Mendelian genetics, alleles, linkage, molecular mutations, mobile elements, HGT.
Classical And Molecular Genetics
Gene
Unit of heredity: a locus on chromosome whose variants (alleles) affect phenotype. Molecular definition: DNA segment encoding a functional…
Allele
Alternative sequence variant of a gene at a given locus. Diploid organism has two alleles per autosomal locus; may be homozygous…
Mendel's laws
Segregation: alleles separate in gamete formation (one per gamete). Independent assortment: alleles of different genes segregate…
Genetic linkage
Co-segregation of loci on the same chromosome at higher-than-Mendelian frequencies. Recombination frequency (cM, Morgan unit) measures…
Mutation
Heritable change in DNA sequence. Point (substitution, insertion, deletion), structural (inversion, translocation, CNV), or aneuploidy.…
Point mutation
Single-nucleotide change: missense (AA change), nonsense (stop codon), silent (synonymous), or frameshift (indel not-divisible-by-3 in…
Transposable element (transposon)
Mobile DNA sequence that moves within genome via DNA (cut-and-paste, Tc1/mariner) or RNA (copy-and-paste, retroelement) intermediates. ~50%…
Horizontal gene transfer (HGT)
Acquisition of genetic material between non-parent-offspring organisms (conjugation, transformation, transduction in prokaryotes;…
Chromosomal aberration
Structural (deletion, duplication, inversion, translocation) or numerical (aneuploidy, polyploidy). Down syndrome (trisomy 21),…
Gene conversion
Non-reciprocal transfer of sequence during recombination, converting one allele to another. Drives concerted evolution of gene families…
Complementation-test framework
Cross-mutant test for allelism: two recessive mutants are crossed; if the F₁ heterozygote shows wild-type phenotype, the mutations…
LOD-score linkage-mapping framework
Morton 1955 logarithm-of-odds: LOD = log₁₀[L(θ)/L(0.5)] where L(θ) is the likelihood of recombination fraction θ between two loci. LOD ≥ 3…
Watson-Crick base pairing
Watson-Crick 1953 Nobel 1962: A pairs with T (DNA) or U (RNA) via 2 H-bonds; G pairs with C via 3 H-bonds; antiparallel double helix;…
Drosophila (Morgan 1910)
T H Morgan 1910 (Nobel 1933) sex-linkage white-eye; modern Drosophila as genetic-model + balancer-chromosomes.
DNA-as-genetic-material (Avery 1944)
Avery-MacLeod-McCarty 1944 transformation; DNA = genetic material; foundational pre-Watson-Crick experiment.
Hershey-Chase (1952)
Hershey-Chase 1952 phage labeling 35S vs 32P confirms DNA-genetic-material; (Hershey Nobel 1969).
Fine structure (Benzer 1955)
S Benzer 1955 rII fine-structure mapping; modern recombination-based mapping resolution to single-nt.
Complementation (Fincham 1957)
J Fincham 1957 complementation-test; modern allelism-vs-non-allelism distinction; cis-trans test.
Conjugation (Tatum-Lederberg 1946)
Tatum-Lederberg 1946 (Nobel 1958) bacterial-conjugation; modern F-plasmid + transposon + horizontal-gene-transfer.
Transduction (Zinder-Lederberg 1952)
Zinder-Lederberg 1952 phage transduction; modern P22-Salmonella + lambda-E.coli + generalized vs specialized.
Transformation (Griffith 1928)
F Griffith 1928 pneumococcus-transformation; foundational to Avery-MacLeod-McCarty 1944; modern bacterial competence.
Operon induction (Jacob-Monod 1961)
Jacob-Monod 1961 (Nobel 1965) lac-operon; modern arabinose + tryptophan + phage-lambda CI bistable switch.
Rec (Clark 1965)
A J Clark 1965 RecA-RecB-RecC mutants E coli; modern Rad51 eukaryote homolog + DNA-repair foundation.
Gene mapping (Sturtevant 1913)
A Sturtevant 1913 first-ever gene-map Drosophila X-chromosome; modern centiMorgan + LOD-score linkage analysis.