Heredity
Formulas & Genetic Ratios
Study of inheritance of a single pair of contrasting characters (e.g., Tall vs Short plants).
↔ Swipe to view ratiosPhenotypic Ratio: $$3 : 1$$
(3 Tall : 1 Short)
Genotypic Ratio: $$1 : 2 : 1$$
(1 Pure Tall (TT) : 2 Hybrid Tall (Tt) : 1 Pure Short (tt))
Inheritance of two independent traits simultaneously (e.g., Round-Green vs Wrinkled-Yellow seeds).
Phenotypic Ratio: $$9 : 3 : 3 : 1$$
• 9 Round-Yellow (Both Dominant)
• 3 Round-Green (One Dominant, One Recessive)
• 3 Wrinkled-Yellow (One Recessive, One Dominant)
• 1 Wrinkled-Green (Both Recessive)
The probability of offspring being male or female is always exactly 1:1 (50%).
Female Gamete (Ovum): Always carries **X**
Male Gamete (Sperm): Carries either **X** or **Y**
$$\text{X (Egg)} + \text{X (Sperm)} \rightarrow \text{XX (Female child)}$$ $$\text{X (Egg)} + \text{Y (Sperm)} \rightarrow \text{XY (Male child)}$$
Formulas for understanding trait expression.
Genotype: The genetic makeup (e.g., Tt, tt)
Phenotype: The physical appearance (e.g., Tall, Short)
Alleles: Alternative forms of a gene (T or t)
Zygosity: Homozygous (TT/tt) or Heterozygous (Tt)