Summary
Monohybrid inheritance involves the inheritance of a single trait controlled by different alleles of a gene. It is used to predict the outcome of genetic crosses.
- Allele — different form of a gene. Example: Blue colour allele and brown colour allele for eye colour.
- Dominant allele — allele that is always expressed when present. Example: Denoted by an uppercase letter (B, G, T).
- Recessive allele — allele that is only expressed when a dominant allele is not present. Example: Denoted by a lowercase letter (b, g, t).
- Homozygous — when a gene has two identical alleles. Example: (BB) or (bb).
- Heterozygous — when a gene has two different alleles. Example: (Bb).
- Genotype — the genetic makeup of an organism in terms of alleles. Example: Homozygous or heterozygous.
- Phenotype — the physical characteristic of an organism due to its genotype and environment. Example: Blue eyes from a homozygous dominant genotype (BB).
Exam Tips
Key Definitions to Remember
- Allele
- Dominant allele
- Recessive allele
- Homozygous
- Heterozygous
- Genotype
- Phenotype
Common Confusions
- Mixing up dominant and recessive alleles
- Confusing genotype with phenotype
Typical Exam Questions
- What is a monohybrid cross? A genetic cross involving a single trait controlled by alleles.
- How do you determine the phenotype from a genotype? By identifying the dominant and recessive alleles present.
- What is the phenotype ratio for a monohybrid cross between two heterozygous parents? 3:1 (3 dominant phenotype: 1 recessive phenotype)
What Examiners Usually Test
- Ability to predict outcomes of monohybrid crosses
- Understanding of genotype and phenotype relationships
- Knowledge of dominant and recessive allele expression