All animals with eyes or eyespots that have been studied so far share a gene in common. When mutated, the gene Pax-6 causes lack of eyes in fruit flies, tiny eyes in mice, and missing irises (and other eye parts) in humans. The sequence of Pax-6 in humans and mice is identical. There are so few sequence differences with fruit fly Pax-6 that the human/mouse version can cause eye formation in eyeless fruit flies, even though vertebrates and invertebrates last shared a common ancestor more than 500 million years ago.

The appearance of Pax-6 in all animals with eyes can be explained in multiple ways. Based on the information above, which explanation is most likely?

#Question id: 5653

#Unit 5. Developmental Biology

Why is meiosis required for germ cell formation, yet is never used by somatic cells?

#Question id: 5654

#Unit 5. Developmental Biology

Two human disorders, Prader-Willi syndrome and Angelman syndrome, occur when a small deletion in a specific region of chromosome 15 is contributed by either the father or mother, respectively. Why does this small deletion not behave as a recessive allele for either syndrome, that is, why is its loss not made up for by the good copy of the region on chromosome 15 contributed by the other parent?

#Question id: 5655

#Unit 5. Developmental Biology

What is the "acrosomal reaction"?

#Question id: 5656

#Unit 5. Developmental Biology

What is the cortical reaction, and why is it important?

#Question id: 5657

#Unit 5. Developmental Biology

Following statements regarding to the molecular processes of capacitation.

A. The sperm cell membrane is altered by the removal of cholesterol by albumin proteins in the female reproductive tract.

B. Particular proteins or carbohydrates on the sperm surface are lost during capacitation.

C. The membrane potential of the sperm cell becomes more positive as potassium ions leave the sperm. This change in membrane potential may allow calcium channels to be opened and permit calcium to enter the sperm.

D. Calcium and bicarbonate ions are critical in activating cAMP production and in facilitating the membrane fusion events of the acrosome reaction.

E. As a result of cAMP formation, protein phosphorylation occurs. Once they are phosphorylated, some proteins migrate to the surface of the sperm head. One of these proteins is juno, which is critical in sperm-egg fusion.

which one of the following combinations is correct?

#Question id: 5658

#Unit 5. Developmental Biology

 Following events occur during fertilization in mammals.

A. sperm penetrates cumulus layer

B. sperm nucleus delivered into cytoplasm

C. sperm plasma membrane fuses with egg plasma membrane

D. calcium waves

E. enzymes released from acrosome on sperm head enable sperm to penetrate zona pellucida

F. transit through the cumulus or binding to zona pellucida elicits acrosomal reaction in sperm

G. egg completes meiosis and development is initiated

which of the following sequence is correct?