If the last pair reflects whether the organism is male or female, which would this organism be? Explain how you know.
The correct answer and explanation is:
The organism would be male or female depending on the sex chromosomes present in the last pair of chromosomes in the karyotype. Humans typically have 46 chromosomes in total, organized in 23 pairs. Of these, 22 pairs are autosomes, and the 23rd pair consists of sex chromosomes. The sex chromosomes determine the biological sex of the organism.
In males, the last pair consists of one X chromosome and one Y chromosome (XY). In females, the last pair consists of two X chromosomes (XX). These sex chromosomes are crucial for determining sexual development and reproduction.
The X and Y chromosomes carry different genes that influence the development of male or female physical characteristics. The Y chromosome carries the SRY gene (Sex-determining Region Y), which triggers the development of male characteristics. In the absence of the Y chromosome, or if it is defective, the organism develops female characteristics.
In terms of how the sex is determined, the presence of a Y chromosome (specifically the SRY gene) typically leads to the development of male characteristics, while the absence of the Y chromosome (and the presence of two X chromosomes) leads to the development of female characteristics. The process is governed by the inheritance of these chromosomes during fertilization.
Thus, if the organism has a Y chromosome in the last pair, it is male. If the organism has two X chromosomes in the last pair, it is female. The specific arrangement of these chromosomes in the karyotype provides a clear indication of the organism’s biological sex.