AP BIOLOGY

Detailed explanation-1: -Because each chromosome was duplicated during the S phase that occurred just before prophase I, each now consists of two sister chromatids joined at the centromere. This arrangement means that each chromosome has the shape of an X.

Detailed explanation-2: -At the onset of mitosis, the nuclear envelope breaks down and chromatin is progressively converted into a discrete set of rod-shaped structures known as metaphase chromosomes (Fig.

Detailed explanation-3: -The X chromosome in humans spans more than 153 million base pairs (the building material of DNA). It represents about 800 protein-coding genes compared to the Y chromosome containing about 70 genes, out of 20, 000–25, 000 total genes in the human genome. Each person usually has one pair of sex chromosomes in each cell.

Detailed explanation-4: -’ Typically seen only as a diffuse mass when the cell is going about its day-to-day business, chromosomes become tightly packed into very distinctive X-shaped rods during cell division. This tight packaging helps ensure that each of the two cells post-division receives an identical copy of the genome.

Detailed explanation-5: -So, the correct answer is ‘Metacentric’.