Non-Mendelian Genetics Summary

Non-Mendelian Genetics Summary

  • Definition: Genetic inheritance patterns that do not follow Mendel's laws.

  • Key Types:

    • Incomplete Dominance: Neither allele is completely dominant; phenotype is a blend.

    • Codominance: Both alleles express equally in phenotype.

    • Multiple Alleles: More than two alleles exist for a trait; example: ABO blood types.

    • Polygenic Inheritance: Trait controlled by multiple genes, causing a continuous range of phenotypes.

  • Sex-Linked Traits: Genes located on sex chromosomes; they often affect males differently than females.

  • Environmental Influence: Phenotype can be affected by environmental factors in addition to genetics.

  1. Multiple Alleles

    • One Gene: Only one specific gene locus is involved.

    • More than Two Allele Options: In the population, there are three or more possible alleles for that single gene, though an individual still only inherits two.

    • Discrete Categories: This usually results in distinct phenotypes (like Blood Types A, B, AB, or O).

    • Example: The ABO blood group system, which involves alleles IAIA, IBIB, and ii.

  2. Polygenic Inheritance

    • Multiple Genes: Two or more different genes (at different loci) contribute to a single characteristic.

    • Additive Effect: Each gene has a small, cumulative effect on the final trait.

    • Continuous Range: This results in a spectrum of phenotypes (a Bell Curve) rather than distinct groups.

    • Example: Human skin color, which is influenced by at least three genes (A,B,CA,B,C), or height, which is controlled by hundreds of different genes.

Summary: Multiple Alleles is about many versions of a single gene; Polygenic Inheritance is about the interaction of many different genes.