<prompt> Testis determining genesex determining region is located on:X chromosomeY chromosomeChromosome 21Chromosome 18  <response>: Ans: b Y chromosome Ref: Robbins, 7th ed,p. 181, Ganong, 22nd p. 411Y chromosome is necessary for the development of testes. The testes determining gene SRY - sex determining region on Y chromosome is located near the tip of the short arm of Y chromosome. This SRY is a DNA binding protein, it bends the DNA and initiates transcription of a cascade of genes necessary for testicular differentiation, including the gene for MIS During normal gametogenesis, as a consequence of meiosis each ovum contains one X chromosome, but half of the sperms contain an X chromosome and half contain a Y chromosome. When sperm withY chromosome fertilizes ovum, genetic male results. When sperm with X chromosome fertilizes ovum, genetic female results. 