The basic DNA unit.
A, T, C, G.
Sequence order carries genetic information.
Side 62
Genetics
A study of biological information across generations. Genetics connects DNA sequence, gene expression, variation, inheritance and recombination to phenotype and population change.
DNA→gene→variation→inheritance→phenotype
06genetic lenses
04inheritance patterns
05variation mechanisms
62Side
Genes are encoded in DNA sequence.
Sequence provides a durable information substrate, but function depends on regulation, context and interaction.
A functional genomic region.
Product + regulation.
Genes include more than protein-coding sequence alone.
DNA packaged at larger scale.
Genome organization.
Genes occupy physical positions and can be inherited together when linked.
A sequence variant at a locus.
Alternative version.
Alleles can differ in function, regulation or have little measurable effect.
The inherited variant combination.
At one or many loci.
Genotype contributes to phenotype through development and environment.
Genetic information must be expressed to affect cell behavior.
Regulation determines when, where and how strongly genes contribute to cellular function.
DNA → RNA.
RNA polymerase copies selected DNA regions into RNA.
Modify the transcript.
Splicing and other processing steps can change the final RNA product.
RNA → protein.
Ribosomes decode messenger RNA into amino-acid sequence.
Control expression level.
Promoters, enhancers and regulatory proteins shape transcription.
Chromatin affects accessibility.
DNA and histone modifications can alter gene expression without changing sequence.
Same genome, different cells.
Cell types differ because they express different subsets of genes.
Inheritance patterns emerge from chromosome behavior and gene interaction.
Mendelian ratios are powerful starting models, not descriptions of every trait.
| Pattern | Core idea | Typical clue | Caution |
|---|---|---|---|
| Dominant / recessive | Heterozygote resembles one homozygote | Characteristic pedigree ratios | Dominance describes phenotype, not allele “strength” |
| Incomplete dominance | Heterozygote intermediate | Three distinguishable genotypes | Depends on trait measurement |
| Codominance | Both alleles visibly contribute | Both products detectable | Not the same as blending |
| Sex-linked | Locus on sex chromosome | Transmission differs by sex chromosomes | Patterns depend on species system |
| Polygenic | Many loci contribute | Continuous variation | Environment often contributes strongly too |
Variation is generated, shuffled and filtered.
Mutation creates new sequence variants; recombination and segregation rearrange existing variation.
Single-base change.
Can be neutral, regulatory, synonymous or alter protein sequence.
Add or remove sequence.
Effects depend on size and genomic location.
Duplicate or delete larger regions.
Gene dosage can alter phenotype.
Move or invert chromosomal segments.
Can disrupt genes or change regulatory context.
Variant absent from parents.
Novel germline variants enter pedigrees and populations.
Existing diversity in a population.
Selection often acts on variants already present.
Meiosis reshuffles inherited information.
Segregation and crossing over create gametes with new combinations of parental alleles.
Pairing
Homologous chromosomes align.
Maternal and paternal homologs pair during meiosis.
Crossing over
Exchange between homologs.
Recombination breaks up inherited haplotypes.
Segregation
Alleles separate into gametes.
Each gamete receives one member of each homologous pair.
Independent assortment
Different chromosome pairs segregate independently.
Genes close together on one chromosome can violate simple independence.
Linkage
Nearby loci tend to travel together.
Recombination frequency can reveal relative genetic distance.
Population genetics tracks allele frequencies through time.
Mutation, selection, drift, migration and mating structure alter genetic composition.
Mutation
Introduces new variants into the population.
Selection
Changes allele frequencies through differential reproductive success.
Drift
Random sampling changes frequencies, especially in small populations.
Gene flow
Migration moves alleles among populations.
Assortative mating
Nonrandom mating changes genotype frequencies and can reshape trait distributions.
Introduction to Genetic AnalysisGriffiths et al. · genetics foundation
Genetics: Analysis and PrinciplesBrooker · inheritance and molecular genetics
Principles of Population GeneticsHartl & Clark · population change
Molecular Biology of the CellAlberts et al. · gene expression context