Monohybrid Inheritance

Chapter 5: Monohybrid Inheritance

• Monohybrid inheritance refers to the inheritance of a single characteristic controlled by different alleles.
• An allele is an alternative form of a gene that is responsible for a particular trait.
• The alleles that make up an individual’s genotype can be either homozygous (identical alleles) or heterozygous (different alleles).
• If an individual is heterozygous for a trait, the allele that determines the characteristic is called dominant, while the other is called recessive.
• Recessive traits only appear when both alleles are recessive, otherwise the dominant trait will be expressed.

Chapter 6: Punnett Squares and Probability in Monohybrid Inheritance

• A Punnett square is a tool used to predict the outcome of monohybrid crosses.
• It helps visualise the combinations of parental alleles and the likelihood of the offspring displaying a particular trait.
• In monohybrid cross, the phenotypic ratio of the offspring often is 3:1 (3 showing the dominant trait, 1 showing the recessive trait).

Chapter 7: Genetic Notation in Monohybrid Inheritance

• Geneticists use letters to represent alleles in order to describe genotypes and phenotypes.
• For instance, a dominant allele might be represented by ‘A’ and the recessive allele by ‘a’.
• A homozygous dominant organism would have the genotype ‘AA’, a homozygous recessive would be ‘aa’, and a heterozygous would be ‘Aa’.

Chapter 8: Complete Dominance and Co-dominance in Monohybrid Inheritance

• In complete dominance, the dominant allele completely masks the effect of the recessive allele in the heterozygote.
• However, in co-dominance, both alleles for a gene are fully expressed, and neither allele is recessive.
• An example of co-dominance in humans is the ABO blood type system.