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