Embryology and Development Practice Questions

Q: Fertilization is complete when:

The second polar body is formed.. Fertilization is a complex sequence of events that begins with sperm-oocyte contact and ends with the intermingling of maternal and paternal chromosomes [2]. **Why Option B is correct:** At the time of ovulation, the secondary oocyte is arrested in **Metaphase of Meiosis II**. It remains in this state until a sperm penetrates the zona pellucida and the oocyte's plasma membrane [4]. This penetration triggers the "activation of the oocyte," which leads to the completion of Meiosis II. This division results in a mature ovum and the extrusion of the **second polar body** [2], [5]. Therefore, the formation of the second polar body is the definitive morphological sign that fertilization has been successfully initiated and the oocyte has completed its meiotic journey. **Why the other options are incorrect:** * **Option A:** The first polar body is formed at the end of Meiosis I, which occurs just before ovulation (triggered by the LH surge) [1]. * **Option C:** Primary oocytes are formed during fetal life and are arrested in Prophase I (Diplotene stage) until puberty [3]. * **Option D:** The secondary oocyte is the stage at which the egg is released during ovulation; it is the *target* of fertilization, not the completion of it. **High-Yield Facts for NEET-PG:** * **Site of Fertilization:** Usually the **Ampulla** of the fallopian tube [2]. * **Meiotic Arrests:** 1st arrest is at **Prophase I (Diplotene)** at birth; 2nd arrest is at **Metaphase II** at ovulation [3]. * **Cortical Reaction:** Triggered by sperm entry to prevent **polyspermy** (entry of more than one sperm). * **Zygote:** The unicellular organism formed after the fusion of male and female pronuclei [2].

Q: Cleft tongue and clefting of the mandibular alveolar process are seen in which of the following conditions?

Orofacial digital syndrome.. The correct answer is **Orofacial Digital Syndrome (OFDS)**, specifically Type I. This is an X-linked dominant condition characterized by malformations of the oral cavity, face, and digits. 1. **Why it is correct:** OFDS is defined by the triad of oral, facial, and digital anomalies. The hallmark oral features include a **lobulated or cleft tongue** (due to hamartomas), **clefting of the alveolar ridge** (specifically the mandibular process), and multiple thick frenula (hyperplastic frenula). These occur due to the failure of fusion of the lateral lingual swellings and the mandibular processes during embryogenesis. 2. **Analysis of Incorrect Options:** * **Median Cleft Face Syndrome:** Characterized by midline defects like hypertelorism, bifid nose, and cranium bifidum occultum, but typically does not involve the mandibular alveolar process or a cleft tongue. * **Van der Woude Syndrome:** The most common cause of syndromic orofacial clefts. It is characterized by **paramedian lip pits** on the lower lip associated with cleft lip and/or cleft palate, but not a cleft tongue. * **Ascher Syndrome:** A rare condition characterized by the triad of **double lip**, blepharochalasis (eyelid swelling), and non-toxic thyroid enlargement. **High-Yield Clinical Pearls for NEET-PG:** * **OFDS Type I** is lethal in males; it is seen almost exclusively in females. * **Key Oral Findings:** Lobulated tongue, accessory gingival frenula, and missing teeth (hypodontia). * **Digital Findings:** Syndactyly, brachydactyly, or clinodactyly. * **Systemic Association:** Polycystic kidney disease is a common late-stage complication in OFDS Type I.

Q: What is the persistent remnant of the axial artery of the upper limb?

Anterior interosseous artery. ### Explanation The development of the arterial system in the upper limb follows a specific embryological sequence. The **axial artery** is the primary primitive vessel that arises from the seventh cervical intersegmental artery and runs down the center of the developing limb bud. **Why the Anterior Interosseous Artery is Correct:** As the limb develops, the original axial artery undergoes significant remodeling. In the forearm, the axial artery persists as the **anterior interosseous artery** and the **median artery** (though the latter usually regresses). Therefore, the anterior interosseous artery is considered the direct continuation and persistent remnant of the primitive axial trunk in the distal forearm. **Analysis of Incorrect Options:** * **Radial and Ulnar Arteries (A & B):** These are not remnants of the axial artery. They appear later in development as new sprouts from the brachial artery (radial) and the axial trunk (ulnar) that eventually surpass the original axial vessel in size and functional importance. * **Posterior Interosseous Artery (D):** This vessel arises as a branch from the axial artery but is not considered its primary persistent remnant. **High-Yield NEET-PG Pearls:** * **Axial Artery Derivatives:** In the adult, the axial artery is represented by the **Axillary**, **Brachial**, **Anterior Interosseous**, and **Deep Palmar Arch**. * **The Median Artery:** Occasionally, the median artery (a branch of the axial artery) persists into adulthood, accompanying the median nerve. If it persists, it may contribute to the superficial palmar arch. * **Sequence of Development:** The axial artery appears first, followed by the ulnar artery, and finally the radial artery.

