If the last pair reflects whether the organism is a male or female, which would the organism be?
The correct answer and explanation is:
To determine the sex of an organism based on its last pair of chromosomes, it is important to understand the chromosomal system of sex determination. In most animals, including humans, this system relies on a pair of sex chromosomes, which are typically designated as X and Y.
In organisms with a XY system of sex determination, the presence of two X chromosomes (XX) typically results in a female, while the presence of one X and one Y chromosome (XY) typically results in a male. The key determinant is the Y chromosome, which carries a gene known as SRY (Sex-determining Region Y). This gene triggers the development of male characteristics, including the formation of male reproductive organs.
For example, in humans, the presence of XY chromosomes indicates a male. The Y chromosome carries genes that are responsible for initiating the production of male hormones (androgens), which in turn influence the development of male secondary sexual characteristics, such as a deeper voice, facial hair, and the ability to produce sperm.
In contrast, the XX chromosome pair would indicate a female organism. The lack of a Y chromosome means there is no SRY gene, so the default development is female. In the absence of male hormones, females develop female reproductive organs and secondary sexual characteristics, such as breasts and wider hips.
It is important to note that some species may have different systems for sex determination. For example, in some reptiles, the sex of the offspring can be determined by environmental factors like temperature, rather than by chromosomal sex determination. However, the XY system is the most common form in mammals and many other species.