With the initial appearance of the feature we call “Now Solve This,” a short introduction is in order. The feature occurs several times in this and all ensuing chapters, each time providing a problem related to the discussion just presented. A “Hint” is then offered that may help you solve the problem. Here is the first problem:
- (a) If an organism has a diploid number of 16, how many chromatids are visible at the end of mitotic prophase?
- (b) How many chromosomes are moving to each pole during anaphase of mitosis?
(a)
To determine: The number of chromatids that are visible at the end of prophase stage of mitosis.
Introduction: Mitosis is a process of division in which two daughter cells produce, and each daughter cell has the same complement of chromosomes as the parent cell.
Explanation of Solution
Prophase is the first stage of mitosis. In this stage, chromatin fibers start to condense, and nuclear envelope disappears, and centrioles divide. As chromatin fibers condense, the thread-like structures, the chromosomes, become visible.
It becomes apparent near the end of prophase that each chromosome consists of two parts, which are called sister chromatids. For example, if an organism has diploid number of 16 chromosomes, 32 chromatids would be visible at the end of mitotic prophase.
(b)
To determine: The number of chromosomes that move towards the opposite poles during anaphase.
Introduction: Mitosis is divided into several stages: prophase, prometaphase, metaphase, anaphase, and telophase.
Explanation of Solution
In metaphase, the homologous chromosomes duplicate. Anaphase is the shortest stage of mitosis. The events critical to chromosome distribution occur during this stage. In this stage, sister chromatids of each chromosome disjoin from one other and are pulled towards opposite ends. This event is described as disjunction. If an organism has a diploid number of 16 chromosomes, 16 chromosomes will move towards the opposite poles during anaphase.
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