In frogs, the gray crescent appears
a. after the egg matures.
b. after fertilization.
c. during blastula formation.
d. following gastrulation.
e. as a result of tissue specialization.
Answer: b
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A tracheid is:
A. a gametophyte cell B. a small branch of an insect trachea C. a seed-bearing stem D. a specialized vascular cell E. a reproductive chamber
Answer the following statements true (T) or false (F)
1. Two species of three-spined stickleback fish live in a single lake in British Columbia. They are closely related but occupy different niches. They exist nowhere else. These species most likely arose by sympatric speciation from a single species of three-spined stickleback. 2. The pace of evolution remains constant despite sudden environmental shifts such as climate change. 3. Although most genetic sequence information is obtained from living species, it is sometimes possible to obtain DNA from small tissue samples of extinct species for use in constructing phylogenetic trees. 4. Alan Cooper, Cécile Mourer Chauviré, Geoffrey Chambers, Arndt von Haeseler, Allan Wilson and Svante Pääbo investigated the evolutionary relationships among some extinct and living species of flightless birds using tissue samples from museums and from living birds. This is an example of discovery-based science.
After replication, in eukaryotic cells, both the original and its replicated copy chromosome are each called a
A. nucleosome. B. sister chromatid. C. centromere. D. chromatin. E. chromosome.
One hypothesis for why we age, or at least why our cells age, is that every time that mitosis occurs, ________ at the ends of chromosomes shorten, and eventually the cell runs out of these units at the ends of chromosomes
Fill in the blank(s) with correct word