D18 - Non-Mendelian Genetics Part 2

Introduction

• Continuation of Non-Mendelian Genetics concepts.
• Focus on variations and exceptions to Mendelian inheritance.

Key Non-Mendelian Concepts

Incomplete Dominance

• Definition: A situation in genetics where one allele does not completely dominate another allele, resulting in a new phenotype.
• Example: Crossing red and white flowers to produce pink flowers.

Codominance

• Definition: A situation where both alleles in a gene pair are fully expressed.
• Example: Blood type AB in humans where both A and B alleles are expressed.

Multiple Alleles

• Definition: More than two possible alleles exist in a population for a given gene.
• Example: Human blood types (A, B, O), where the gene for blood type has several alleles.

Polygenic Inheritance

• Definition: Multiple genes contribute to a single phenotypic trait.
• Example: Human skin color and height, which are controlled by multiple genes.

Pleiotropy

• Definition: A single gene influences multiple phenotypic traits.
• Example: Sickle-cell disease, where one gene causes multiple symptoms.

Epistasis

• Definition: Interaction between genes where one gene masks or interferes with the expression of another.
• Example: Coat color in mice, where one gene can suppress the expression of other fur color genes.

Gene Linkage

• Definition: Genes located close together on the same chromosome tend to be inherited together.
• Example: Linked genes do not assort independently during meiosis.

Genomic Imprinting

• Definition: Genes are expressed in a parent-of-origin-specific manner.
• Example: Certain genetic conditions only express when inherited from a specific parent.

Important Concepts

Environmental Impact on Gene Expression

• Definition: Environmental factors can influence how genes are expressed.
• Example: Temperature affecting coat color in Siamese cats.

Non-Mendelian Ratios in Genetic Crosses

• Non-Mendelian genetics often result in ratios different from Mendelian 3:1 or 9:3:3:1.

Conclusion

• Non-Mendelian Genetics introduces complexity beyond simple dominant-recessive relationships.
• Understanding these patterns is essential for studying genetic diversity and inheritance.

These notes summarize the main points from Part 2 of the Non-Mendelian Genetics lecture, focusing on various genetic inheritance patterns beyond Mendel's initial findings.