The scientist who first observed and described living microorganisms (animalcules) using a single-lens microscope was: MCQ with Answer and Explanation

Explanation:
In the XX-XY system of sex determination, found in humans and most mammals, females have two identical sex chromosomes (XX) and are homogametic, producing only X-bearing eggs. Males have two different sex chromosomes (XY) and are heterogametic, producing two types of sperm: 50% with X and 50% with Y. The sperm determines the sex of the offspring.

Explanation:
Klinefelter syndrome is a sex chromosomal aneuploidy in males characterized by the karyotype 47, XXY. Individuals are phenotypically male but often exhibit feminine characteristics such as gynecomastia (development of breasts), sparse body hair, and are typically sterile due to underdeveloped testes. Down syndrome is trisomy 21 (47, +21), Turner syndrome is 45, X0, and Patau syndrome is trisomy 13.

Explanation:
Thyroid-stimulating hormone (TSH) from the anterior pituitary binds to thyroid follicular cells, stimulating the release of T₃ and T₄.