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