The ability of a population of fibroblasts to migrate along the surface of a tissue culture dish depends on adhesion between the cell surface and the extracellular matrix molecules coating the dish. The dish is coated with laminin, and the only cell-surface protein capable of binding laminin is a cell-adhesion protein called an integrin. Integrins are integral plasma-membrane proteins that function as heterodimers. Under these conditions the rate at which a fibroblast can migrate along the laminin coated culture dish is proportional to the strength of adhesion between the cell and the laminin substrate. The table below lists the rate of cell migration observed for fibroblasts genetically engineered to generate the indicated phenotypes. Microinjection into the cytoplasm of a wild. type cell of a solution of a synthetic peptide possessing the same sequence as the integrin beta subunit cytoplasmic domain would be expected to yield an average fibroblast-cell migration rat

Fibroblast Phenotype	Level of Integrin Heterodimer at the Cell Surface (percent of wild type)	Rate of Cell Migration (pm/min)
1. Wild type	100	2
2. Overexpression of the wild-type integrin alpha subunit	104	2
3. Overexpression of an integrin beta subunit lacking the cytoplasmic domain	96	0.6
4. Overexpression of the soluble cytoplasmic domain of an integrin beta subunit	98	0.6
5. Absence of the integrin alpha subunit	Less than 1	0.05

#Question id: 11152

#Unit 9. Diversity of Life Forms

When sufficient heat is applied, double-stranded DNA denatures into two single-stranded molecules as the heat breaks all of the hydrogen bonds. In an experiment, molecules of single-stranded DNA from species X are separately hybridized with putatively homologous single-stranded DNA molecules from five species (A-E). The hybridized DNAs are then heated, and the temperature at which complete denaturation occurs is recorded. Based on the data below, which species is probably most closely related to species X?

#Question id: 11153

#Unit 9. Diversity of Life Forms

A researcher wants to determine the genetic relatedness of several breeds of dog (Canis familiaris). The researcher should compare homologous sequences of __________ that are known to be __________.

#Question id: 11154

#Unit 9. Diversity of Life Forms

Concerning growth in genome size over evolutionary time, which of these does not belong with the others?

#Question id: 11155

#Unit 9. Diversity of Life Forms

Nucleic acid sequences that undergo few changes over the course of evolutionary time are said to be conserved. Conserved sequences of nucleic acids

#Question id: 11156

#Unit 9. Diversity of Life Forms

Species that are not closely related and that do not share many anatomical similarities can still be placed together on the same phylogenetic tree by comparing their

#Question id: 11157

#Unit 9. Diversity of Life Forms

Typically, mutations that modify the active site of an enzyme are more likely to be harmful than mutations that affect other parts of the enzyme. A hypothetical enzyme consists of four domains (A—D), and the amino acid sequences of these four domains have been determined in five related species. Given the proportion of amino acid homologies among the five species at each of the four domains, which domain probably contains the active site?