A monohybrid cross shows a 3:1 ratio. Explain the reason.
A monohybrid cross shows a 3:1 ratio because of dominance and segregation of alleles during gamete formation.
Key Idea
| Term | Meaning |
|---|---|
| Monohybrid Cross | Cross involving one trait |
| Dominance | One allele masks the other |
| Segregation | Alleles separate during gamete formation |
Example Cross
| Parents | Genotype |
|---|---|
| Both | Tt × Tt |
Punnett Outcome
| Gametes | T | t |
|---|---|---|
| T | TT | Tt |
| t | Tt | tt |
Result
| Genotype | Ratio | Phenotype |
|---|---|---|
| TT | 1 | Tall |
| Tt | 2 | Tall |
| tt | 1 | Short |
Phenotypic Ratio
3 Tall : 1 Short
Stepwise Understanding
Each parent produces T and t gametes
Gametes combine randomly
Three combinations have dominant allele (TT, Tt, Tt)
One combination is recessive (tt)
Dominant trait appears in 3 out of 4 cases
Important Concept
Dominant allele expresses in both homozygous and heterozygous conditions.
Real Insight
This ratio is theoretical, in small number of offspring it may not look exact, which confuses many students at first.
So 3:1 ratio comes from dominance and random combination of segregated alleles.