Question

Evaluate whether the origin of cell-to-cell attachment proteins in animals illustrates descent with modification. (See Concept 22.2.)

Short answer

Decent with modification involves two aspects; sharing of some features from the ancestral organism and addition of some new features to modify the organism or structure.

The cadherin protein found in animals has some resemblance with the cell attachment protein present in an ancestral organism (choanoflagellate) and also has some new structures added to it during evolution.

Step-by-step solution

Animals

Animals are eukaryotic organisms characterized by multicellular body structures. The organization of the cells and their differentiation accounts for the variation in different animal groups. The extant animals are broadly grouped as vertebrates (vertebrae) and invertebrates (without vertebrae).

Protein for cellular adhesion

The multicellular body of animals or any other multicellular organism is stabilized by the attachment of different body cells among themselves. This attachment is aided by protein molecules, and in animals, cadherin is the group of proteins that adhere from one cell to another.

Decent with modification

In an evolutionary context, descent with modification can be explained as that modified feature that shares some aspects with the ancestral organism and has some additional aspects which were not found in the ancestral organism. The addition of a new feature diversifies the organism from the ancestral group.

Cadherin is the animal protein responsible for cell-to-cell attachment, and it accurately illustrates descent with modification. This protein has several domains similar to the domains found in their ancestor choanoflagellate’s cadherin-like protein,

It also contains some unique domains (Conserved Domain Database - CCD) absent in choanoflagellate’s protein.