give two examples of any organism that depict XX - XY type of sex determination
Answers
Explanation:
humans and many other animal species, sex is determined by specific chromosomes. How did researchers discover these so-called sex chromosomes? The path from the initial discovery of sex chromosomes in 1891 to an understanding of their true function was paved by the diligent efforts of multiple scientists over the course of many years. As often happens during a lengthy course of discovery, scientists observed and described sex chromosomes long before they knew their function.
An idea inspired by the "X element"
By the 1880s, scientists had established methods for staining chromosomes so that they could be easily visualized using a simple light microscope. With this staining method, scientists were able to observe cell division and to identify the steps that occurred during both mitosis and meiosis (Figure 1).
A photomicrograph of chromosomes in a dividing cell is shown beside a schematic illustration of a cell in anaphase. In the photomicrograph, chromosomes are being pulled apart toward the cell's opposite poles, leaving an empty space between the two sets of chromosomes. The chromosomes resemble worms. In the illustration, the two sister chromatids of each chromosome have become separated due to the action of the spindle fibers and are shown migrating to opposite poles of the cell. There are two sets of green chromatids and two sets of orange chromatids. The spindle fibers are white. Arrows at the top and bottom of each cell indicate the axis along which the cell divides.
Figure 1: Cell division observed through the microscope (left) is redrawn to show the action of chromosomes (right). Arrows indicate the axis along which the cell divides.