. Adventures with animals and plants. Biology. 458 Organisijis Are Products of Heredity mid Envhonvient unit ix. Fig. 406 Mitosis in aii animal cell. Note two centrosonies near the micleiis in (/). How many pairs of chroinosomes in {2)? What is happening to the chro77iosomes in {3)? In (4)? How many chromosomes in each of the cells about to form in {<))? chromosomes have split lengthwise there are twice as many chromosomes in the cell as there had been originally. Next the two halves of each chromosome move apart until they are at opposite ends of the cell. If you now counted the chromosome
. Adventures with animals and plants. Biology. 458 Organisijis Are Products of Heredity mid Envhonvient unit ix. Fig. 406 Mitosis in aii animal cell. Note two centrosonies near the micleiis in (/). How many pairs of chroinosomes in {2)? What is happening to the chro77iosomes in {3)? In (4)? How many chromosomes in each of the cells about to form in {<))? chromosomes have split lengthwise there are twice as many chromosomes in the cell as there had been originally. Next the two halves of each chromosome move apart until they are at opposite ends of the cell. If you now counted the chromosomes at each end of the cell, you would find the same number at the two ends; and if you had counted the original number in the cell, you would find as many chromosomes at each end now as there were in the cell before it began to divide. A delicate membrane then forms around each group of chromosomes. In the meantime, the chromosomes change back into a chromatin network. Thus two new nuclei are formed, each like the nucleus from which it came. Each is exactly like the nucleus from which it came because it contains a string of genes which came from the original genes. When, shortly after this, the cell body splits, cell division has been completed. Two daughter cells have taken the place of the fertilized tq^^ cell. And each has the same kinds of chromosomes and genes as the fertilized t^^. The whole process in some organisms takes no more than half an hour. This complicated di- vision of the nucleus, in which each daughter cell receives one half of each chromosome with a complete set of genes, is known as mitosis (mit-toe'sis). Now illustrate the mitotic changes in the nucleus bv doing Exercise 2. You have just read about mitosis in the division of the fertilized t^g cell. When each of these daughter cells di- vides later, and, in fact, in every cell di- vision thereafter, the nucleus divides by mitosis. There is only one normal excep- tion to this; you will read about it soon. Mi
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