Q: When a horseshoe kidney develops, the ascent of the kidney is restricted by which structure?

Inferior mesenteric artery. ### Explanation **1. Why Inferior Mesenteric Artery (IMA) is Correct:** During normal embryological development, the kidneys originate in the pelvis and gradually ascend to their adult position in the upper abdomen (T12–L3). In the case of a **Horseshoe Kidney**, the lower poles of the two kidneys fuse across the midline, forming an "isthmus" of renal or fibrous tissue. As this fused U-shaped mass ascends from the pelvis, it encounters the **Inferior Mesenteric Artery (IMA)**, which arises from the abdominal aorta at the level of **L3**. The isthmus becomes trapped under the IMA, preventing further cranial migration. Consequently, a horseshoe kidney is always located lower in the abdomen than normal kidneys. **2. Why the Other Options are Incorrect:** * **A, B, & C (Iliac Arteries):** The internal, external, and common iliac arteries are located inferior to the final resting position of the kidneys. While the kidneys pass through the bifurcation of the common iliac arteries during early ascent, these vessels do not act as a permanent anatomical barrier to the fused isthmus in the same way the IMA does at the L3 level. **3. Clinical Pearls & High-Yield Facts for NEET-PG:** * **Most Common Site of Fusion:** Lower poles (90% of cases). * **Level of Isthmus:** Typically found at the level of L3–L5. * **Associated Risks:** Increased incidence of **nephrolithiasis** (stones) and **hydronephrosis** due to the high insertion of the ureter and impaired urinary drainage. * **Vascular Supply:** Often characterized by multiple accessory renal arteries arising directly from the aorta or iliac vessels. * **Turner Syndrome:** Horseshoe kidney is the most common renal anomaly associated with Turner Syndrome (45, XO).

Q: Which of the following is indicated by the pedigree given below?

Identical twins. ***Identical twins*** - **Monozygotic twins** are represented in pedigrees by two descent lines that converge to a **single point** before connecting to the parents. - This symbol indicates that the twins originated from **one fertilized egg** that split, making them genetically identical. *Adopted into family* - Represented by a **bracket pointing inward** toward the family line, indicating an individual brought into the family. - This symbol shows **non-biological** relationship with the family members. *Adopted out of family* - Shown by a **bracket pointing outward** away from the family line, indicating an individual given up for adoption. - This symbol represents someone who is **biologically related** but raised outside the family. *Nonidentical twins* - **Dizygotic twins** are depicted by a **horizontal bar** connecting two separate descent lines from the parents. - This symbol indicates twins from **two separate fertilized eggs**, making them genetically similar to regular siblings.

Q: Which of the following is NOT true regarding the development of the ovary?

Oocytes are mesodermal in origin. ### Explanation The development of the ovary is a complex embryological process involving three distinct sources: the coelomic epithelium, the underlying mesenchyme, and primordial germ cells. **Why Option C is the correct (false) statement:** Oocytes are **not** mesodermal in origin. They develop from **primordial germ cells (PGCs)**, which originate from the **epiblast** and later migrate from the wall of the **yolk sac** (near the allantois) along the dorsal mesentery of the hindgut to reach the genital ridges. They are considered **endodermal** in their site of origin during migration. **Analysis of other options:** * **Option A:** The ovary develops in the **genital (gonadal) ridge**, which is a thickening of the intermediate mesoderm on the posterior abdominal wall. * **Option B:** The **primary sex cords** (medullary cords) and **secondary sex cords** (cortical cords) are formed by the proliferation of the **coelomic epithelium**. In females, the cortical cords incorporate the germ cells to form primordial follicles. * **Option D:** At birth, the total number of primary oocytes is estimated to be approximately **2 million** [1]. This number reduces to about 40,000 by puberty, with only ~400 being ovulated during a woman's reproductive life [1]. **High-Yield Clinical Pearls for NEET-PG:** * **Migration Failure:** If PGCs fail to reach the genital ridges, the gonads do not develop (gonadal dysgenesis). * **Ectopic Germ Cells:** If PGCs stray from their migratory path, they may survive in extragonadal sites and give rise to **teratomas** (commonly in the sacrococcygeal region) [2]. * **Meiotic Arrest:** Primary oocytes begin their first meiotic division before birth but remain arrested in the **prophase (diplotene stage)** until puberty due to Oocyte Maturation Inhibitor (OMI) [1].

Q: Which of the following brainstem nuclei is not derived from the alar plate?

