Question 1

Which of the following statements best explains why mitochondrial DNA (mtDNA) is almost entirely maternally inherited in most animals?

Accepted Answer

Sperm mitochondria degenerate after fertilization, so all mitochondria in the zygote come from the egg.

Question 2

In frog development, what is the significance of the 'gray crescent' formed after fertilization?

Accepted Answer

It marks the future site of the blastopore and is essential for normal embryonic development.

Question 3

Which experimental result led Hans Spemann to conclude that cytoplasmic determinants in the gray crescent are necessary for gastrulation?

Accepted Answer

Bisecting a salamander embryo so that only one half received the gray crescent resulted in only that half developing normally.

Question 4

During cleavage in animal development, what is the primary function of compaction in mammalian embryos?

Accepted Answer

It separates the inner cell mass from the trophoblast, establishing the origin of embryonic stem cells.

Question 5

Which of the following best describes the process of gastrulation?

Accepted Answer

Transformation of a blastula into an embryo with three tissue layers: ectoderm, mesoderm, and endoderm.

Question 6

In vertebrate development, what is the role of induction in the formation of the eye?

Accepted Answer

Signals from the optic vesicle induce surface tissue to form the lens and cornea.

Question 7

Which of the following statements about blastomeres and inner cell mass (ICM) cells is correct?

Accepted Answer

They are totipotent and can form an entire organism if separated.

Question 8

What is the main difference between holoblastic and meroblastic cleavage?

Accepted Answer

Holoblastic cleavage divides the entire egg, while meroblastic cleavage divides only part of the egg due to the presence of a large yolk.

Question 9

Which equation best represents the relationship between the number of somites ($$n) $$and the number of vertebrae ($$v) in a $$segmented animal, assuming each somite forms one vertebra?

Accepted Answer

$$v = n$$

Question 10

In nematode development, what is the function of the anchor cell and the LIN-3 factor?

Accepted Answer

The anchor cell secretes LIN-3, which induces nearby epidermal cells to differentiate into vulva cells via a Ras/MAPK pathway.

Question 11

Which of the following is a direct consequence of the formation of the primitive streak in bird and reptile embryos?

Accepted Answer

Cells migrate through the streak and become endoderm and mesoderm.

Question 12

What is the primary embryonic organizer in amphibian development, and what is its function?

Accepted Answer

The dorsal lip of the blastopore; it can induce other cells to participate in embryogenesis.

Question 13

Which of the following best describes the fate map of a frog embryo?

Accepted Answer

It shows the regions of the blastula that will give rise to specific tissues such as ectoderm, mesoderm, and endoderm.

Question 14

Which process is responsible for transforming the neural plate into the neural tube during neurulation?

Accepted Answer

The edges of the neural plate thicken, form ridges, and fuse to create a cylinder.

Question 15

Which extraembryonic membrane in chickens is responsible for gas exchange and waste removal?

Accepted Answer

The allantoic membrane

Question 16

In human development, which structure forms from the trophoblast and is essential for gas and nutrient exchange with the mother?

Accepted Answer

Placenta

Question 17

Which diagnostic technique allows for earlier detection of chromosomal and genetic defects in human embryos compared to amniocentesis?

Accepted Answer

Chorionic villus sampling (CVS)

Question 18

Which of the following is NOT a direct result of cell movements during gastrulation?

Accepted Answer

Formation of the neural tube

Question 19

Which formula best describes the relationship between the number of cells ($$N) $$after $$n$$ rounds of cleavage, starting from a single zygote?

Accepted Answer

$$N = 2^n$$

Developmental Biology: Stages and Mechanisms of Animal Development

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