Question 1

A woman ovulates two eggs that are fertilized by different sperm.The embryos implant and develop to full term.The two babies the woman gives birth to are

Accepted Answer

Non-identical twins, also known as fraternal twins, result from the fertilization of two separate eggs by two separate sperm. They share about 50% of their genes, similar to any other siblings, but are not genetically identical. They can be of the same or different sexes.

Question 2

A researcher exposes a sea urchin blastula to a protein that inhibits filopodia formation.Which event will most immediately be compromised in the manipulated blastula?

Accepted Answer

The answer of A researcher exposes a sea urchin blastula...

Question 3

Parthenogenesis is the development of unfertilized eggs.Which is the most reasonable assumption about a parthenogenetic species?

Accepted Answer

Centrosomes are responsible for organizing the microtubule cytoskeleton during many aspects of the cell cycle, including mitosis. In a parthenogenetic species, since there is no sperm contribution, the first centrosome must arise from maternal sources alone. This suggests that the egg can assemble the first centrosome without a sperm contribution.

Answer: D
 Centrosomes are important for mitotic spindle assembly and chromosome segregation during cell division. If a species undergoes parthenogenesis, it suggests that the eggs can undergo cell division without the need for a sperm contribution, indicating that the eggs can also undergo cell division without a centrosome.

Question 4

Refer to the figure showing the expression of the Hoxb gene cluster in a mouse.   Based on the figure, you can conclude that

Accepted Answer

The answer of Refer to the figure showing the expression...

Question 5

The urinary waste of birds is primarily uric acid, which looks like a white paste when released from the bird.When a chick hatches from its shell, you can see this white paste, which had been deposited in the _______, where it was being stored during incubation.

Accepted Answer

The answer of The urinary waste of birds is primarily...

Question 6

An X ray shows that a patient has a region in her upper spine where several vertebrae are fused on one side, causing curvature of the spine.The doctor tells her that the defect occurred during embryogenesis when

Accepted Answer

The curvature of the spine due to several vertebrae being fused on one side is most accurately explained by a defect in the somites during embryogenesis. Somites are blocks of mesoderm that segment along the embryo's axis and give rise to the vertebrae, among other structures. If a portion of several somites on one side fused abnormally, it could lead to the described spinal curvature.

Question 7

You find some marine eggs that were recently laid.The eggs are small with clear cytoplasm.You stain one egg for yolk and find faint staining relatively evenly distributed throughout the cytoplasm.When cleavage begins in the unstained eggs, you are not surprised to see that the pattern of cleavage is

Accepted Answer

The description of the eggs as small with clear cytoplasm and faint, evenly distributed yolk staining suggests that they are likely from an organism that undergoes spiral cleavage, a pattern characteristic of many marine invertebrates, particularly those within the group Lophotrochozoa, such as mollusks and annelids. Spiral cleavage is marked by cells dividing at oblique angles to one another.

Question 8

A researcher studying the development of the eye in Xenopus (the clawed frog) is testing her hypothesis that the optic vesicle induces head ectoderm to form the lens of the eye.When she removes the optic vesicle on one side of the embryo, no lens forms on that side, indicating the optic vesicle is necessary for lens formation.What additional experimental result must she obtain to show that the optic vesicle is also sufficient for inducing lens formation?

Accepted Answer

To demonstrate that the optic vesicle is sufficient for lens formation, the researcher needs to show that its presence alone (without other specific conditions or tissues that normally induce lens formation) can induce lens formation in tissues that do not normally develop into a lens. Option C, where a lens forms when the optic vesicle is placed next to tissue that does not normally form a lens, directly tests and supports the sufficiency of the optic vesicle for lens induction.

Question 9

A researcher experimenting with amphibian embryos is able to prevent the expression of the transcription factor Goosecoid in early organizer cells.The most likely result of this intervention is that

Accepted Answer

Goosecoid is a transcription factor critical for head formation in early development. By preventing its expression, the factors that inhibit head formation are not suppressed, leading to a scenario where head formation is likely inhibited, aligning with option E.

