Question

54.

1. In mammals, individuals with two X chromosomes are female, and individuals with an X and a Y chromosome are male. It had long been known that a gene located on the Y chromosome was sufficient to induce the gonads to form testes, which is the main male-determining factor in development, and researchers sought the product of this gene, the so-called testes-determining factor (TDF). For several years, the TDF was incorrectly thought to be a zinc finger protein encoded by a gene called BoY.

   Which of the following observations would most strongly suggest that BoY might not be the TDF?

   	A.	A few of the genes that are known to be expressed only in the testes have binding sites for the BoY protein in their upstream regulatory sequences, but most do not.
   	B.	Expression of BoY in adult females does not masculinize them.
   	C.	BoY is not expressed in the adult male testes.
   	D.	Some XY individuals that develop into females have mutations in a different gene, SRY, but are normal at BoY.

55.

1. For a certain plant cell, the concentration of sucrose is 10 mM on the inside of the cell and 0.5 mM on the outside, whereas [Na⁺] is 0.5 mM on the inside of the cell and 10 mM on the outside. The membrane potential (Vm or Ψm) is 150 mV, and the temperature is 25°C.
   You may need to use the conversions °K = 273 + °C, M = 10³ mM, V = 10³ mV, and kcal/mol = 10³ cal/mol. Recall: R = 1.987 cal/mol·°K, F = 23,062 cal/mol·V, z = ion charge.

   	A.	–1.774 kcal/mol; an exergonic reaction
   	B.	+1.774 kcal/mol; an exergonic reaction
   	C.	+1.774 kcal/mol; an endergonic reaction
   	D.	–1.774 kcal/mol; an endergonic reaction

Answer 1

55. Most likely answer is D. Some XY individuals that develop into females have mutations in a different gene, SRY, but are normal at BoY.

Description :

Why no A: Few genes have binding sites in the upstream region for BoY proteins which does not rule out that BOY can be TDF

Why not B: In females expression of BOY suppressor proteins may have been deactivated during the early development of gonands. In adult females the X chromosomal products may regulate the action of BOY proteins. Hence this option also does not rule out that BOY can be TDF.

Why not C: BOY is not expresses in adult male testis. It might be due to expression of BOY proteins during the sex determination at early development. Hence this option does not rule out the BOY to be TDF protein.