Hypoglossal. The development of the brainstem is organized by the **sulcus limitans**, which divides the neural tube into a dorsal **alar plate** (sensory) and a ventral **basal plate** (motor). 1. **Why Hypoglossal is correct:** The **Hypoglossal nucleus (CN XII)** is a General Somatic Efferent (GSE) nucleus. All motor nuclei of the cranial nerves, including the hypoglossal, originate from the **basal plate** [1]. Since the question asks for the structure *not* derived from the alar plate, the hypoglossal nucleus is the correct answer. 2. **Why the other options are incorrect:** * **Inferior olivary nucleus:** Although it has a motor-coordination function, it is embryologically derived from the **alar plate**. Cells from the alar plate migrate ventrally to form this nucleus in the medulla. * **Substantia nigra:** Located in the midbrain, this structure is derived from the **alar plate** (specifically the marginal zone) [3] despite its functional association with the basal ganglia. * **Dentate nucleus:** As part of the cerebellum, it originates from the **rhombic lips**, which are specialized cranial extensions of the **alar plate** [2]. **High-Yield NEET-PG Pearls:** * **Basal Plate (Motor):** Gives rise to GSE (III, IV, VI, XII), SVE (V, VII, IX, X, XI), and GVE (Parasympathetic) columns. * **Alar Plate (Sensory):** Gives rise to sensory nuclei (GSA, SSA, GVA, SVA) and "migratory" nuclei like the **Pontine nuclei**, **Inferior olive**, and **Red nucleus**. * **Mnemonic:** **M-B / S-A** (Motor-Basal / Sensory-Alar). Remember that "migratory" relay nuclei are almost always Alar in origin.

Q: Posterior one-third of the tongue develops from which embryonic structure?

Hypobranchial eminence. **Explanation:** The development of the tongue is a high-yield topic involving the fusion of several swellings from the floor of the pharyngeal arches. **1. Why Hypobranchial Eminence is Correct:** The **posterior one-third (pharyngeal part)** of the tongue is derived from the **hypobranchial eminence** (also known as the copula of His). This structure is formed by the mesoderm of the **3rd and 4th pharyngeal arches**. Specifically, the 3rd arch mesoderm overgrows the 2nd arch, which explains why the sensory nerve supply to this region is the **Glossopharyngeal nerve (CN IX)**. **2. Analysis of Incorrect Options:** * **A & B (Lingual swellings and Tuberculum impar):** These structures arise from the **1st pharyngeal arch**. They fuse to form the **anterior two-thirds (oral part)** of the tongue. This is why the general sensation of the anterior tongue is carried by the Lingual nerve (branch of CN V3). * **D (Tongue bud):** This is a generic term and not a specific embryological structure used to define the posterior third's development. **3. NEET-PG Clinical Pearls & High-Yield Facts:** * **Muscles of the Tongue:** All muscles (except Palatoglossus) are derived from **occipital myotomes** and are supplied by the **Hypoglossal nerve (CN XII)**. * **Palatoglossus:** The only tongue muscle derived from the 4th arch (pharyngeal plexus/CN X). * **Foramen Caecum:** Represents the site of the original attachment of the thyroglossal duct; it marks the junction between the anterior 2/3 and posterior 1/3. * **Taste Sensation:** Anterior 2/3 is supplied by the **Chorda tympani (CN VII)**; Posterior 1/3 is supplied by the **Glossopharyngeal nerve (CN IX)** [1].

Q: The 4th aortic arch is responsible for the formation of which structure?

Arch of aorta. The aortic arches are a series of six pairs of mesenchymal vessels that arise from the aortic sac. Each arch has a specific fate in the development of the arterial system. [1] **Explanation of the Correct Answer:** The **4th aortic arch** develops differently on each side: * **Left side:** It forms part of the **arch of the aorta** (specifically the segment between the left common carotid and the left subclavian artery). [1] * **Right side:** It forms the proximal part of the **right subclavian artery**. Therefore, Option A is the correct derivative. **Why Other Options are Incorrect:** * **B. Pulmonary artery:** The proximal part of the **6th aortic arch** forms the pulmonary arteries (the left 6th arch also forms the Ductus Arteriosus). * **C. Pulmonary vein:** These develop from a sprout of the dorsal atrial wall, not from the aortic arch system. * **D. Subclavian vein:** Veins develop from the cardinal, vitelline, and umbilical venous systems, not the arterial aortic arches. **High-Yield NEET-PG Clinical Pearls:** * **1st Arch:** Maxillary artery (Mnemonic: **1**st is **M**axillary). * **2nd Arch:** Stapedial artery and Hyoid artery (Mnemonic: **S**econd is **S**tapedial). * **3rd Arch:** Common Carotid and proximal Internal Carotid arteries (Mnemonic: **C** is the **3**rd letter). * **5th Arch:** Rudimentary and disappears completely. * **Recurrent Laryngeal Nerve:** The relationship between the nerve and the arches explains why the left nerve loops under the Arch of Aorta (remnant of 4th/6th) [2] while the right nerve loops under the Right Subclavian (remnant of 4th). [2]

Q: Which is the earliest system to become functional in a fetus?