Question 10

A researcher working with fruit fly embryos removes the cells containing the pole plasm at the posterior end of an embryo.In a second embryo, the researcher removes several cells just lateral to the ones containing pole plasm.If both embryos develop into larvae, it is most likely that

Accepted Answer

The removal of cells containing pole plasm at the posterior end of an embryo will result in a lack of germ cells in the gonads of the first larva. The pole plasm is necessary for germ cell formation. In the second embryo, the removal of cells just lateral to the ones containing pole plasm will not affect the formation of germ cells, so the second larva will have gonads that contain germ cells.

Question 11

Which statement about frog eggs and early development is true?

Accepted Answer

The answer of Which statement about frog eggs and early...

Question 12

You are conducting an experiment that requires you to start a treatment on amphibian embryos when the nervous system starts developing.At which stage will you start the treatment?

Accepted Answer

The stage when the ectoderm overlying the notochord flattens into a platelike structure and thickens marks the beginning of neural plate formation and the onset of neurulation, during which the neural tissue will eventually form into the brain and spinal cord. Therefore, this is the stage most appropriate for starting a treatment targeting the developing nervous system.

Question 13

If a chick embryo has a defect that prevents blood vessels from forming in its extraembryonic mesoderm, which extraembryonic membrane(s) will be affected?

Accepted Answer

The allantois and yolk sac are both involved in the formation of blood vessels in the extraembryonic mesoderm, so a defect in blood vessel formation would affect both these membranes.

Question 14

You find a microscope slide labeled "Whole mount of early cleavage stage embryo," but the part of the label identifying the organism is missing.Upon observing the embryo under the microscope, you see that the embryo was mounted when it was undergoing its second cleavage and that the two cleavage planes are at a right angle.From this, you are able to conclude that the embryo is from a(n)

Accepted Answer

The description of the cleavage planes being at right angles is characteristic of the rotational cleavage pattern seen in placental mammals.

Question 15

A woman in her second month of pregnancy has a miscarriage and is told that her developing embryo had implanted successfully but had poorly developed umbilical blood vessels.Which is the most likely cause of this malformation?

Accepted Answer

The extraembryonic membranes, such as the chorion and allantois, are responsible for the formation of blood vessels that carry nutrients and oxygen to the developing embryo. If these membranes are defective, it can lead to poorly developed umbilical blood vessels and ultimately result in a miscarriage.

Question 16

A man and a woman who are both carriers for cystic fibrosis are using in vitro fertilization and preimplantation genetic diagnosis to ensure their offspring will not be afflicted by cystic fibrosis.In the procedure, a cell is removed from the embryo at the eight-cell stage and analyzed for the mutant genes.An embryo that is not homozygous for the mutation is implanted in the woman and develops normally.Because development is normal in the embryo after a cell has been removed, you can conclude that human development

Accepted Answer

The fact that an embryo develops normally even after the removal of one cell at the eight-cell stage suggests that human development is regulative during early cleavage stages. This means that each cell is not irreversibly determined to a specific fate at an early stage, but can adjust its fate according to various signals from its surroundings.

Question 17

If you experimentally removed the GSK-inhibiting protein from a fertilized amphibian egg, a likely result would be

Accepted Answer

Glycogen synthase kinase-3 (GSK-3) inhibition is crucial for the stabilization and accumulation of β-catenin on the dorsal side of the embryo, which is essential for the proper establishment of the dorsal-ventral axis in amphibian embryos. Removing the GSK-inhibiting protein would lead to excessive GSK-3 activity, preventing the accumulation of β-catenin on the dorsal side, thereby disrupting the dorsal-ventral axis formation.

Question 18

Which result did Hans Spemann and Hilde Mangold, working with amphibian embryos, obtain?

Accepted Answer

The answer of Which result did Hans Spemann and Hilde...

Question 19

You pull an unlabeled video out of a box labeled "Amphibian and sea urchin gastrulation." While watching the video, you decide it must be a video of a sea urchin embryo and not an amphibian embryo because you see that

Accepted Answer

Sea urchin gastrulation is characterized by the invagination of cells at the vegetal pole of the embryo, a process not observed in amphibian gastrulation.

Question 20

You find a clay model of an embryo undergoing gastrulation and realize it must represent a reptile or bird and not an amphibian because

Accepted Answer

The presence of Hensen's node and the movement of cells labeled as notochordal mesoderm indicate that the embryo is undergoing neurulation, which is a characteristic of reptiles, birds, and mammals, but not amphibians. Amphibians undergo a simpler process called neuralation.

Quiz 43: Animal Development