EVOLUTION CONNECTION Living members of a vertebrate lineage can be very different from early members of the lineage, and evolutionary reversals (character losses) are common. Give examples that illustrate these observations, and explain their evolutionary causes.

Two black female mice are crossed with a brown male. In several litters, female I produced 9 black offspring and 7 brown; female II produced 57 black offspring. What deductions can you make about the inheritance of black and brown coat color in mice? What are the genotypes of the parents?

Why were the Tiktaalik fossils an exciting discovery for scientists studying tetrapod evolution?a. They are the earliest frog-like animal discovered to date.b. They show that tetrapods successfully colonized land much earlier than previously thought.c. They have a roughly equal combination of fishlike and tetrapod-like characteristics.d. They demonstrate conclusively that limbs evolved as lobe-fins dragged themselves from pond to pond during droughts.

Which of the following could be considered the most recent common ancestor of living tetrapods?a. a sturdy-finned, shallow-water lobe-fin whose appendages had skeletal supports similar to those of terrestrial vertebratesb. an armored, jawed placoderm with two pairs of appendagesc. an early ray-finned fish that developed bony skeletal supports in its paired finsd. a salamander that had legs supported by a bony skeleton but moved with the side-to-side bending typical of fishes

To estimate the relative abundance of the major phyla, calculate how many named species of arthropods, mollusks, and nematode worms exist per named species of chordate (the phylum containing vertebrates, including humans; see Table 30.1). Do you think these calculations are likely to be underestimates or overestimates? Why?

There is some evidence that pharyngeal slits occur in certain species of echinoderms that appear early in the fossil record. If confirmed, what do these data suggest?a. Echinoderms are chordates.b. Pharyngeal slits were present in the earliest echinoderms and lost later.c. Some lineages of echinoderms are more closely related to chordates than others.d. Pharyngeal slits should not be used as a trait in phylogenetic analysis.

There is some evidence that pharyngeal slits occur in certain species of echinoderms that appear early in the fossil record. If confirmed, what do these data suggest?a. Echinoderms are chordates.b. Pharyngeal slits were present in the earliest echinoderms and lost later.c. Some lineages of echinoderms are more closely related to chordates than others.d. Pharyngeal slits should not be used as a trait in phylogenetic analysis.

In garden peas, yellow seeds (Y) are dominant to green seeds (y), and inflated pods (I) are dominant to constricted pods (i). Suppose you have crossed YYII parents with yyii parents. List the genotype(s) of gametes produced by F1 individuals.

Consider the evolution of protostomes and deuterostomes (this chapter): (1) Compare adaptations in protostomes and deuterostomes for living on land. (2) Recall that changes in the expression patterns of tool-kit genes in arthropods such as insects enabled a dramatic diversification of their segmented appendages and bodies. Design an experiment to test whether this concept applies to vertebrates.