Circulatory System. The **Circulatory System** is the first organ system to become functional in the human embryo. This is a high-yield concept in embryology, as the rapidly growing embryo can no longer satisfy its nutritional and oxygen requirements by simple diffusion alone. ### Why the Circulatory System is Correct: * **Timeline:** Heart development begins in the 3rd week of gestation. The primitive heart tube begins to beat and circulate blood by the **end of the 3rd week (approximately day 21 or 22)**. * **Mechanism:** Angiogenesis and vasculogenesis occur in the extraembryonic mesoderm (yolk sac) and intraembryonic mesoderm to establish a functional circuit early to support rapid organogenesis [1]. ### Why Other Options are Incorrect: * **CNS (Option A):** While the neural plate forms in the 3rd week, the system does not become "functional" (in terms of complex reflex arcs or integrated activity) until much later in the first and second trimesters. * **GIT (Option B):** The primitive gut tube forms during the 4th week due to cephalocaudal and lateral folding, but functional maturation (peristalsis and enzyme production) occurs much later [1]. * **Genitourinary System (Option D):** The pronephros appears in the 4th week but is non-functional. The functional permanent kidneys (metanephros) only begin producing urine around the **10th–12th week**. ### NEET-PG High-Yield Pearls: * **First Sign of Life:** The heartbeat is the first sign of a functional system, detectable by Transvaginal Sonography (TVS) by the 5th–6th week of gestation. * **Progenitor:** The heart develops from the **splanchnic mesoderm** (cardiogenic area). * **Hematopoiesis:** The first site of blood formation is the **yolk sac** (3rd week), followed by the Liver (6th week), Spleen (12th week), and Bone Marrow (28th week) [1]. Remember the mnemonic: **"Young Liver Synthesizes Blood"** (Yolk sac → Liver → Spleen → Bone marrow).

Question 1

Fertilization is complete when:

Accepted Answer

The second polar body is formed.

Answer

The first polar body is formed.

Answer

The primary oocyte is formed.

Answer

The secondary oocyte is formed.

Question 2

Cleft tongue and clefting of the mandibular alveolar process are seen in which of the following conditions?

Accepted Answer

Orofacial digital syndrome.

Answer

Median cleft face syndrome.

Answer

Vander Woude syndrome.

Answer

Ascher syndrome.

Question 3

What is the persistent remnant of the axial artery of the upper limb?

Accepted Answer

Anterior interosseous artery

Answer

Radial artery

Answer

Ulnar artery

Answer

Posterior interosseous artery

Question 4

When a horseshoe kidney develops, the ascent of the kidney is restricted by which structure?

Accepted Answer

Inferior mesenteric artery

Answer

Internal iliac artery

Answer

External iliac artery

Answer

Common iliac artery

Question 5

Which of the following is indicated by the pedigree given below?

Accepted Answer

Identical twins

Answer

Adopted into family

Answer

Adopted out of family

Answer

Nonidentical twins

Question 6

Which of the following is NOT true regarding the development of the ovary?

Accepted Answer

Oocytes are mesodermal in origin

Answer

Develops in the genital ridge

Answer

Sex cords are derived from the coelomic epithelium

Answer

At birth, the ovary contains 2 million follicles

Question 7

Which of the following brainstem nuclei is not derived from the alar plate?

Accepted Answer

Hypoglossal

Answer

Inferior olivary

Answer

Substantia nigra

Answer

Dentate

Question 8

Posterior one-third of the tongue develops from which embryonic structure?

Accepted Answer

Hypobranchial eminence

Answer

Lingual swellings

Answer

Tuberculum impar

Answer

Tongue bud

Question 9

The 4th aortic arch is responsible for the formation of which structure?

Accepted Answer

Arch of aorta

Answer

Pulmonary artery

Answer

Pulmonary vein

Answer

Subclavian vein

Question 10

Which is the earliest system to become functional in a fetus?

Accepted Answer

Circulatory System

Answer

Central Nervous System (CNS)

Answer

Gastrointestinal Tract (GIT)

Answer

Genitourinary System

Embryology and Development — MCQs

Embryology and Development — MCQs

On this page

Practice by Chapter

Want unlimited practice?