Non-Mendelian Genetics, Codominance, Incomplete Dominance, etc. - Jan. 21

Linkage in Genetics

Genetic Linkage

• Definition: Physical association of genes on the same chromosome.

• Linked genes transmitted together during gamete formation

• Independent assortment principles may be violated due to linkage.

Genetic Recombination

• Occurs during crossing over in meiosis; results in recombinant genotypes.

• Recombinants are less frequent compared to parental types.

• Mechanism of Recombination: Involves breaking and rejoining of DNA between non-sister chromatids.

Linkage Mapping

• Genes arranged in a linear array based on distance; greater distance increases crossing over likelihood.

• 50+ map units behave independently, reflecting Mendel’s pea plant traits.

Observations of Non-Mendelian Patterns

• Some traits/ratios deviate from Mendelian expectations due to genetic phenomena.

Analyses of Pea Traits

• Dominant and Recessive traits observed in second-generation ratios demonstrate variability (e.g., seed shape, color, flower color).

Gene Mapping Based on Frequency of Recombination

• Correlation between frequency of recombinant offspring and gene distance; e.g., 19.6% recombination equals 19.6 map units.

Dominance Relationships

• Vary among alleles due to interactions that are not necessarily linked to fitness.

Conclusions

• The concepts of linkage, genetic recombination, and dominance relationships are critical for understanding inheritance patterns beyond those predicted by Mendel's laws.