Page 146 - Canadian BC Science 9
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When a eukaryotic cell is ready to divide, each strand of chromatin coils up into a very compact, X-shaped structure called a chromosome. Figure 4.7 shows the relationship between DNA, chromatin, and chromosomes.
Figure 4.7 DNA, chromatin, and chromosome relationship
Every organism has a characteristic number of chromosomes
Chromosomes within the nucleus are found in pairs. Most human cells have 46 chromosomes arranged in 23 pairs, including one pair of chromosomes that help determine sex (Figure 4.8). In males, the 23rd pair of chromosomes is the XY pair. In females, it is the XX pair. Every living thing has a characteristic number of chromosomes, as shown in Table 4.1 on the next page.
Chromosomes of a human cell
123456 7 8 9 10 11 12
13 14 15 16 17 18
19 20 21 22 (XY)
Figure 4.8 The chromosomes of a human cell compared with the chromosomes of a fruit fly cell.
Chromosomes of a fruit fly cell
128
MHR • Unit 2 Reproduction
1 2 3 (XX)
