Overview
This module introduces non-Mendelian patterns of inheritance, explaining how certain traits do not follow the simple dominant-recessive rules discovered by Gregor Mendel.
Introduction to Heredity and Inheritance Patterns
- Heredity is the passing of traits from parents to offspring through genes.
- Mendelian inheritance involves dominant and recessive alleles controlling traits, following specific patterns.
- Not all traits follow Mendel’s laws; some display non-Mendelian inheritance.
Non-Mendelian Patterns of Inheritance
- Non-Mendelian inheritance includes patterns such as incomplete dominance, codominance, and multiple alleles.
- These patterns result in more complex trait expressions than simple dominant-recessive relationships.
Incomplete Dominance
- In incomplete dominance, the heterozygous phenotype is a blend of the two parental traits.
- Example: In snapdragons, crossing red and white flowers produces pink offspring.
Codominance
- In codominance, both alleles in a heterozygous individual are fully expressed.
- Example: In some cattle, red and white coat color genes produce offspring with both red and white patches.
Multiple Alleles
- Some genes have more than two possible alleles, called multiple alleles.
- Example: Human blood types (A, B, O) are controlled by three alleles (IA, IB, i).
Key Terms & Definitions
- Heredity — the passing of traits from parents to offspring.
- Non-Mendelian Inheritance — inheritance patterns that do not follow Mendel’s laws.
- Incomplete Dominance — neither allele is completely dominant, resulting in a blended phenotype.
- Codominance — both alleles are expressed equally in the phenotype.
- Multiple Alleles — more than two possible alleles exist for a gene in the population.
Action Items / Next Steps
- Review examples of incomplete dominance, codominance, and multiple alleles.
- Complete practice exercises comparing Mendelian and non-Mendelian inheritance.
- Read the next section on sex-linked traits.