Table 321 Proposed Number of Hox Genes in Various Extant and and Extinct

question 34

Multiple Choice

Table 32.1. Proposed Number of Hox Genes in Various Extant and Extinct Animals

-Two competing hypotheses to account for the increase in the number of Hox genes from the last common ancestor all bilaterians to the last common ancestor of insects and vertebrates are: (1) a single duplication of the entire 4-gene cluster, followed by the loss of one gene, and (2) 3 independent duplications of individual Hox genes. To prefer the first hypothesis on the basis of parsimony requires the assumption that

• A)the duplication of a cluster of four Hox genes is equally likely as the duplication of a single Hox gene.
• B)there is an actual process by which individual genes can be duplicated.
• C)genes can exist is spatial groupings called "clusters."
• D)clusters of genes can undergo disruption, with individual genes moving to different chromosomes during evolution.

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Definitions:

Muscle

A tissue in the body composed of fibers capable of contracting to effect bodily movement.

Shortens

The process or action of making something shorter in length or duration.

Striated Muscle

Muscle tissue that is marked by transverse dark and light bands, found in the skeletal muscles and cardiac muscle, enabling voluntary movements.

Prone Position

A body posture where one lies flat with the chest down and the back up.