Genetics Calculators

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Genetics is the science of heredity and genetic variation — how traits are passed from parents to offspring and how genetic information is encoded, expressed, and modified. It spans from classical Mendelian genetics (segregation, independent assortment, dominance) to molecular genetics (gene structure, transcription, translation, mutation) and population genetics (allele frequencies, Hardy-Weinberg equilibrium, natural selection, genetic drift). Genetics underpins medicine (hereditary diseases, pharmacogenomics), agriculture (plant and animal breeding), evolutionary biology, and forensic science.

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Mendelian Genetics

Gregor Mendel's two laws: Law of Segregation: the two alleles of a gene separate during gamete formation; each gamete receives one allele. Law of Independent Assortment: alleles for different genes assort independently into gametes (when on different chromosomes). Dominant allele masks recessive allele in the heterozygote. Monohybrid cross (Aa × Aa): 1 AA : 2 Aa : 1 aa (genotype); 3 dominant : 1 recessive (phenotype). Dihybrid cross (AaBb × AaBb): 9:3:3:1 phenotype ratio.

Genotype vs. Phenotype

Genotype: the genetic constitution of an organism (e.g., Aa). Phenotype: the observable trait (e.g., brown eyes). Phenotype = genotype × environment. Penetrance: the proportion of individuals with a genotype who express the associated phenotype. Expressivity: the degree to which a phenotype is expressed.

Hardy-Weinberg Equilibrium

In a large, randomly mating population with no selection, mutation, migration, or drift: p + q = 1 (allele frequencies); p² + 2pq + q² = 1 (genotype frequencies), where p = frequency of dominant allele A; q = frequency of recessive allele a. Deviations from HWE indicate evolutionary forces acting.

Molecular Genetics

Gene: a segment of DNA encoding a functional RNA or protein. Alleles: alternative forms of a gene at the same locus. Mutation: heritable change in DNA sequence. Types: point mutations (substitution, insertion, deletion), frameshift, nonsense, missense, splice-site. Epigenetics: heritable changes in gene expression without DNA sequence change (methylation, histone modification).

Glossary

Genetics
The science of heredity and genetic variation; encompasses Mendelian inheritance, molecular genetics, population genetics, and genomics.
Hardy-Weinberg Equilibrium
p² + 2pq + q² = 1; predicts genotype frequencies in a non-evolving population; requires large size, random mating, no selection/mutation/migration; deviations indicate evolutionary forces.
Allele
An alternative form of a gene at the same chromosomal locus; diploid organisms have two alleles per locus (may be homozygous or heterozygous); dominant allele masks recessive in heterozygotes.

Frequently Asked Questions

Law of Segregation (First Law): the two alleles of each gene separate during meiosis so each gamete receives only one allele per gene. Law of Independent Assortment (Second Law): alleles for different gene pairs assort independently into gametes — holds when genes are on different chromosomes (not linked). These laws predict: monohybrid cross (Aa × Aa) → 3:1 phenotype ratio; dihybrid cross (AaBb × AaBb) → 9:3:3:1. Modern exceptions: incomplete dominance, codominance, epistasis, linkage, pleiotropy, and polygenic inheritance all modify simple Mendelian ratios.

Genotype: the specific alleles an organism carries (e.g., Bb = heterozygous for brown eye gene). Phenotype: the observable trait expressed (e.g., brown eyes). Same genotype can give different phenotypes depending on environmental conditions (phenotypic plasticity). Same phenotype can arise from different genotypes (genetic heterogeneity). Penetrance: the fraction of individuals with a specific genotype who express the expected phenotype (complete penetrance = 100%; incomplete penetrance means some carriers don't show the trait). Expressivity: the degree of trait expression — variable expressivity means different carriers show different severity.

Hardy-Weinberg equilibrium predicts genotype frequencies in a population with no evolutionary change: p² (homozygous dominant AA) + 2pq (heterozygous Aa) + q² (homozygous recessive aa) = 1, where p = frequency of allele A and q = frequency of allele a (p+q = 1). Conditions: large population; random mating; no selection; no mutation; no gene flow. Real populations deviate from HWE due to these evolutionary forces. Deviation from HWE is detectable by chi-square test. Used to: estimate carrier frequency (2pq) from disease frequency (q²); detect selection or non-random mating; analyze population structure in forensics.

Point mutations (single base changes): synonymous (silent) — codon changes but same amino acid; missense — different amino acid; nonsense — premature stop codon → truncated protein. Frameshift mutations: insertions or deletions not in multiples of 3; shift reading frame → abnormal protein sequence from mutation point onward. Splice-site mutations: disrupt intron/exon boundary → abnormal mRNA splicing. Copy number variants (CNVs): duplications or deletions of larger segments. Chromosomal rearrangements: translocations, inversions, amplifications. Effects range from silent to lethal depending on location and nature. Mutations in tumor suppressor genes (TP53, RB1) or oncogenes (RAS, EGFR) drive cancer.