

Preface

Genetics is the foundation of modern biology and medicine, explaining how hereditary information is transmitted, expressed, and altered in living organisms. This glossary presents essential genetics terms in simple two-line definitions, providing a quick and reliable reference for school students, medical and paramedical students, teachers, researchers, and candidates preparing for competitive examinations.

The aim of this preparatio is to simplify complex genetic concepts into clear, concise, and easy-to-understand explanations, making genetics accessible for rapid learning, revision, and everyday reference.

CLINICAL GENETICS -A SHORT INTRODUCTION

PART 04

301. PLASMA GENE
Gene located outside nucleus, usually in mitochondria or chloroplasts.
It shows maternal inheritance.

302. PLASMID
A small circular DNA molecule found in bacteria.
It replicates independently of chromosomal DNA.

303. PLASTID INHERITANCE IN MIRABILIS
Cytoplasmic inheritance of leaf color in Mirabilis jalapa.
It depends on plastids transmitted from mother.

304. PLEIOTROPISM
A single gene affecting multiple traits.
It shows multiple phenotypic effects.

305. POINT MUTATION
A mutation involving change in a single nucleotide.
It may alter protein function.

306. POLIGREE
A group of related individuals used in genetic studies.
Similar to pedigree analysis.

307. POLYGENES
Multiple genes controlling a single trait.
They contribute additively.

308. POLYPLOIDY
Condition of having more than two sets of chromosomes.
Common in plants.

309. POLYMERASE CHAIN REACTION (PCR)
Technique used to amplify DNA sequences.
It produces millions of copies of DNA.

310. POPULATION GENETICS
Study of genetic variation in populations.
It analyzes allele frequencies.

311. POSITION EFFECT
Change in gene expression due to its position.
Occurs after chromosomal rearrangement.

312. POSITIVE EUGENICS
Encouragement of reproduction among desirable individuals.
Aimed at improving genetic traits.

313. PRIMOSOME
Protein complex initiating DNA replication.
It synthesizes RNA primers.

314. PROBE
A labeled DNA or RNA sequence used to detect complementary sequences.
Used in hybridization techniques.

315. PROCARCINOGEN
An inactive substance that becomes carcinogenic after activation.
Converted by metabolic processes.

316. PROMOTER SEQUENCES
DNA regions where RNA polymerase binds.
They initiate transcription.

317. PRO-SEQ (PRECISION RUN-ON SEQUENCING)
Technique to study transcription at high resolution.
Measures actively transcribing RNA polymerases.

318. PROTEIN SYNTHESIS
Process of forming proteins from amino acids.
Includes transcription and translation.

319. PROTEOME
Complete set of proteins expressed by a genome.
Varies with cell type and condition.

320. PROTEOMICS
Study of structure and function of proteins.
It analyzes protein interactions and expression.

321. PROTO-ONCOGENE
Normal gene involved in cell growth regulation.
Mutation converts it into oncogene.

322. PSEUDOALLELES
Closely linked genes with similar function.
They behave like alleles.

323. PSEUDOGENE
A non-functional gene resembling a functional gene.
It arises due to mutation.

324. PTC (PHENYL THIOCARBAMIDE)
A chemical used to study taste sensitivity.
Ability to taste it is genetically determined.

325. PURE LINE
A genetically uniform line produced by selfing.
Used in genetic experiments.

326. QUANTITATIVE INHERITANCE
Inheritance of traits showing continuous variation.
Controlled by multiple genes.

327. QUANTITATIVE THEORY OF SEX DETERMINATION
Sex determined by ratio of X chromosomes to autosomes.
Supported by Drosophila studies.

328. RADIATION AND BOMBS
High-energy radiation causing genetic mutations.
Includes X-rays and nuclear radiation.

329. RADIATION GENETICS
Study of effects of radiation on genes.
It induces mutations.

330. RECESSIVENESS
Condition where allele expresses only in homozygous state.
Masked by dominant allele.

331. RECIPROCAL CROSSES
Crosses with reversed parental sexes.
Used to study sex-linked inheritance.

332. RECOMBINANT DNA
DNA formed by combining sequences from different sources.
Used in genetic engineering.

333. RECOMBINATION
Exchange of genetic material between chromosomes.
Increases genetic diversity.

334. RED GREEN COLOUR BLINDNESS
An X-linked disorder affecting color vision.
Common in males.

335. REGULATION
Control of gene expression in cells.
Ensures proper functioning.

336. REGULATION OF GENE EXPRESSION
Mechanisms controlling when and how genes are expressed.
Includes transcriptional and post-transcriptional control.

