Genotype
Genotype refers to the complete genetic constitution of an organism — specifically, the set of alleles present at a given locus or across all loci in the genome. Unlike phenotype (the observable characteristics), genotype is the underlying inherited sequence information that, in combination with environmental influences, determines the traits of an organism. Determining genotype is fundamental to genetic counselling, disease risk assessment, and molecular breeding programmes.
Genotype vs Phenotype for a Monohybrid Cross (Tt × Tt)
| Genotype | Allele Composition | Phenotype | Frequency in F2 |
|---|---|---|---|
| TT | Homozygous dominant | Tall plant | 25% (1/4) |
| Tt | Heterozygous | Tall plant (T dominant) | 50% (2/4) |
| tt | Homozygous recessive | Short plant | 25% (1/4) |
| Phenotypic ratio | — | Tall : Short = 3 : 1 | — |
| Genotypic ratio | — | TT : Tt : tt = 1 : 2 : 1 | — |
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Related Terms
Allele
An allele is one of two or more alternative forms of a gene that occupy the same locus (position) on homologous chromosomes. In diploid organisms, each individual carries two alleles for each gene — one inherited from each parent — and these alleles may be identical (homozygous) or different (heterozygous). The interaction between alleles (dominance, co-dominance, incomplete dominance) determines the phenotype expressed by an individual.
Gene
A gene is a specific sequence of DNA (or RNA in some viruses) that encodes the information required to produce a functional product, most commonly a protein or functional RNA molecule. Genes occupy defined loci on chromosomes and are the fundamental units of heredity, transmitted from parent to offspring. The modern molecular definition encompasses not only coding sequences (exons) but also regulatory elements such as promoters and enhancers that control when, where, and how much a gene is expressed.
Chromosome
A chromosome is a long, thread-like structure composed of DNA and associated histone proteins (chromatin) that carries genes in a linear sequence. In humans, the diploid somatic cells contain 46 chromosomes (23 pairs), with each chromosome harbouring thousands of genes. Chromosomes are visible under a light microscope during cell division and are essential for the accurate segregation of genetic material to daughter cells.
From Greek "genos" (birth, origin) + Greek "typos" (impression, type, pattern). The term was coined by Wilhelm Johannsen in 1909 simultaneously with "phenotype" and "gene" to distinguish the hereditary constitution from its outward expression.