Amutation that disrupts the ability of an animal cell to add polysaccharide modifications to proteins would most likely cause defects in its

Golgi apparatus and extracellular matrix

Explanation:

The Golgi complex lies at the heart of the secretory pathway and is responsible for modifying proteins and lipids, as well as sorting newly synthesized molecules to their correct destination. As a consequence of these important roles, any changes in its proteome can negatively affect its function and in turn lead to disease.

Disruption of specific transport steps between the endoplasmic reticulum (ER), Golgi complex, endosomal-lysosomal system and the plasma membrane all can have dramatic consequences on the cell, and increasingly defects in the molecular machinery regulating membrane traffic are being linked to hereditary diseases.

Any changes to the proteome of the Golgi complex would affect its homeostasis and consequently the flux of proteins trafficking through it.

One possible consequence of mutations in Golgi complex proteins is that they cause gross changes in the morphology of the entire organelle and protein mislocalization, which together result in functional problems such as impairment of glycosylation.

Genetic studies of humans and mice continue to highlight the nonredundant mechanical role of components in complexes that anchor cells to extracellular matrices. At the same time, recent data provide exciting insights into, critical roles of transcription factors in regulating differentiation and function of matrix-producing cells.

multiple allele inheritance is traits controlled by more than 2 alleles (ex: pigeons having 3 alleles of one gene govern their feather color).   so the answer is a.