337. REGULATION OF TRANSCRIPTION
Control of RNA synthesis from DNA.
Involves promoters and transcription factors.

338. RELAXED DNA
DNA in less coiled state.
It is transcriptionally active.

339. REPLICATION OF DNA
Process of copying DNA before cell division.
It is semi-conservative.

340. REPLICATION SLIPPAGE
Error during DNA replication causing repeat expansion.
Leads to mutations.

341. RESTRICTION ENDONUCLEASES
Enzymes cutting DNA at specific sequences.
Used in molecular biology.

342. RESTRICTION ENZYME
Enzyme that cleaves DNA at recognition sites.
Important in cloning.

343. RETINOBLASTOMA
A childhood eye tumor caused by gene mutation.
Involves tumor suppressor gene.

344. REVERSE TRANSCRIPTION
Synthesis of DNA from RNA template.
Carried out by reverse transcriptase.

345. RH BLOOD GROUP
Blood group system based on Rh antigen.
Important in transfusion and pregnancy.

346. RIBOSOMAL RNA (rRNA)
RNA component of ribosomes.
Plays role in protein synthesis.

347. RIBOSOME PROFILING
Technique to study translation by sequencing ribosome-bound mRNA.
Gives insight into protein synthesis.

348. RIP (RNA IMMUNOPRECIPITATION)
Technique to study RNA-protein interactions.
Identifies RNA bound to proteins.

349. ROUS SARCOMA VIRUS (RSV)
A virus causing sarcoma in chickens.
First virus linked to cancer.

350. RT-PCR
Technique combining reverse transcription and PCR.
Used to detect RNA expression.

351. SARCOMA
A malignant tumor arising from connective tissues.
Includes bone and muscle cancers.

352. SEQUENCING AND ANALYSIS
Determining nucleotide order in DNA.
Used in genomics research.

353. SEX CHROMOSOME
Chromosomes determining sex of an organism.
Example: X and Y in humans.

354. SEX DETERMINATION
Mechanism deciding sex of an organism.
Based on genetic or environmental factors.

355. SEX DETERMINATION BY BARR BODY
Sex identification based on presence of Barr body.
Indicates inactive X chromosome.

356. SEX INFLUENCED GENES
Genes expressed differently in males and females.
Influenced by hormonal environment.

357. SEX LIMITED GENES
Genes expressed only in one sex.
Example: milk production in females.

358. SEX LINKAGE
Inheritance of genes located on sex chromosomes.
Shows distinct patterns.

359. SEX LINKED INHERITANCE
Transmission of traits via X or Y chromosome.
Often affects males more.

360. SEX LINKED LETHALS
Lethal genes located on sex chromosomes.
Often expressed in males.

361. SEX MOSAICS
Individuals with cells of different sex chromosome composition.
Result from non-disjunction.

362. SEX REVERSAL
Condition where genetic sex differs from phenotypic sex.
Caused by hormonal or genetic factors.

363. SEXDUCTION
Transfer of bacterial genes via F-factor.
A form of conjugation.

364. SIAMESE TWINS
Conjoined twins resulting from incomplete separation of monozygotic twins.
They share body structures and organs.

365. SIAMESE TWINS SIMILARITY.
They are similar to monozygotic twins.
Arise from a single zygote.

366. SICKLE CELL ANAEMIA
Genetic disorder caused by hemoglobin mutation.
Leads to sickle-shaped RBCs.

367. SIGNAL
A molecular message triggering cellular response.
Involved in communication pathways.

368. SIMPLE MENDELIAN TRAITS IN MAN
Traits inherited according to Mendelian laws.
Example: widow’s peak.

369. SINES X
Short interspersed nuclear elements on X chromosome.
They are repetitive DNA sequences.

370. SINGLE CROSSING OVER
One exchange between homologous chromosomes.
Produces recombinant chromatids.

371. SINGLE STRANDED DNA
DNA consisting of a single nucleotide chain.
Seen in some viruses.

372. SIRNAS
Small interfering RNAs that silence gene expression.
They degrade target mRNA.

373. SIZE OF A GENE
Length of DNA segment coding for a gene.
Varies widely among genes.

374. SNP (SINGLE NUCLEOTIDE POLYMORPHISM)
Variation at a single nucleotide position.
Common genetic marker.

375. SNRNA (SMALL NUCLEAR RNA)
RNA involved in splicing of pre-mRNA.
Forms spliceosome.

376. SOUTHERN BLOT
Technique used to detect DNA sequences.
Involves hybridization with probes.

377. SOUTHWESTERN BLOT
Technique to study DNA-protein interactions.
Combines Southern and Western methods.

378. SPLICEOSOME
Complex of RNA and proteins for RNA splicing.
Removes introns.

379. SPLICING
Removal of introns from pre-mRNA.
Produces mature mRNA.

380. SPONTANEOUS MUTATION
Mutation occurring naturally without external cause.
Due to replication errors.

381. STEM CELL BIOLOGY
Study of undifferentiated cells capable of division.
They can differentiate into various cell types.

