When a particular mutagen identified by the Ames test is injected into mice, it causes the appearance of many tumors, showing that this substance is carcinogenic. When cells from these tumors are injected into other mice not exposed to the mutagen, almost all of the new mice develop tumors. However, when mice carrying mutagen-induced tumors are mated to unexposed mice, virtually all of the progeny are tumor free. Why can the tumor be transferred horizontally (by injecting cells) but not vertically (from one generation to the next)

because the mutagen induced tumor causing mutations in somatic cells, not in gamete producing cells in the germline.

Explanation:

The gene can be transferred either horizontally or by vertically.

The above scenario is related to horizontally transferred of mutagen by tumor cells to the non-exposed mutagen mice. By transfer of mutagen cells, tumor develop the mice. When mutagen-induced tumor mice are mated with unexposed mice, there will be no development of tumor into the progeny.

It clearly shows that mutation occurs in the somatic cells only due to mutagen and it does not affect the gamete producing cells in the germline.

fertilization, pictured in figure 24.23a is the process in which gametes (an egg and sperm) fuse to form a zygote. the egg and sperm each contain one set of chromosomes. to ensure that the offspring has only one complete diploid set of chromosomes, only one sperm must fuse with one egg. in mammals, the egg is protected by a layer of extracellular matrix consisting mainly of glycoproteins called the zona pellucida. when a sperm binds to the zona pellucida, a series of biochemical events, called the acrosomal reactions, take place. in placental mammals, the acrosome contains digestive enzymes that initiate the degradation of the glycoprotein matrix protecting the egg and allowing the sperm plasma membrane to fuse with the egg plasma membrane, as illustrated in figure 24.23b. the fusion of these two membranes creates an opening through which the sperm nucleus is transferred into the ovum. the nuclear membranes of the egg and sperm break down and the two haploid genomes condense to form a diploid genome.

explanation:

answer; ///(b) it is composed of four protein chains and four heme groups;