Question

1.)The gap gene Kr is:

a	Regulated by two, separate Hb-binding sites.

b	Would be expressed in the anterior half of the embryo if an Hb-binding site that overlaps with GTF-binding sites were eliminated.

c	Would be expressed in the anterior half of the embryo if an Hb-binding site that does not overlap with GTF-binding sites were eliminated.

d	Would be expressed in a stripe that would be shifted toward the posterior in an embryo whose mother had extra copies of the Bicoid gene.

e	Is responsible for the separation between the two stripes of Gt expression.

2.) In a multicellular embryo that is NOT syncytial:

a	After a cell's chromosomes are replicated, each of two nuclei get one copy of each chromosome.

b	After a cell's chromosomes are replicated and distributed into two nuclei, the cytoplasm is divided into two cells separated by outer membranes.

c	Proteins cannot form a gradient.

d	The strategy used in Drosophila to specify the A-P axis (creating a gradient of a transcriptional activator) would not work.

e	Part of the strategy used in Drosophila to specify the A-P axis (localizing mRNAs asymmetrically in the oocyte) would work.

3.) In a multicellular animal that is NOT syncytial, when cell A releases a diffusible signal:

a	Adjacent cells will receive it.

b	Adjacent cells will receive only if they express the corresponding receptor protein.

c	Distant cells will receive it only if they express the corresponding receptor protein and the levels of diffused signal are sufficiently high to bind to that receptor.

d	Cells that receive the signal may alter their transcription of one or more inducible genes.

e	Cells that receive the signal may alter the localization of one or more constitutively expressed gene products (mRNA or protein)

Answer 1

Ans 2) strategy used in drosophila to specify anterior- posterior axis would not work because syncytial means multinucleated mass of cytoplasm that is not separated into cells. This process is occur in syncytical cells which create gradient of transcription factor but in option d without syncytial this strategy wont work.

3) when cell A release a diffusable signal also called morphogen distant cells receive it only if they express corresponding receptor protein and level of diffusable signal sufficiently high to bind to that receptor.