382. STICKY-ENDED DNA
DNA fragments with overhanging ends.
Facilitates recombination.

383. STRAIN OR TORSION THEORY
Theory explaining crossing over by torsional stress.
Suggests mechanical forces involved.

384. STRUCTURE OF RNA
RNA has primary, secondary (hairpin), and tertiary structures.
It is usually single-stranded with functional folding.

385. SUGAR
Pentose sugar in nucleotides (ribose or deoxyribose).
Forms backbone of nucleic acids.

386. SUPER SEXES
Individuals with abnormal number of sex chromosomes.
Example: XXX or XYY.

387. SUPPLEMENTARY GENES
Genes that interact to produce a phenotype.
One gene enhances effect of another.

388. SYNDROMES
Group of symptoms occurring together.
Often associated with genetic disorders.

389. SYNTHETIC BIOLOGY
Design and construction of new biological systems.
Combines biology and engineering.

390. SYSTEMS BIOLOGY
Study of complex interactions in biological systems.
Uses computational modeling.

391. T4 BACTERIOPHAGE
A virus infecting E. coli.
Used in genetic research.

392. TANDEM
Repeated sequences arranged one after another.
Common in DNA repeats.

393. TELOMERES
Protective ends of chromosomes.
They prevent degradation.

394. TEMPERATURE SENSITIVE MUTATION
Mutation expressed only at certain temperatures.
Used in experimental genetics.

395. TERMINAL TRANSFERASE
Enzyme adding nucleotides at DNA ends.
Used in molecular biology.

396. TEST CROSS
Cross between unknown genotype and recessive homozygote.
Used to determine genotype.

397. THEORY OF EPIGENESIS
Concept that development occurs through gradual differentiation.
Opposes preformation theory.

398. THEORY OF HETEROGAMESIS
Theory explaining sex determination by different gametes.
Example: XY males.

399. TRANSCRIPTION
Synthesis of RNA from DNA template.
First step of gene expression.

400. TRANSCRIPTOME
Complete set of RNA transcripts in a cell.
Varies with conditions.

401. TRANSCRIPTOMICS
Study of transcriptome using high-throughput methods.
Analyzes gene expression.

402. TRANSDUCTION
Transfer of DNA by bacteriophages.
Used in bacterial genetics.

403. TRANSFER RNA (tRNA)
RNA carrying amino acids to ribosome.
Contains anticodon.

404. TRANSFORMATION
Uptake of foreign DNA by a cell.
Leads to genetic change.

405. TRANSGENIC
Organism containing foreign genes.
Produced by genetic engineering.

406. TRANSGRESSIVE VARIATION
Offspring showing traits beyond parental range.
Due to gene interaction.

407. TRANSITION
Mutation replacing purine with purine or pyrimidine with pyrimidine.
It is a point mutation.

408. TRANSLATION
Process of protein synthesis from mRNA.
Occurs at ribosome.

409. TRANSLOCATION
Exchange of chromosome segments between non-homologous chromosomes.
May cause disorders.

410. TRANSVERSION
Mutation replacing purine with pyrimidine or vice versa.
It alters DNA structure.

411. TRISOMY
Presence of an extra chromosome.
Example: Down syndrome.

412. TRISOMY OF NON–DISJUNCTION
Failure of chromosomes to separate leads to trisomy.
Results in abnormal chromosome number.

413. TUMOR
Abnormal mass of cells due to uncontrolled growth.
May be benign or malignant.

414. TUMOR SUPPRESSOR GENE
Gene that prevents uncontrolled cell division.
Loss leads to cancer.

415. TURNER’S SYNDROME
A chromosomal disorder with single X chromosome (45,X).
Causes female infertility.

416. TWINS
Two offspring born from same pregnancy.
May be monozygotic or dizygotic.

417. TYPE OF SEX LINKED INHERITANCE
Patterns include X-linked and Y-linked inheritance.
They show distinct transmission.

418. TYPES OF DNA
Forms include A-DNA, B-DNA, and Z-DNA.
They differ in structure.

419. VECTOR
DNA molecule used to carry foreign DNA into host cell.
Examples include plasmids.

420. WATSON AND CRICK MODEL OF DNA
Double helix model explaining DNA structure.
It shows base pairing and replication mechanism.

421. WESTERN BLOT
Technique to detect proteins using antibodies.
It identifies specific proteins.

422. WIENER’S THEORY
Theory explaining Rh blood group inheritance.
Based on multiple alleles.

423. X-LINKED INHERITANCE
Inheritance of genes located on X chromosome.
Affects males more frequently.

424. X-RAY
High-energy radiation used in medical imaging.
It can induce mutations.

425. Y-LINKED INHERITANCE
Inheritance of genes on Y chromosome.
Passed from father to son.

426. Z-DNA
Left-handed helical form of DNA.
Occurs under specific conditions.

END OF PART 04