69 XYY occurs due to:
Rationale:
69 XYY occurs due to Dispermic.
Dispermy, the fertilization of a single ovum by two spermatozoa, is the primary cause of triploidy, specifically 69,XYY. This event results in an extra set of paternal chromosomes, leading to a total of 69 chromosomes and often a double Y chromosome contribution from the two sperm. This genomic imbalance frequently results in early embryonic lethality due to the severe chromosomal abnormality.
B: Endomitosis Endomitosis is chromosome replication without nuclear or cellular division, leading to polyploidy within a single cell, not typically to a 69,XYY triploid zygote from fertilization errors.
C: Tetraploidy Tetraploidy (4n) results in 92 chromosomes (e.g., 92,XXXX or 92,XXYY), involving four complete sets, rather than the three sets (69 chromosomes) characteristic of triploidy like 69,XYY.
D: Nondisjunction MI Nondisjunction in meiosis I typically leads to aneuploidy (e.g., trisomy 21, monosomy X), involving an abnormal number of individual chromosomes, not a complete extra set of haploid chromosomes as seen in triploidy.
One of the following is true about telomerase:
Rationale:
The whole telomere has the same sequence.
Telomeres consist of repetitive non-coding DNA sequences at chromosome ends, protecting genetic information during replication. Telomerase maintains these repetitive sequences, which are typically short, tandem repeats, ensuring the entire telomere, though elongated by the enzyme, is composed of the same characteristic nucleotide pattern. This consistent, redundant sequence prevents critical gene loss and preserves chromosomal integrity.
A: inactivation of telomerase contributes for the extended lifespan of cancer cells. Telomerase activation, not inactivation, is a hallmark of cancer cells, enabling their immortality by preventing telomere shortening and replicative senescence.
B: it uses DNA template. Telomerase is a ribonucleoprotein, containing an RNA template that it uses to synthesize new DNA repeats at the telomere ends, making it a reverse transcriptase.
C: it extends the daughter DNA strand to become longer than the parental DNA. Telomerase extends the parental DNA strand (the template strand for lagging strand synthesis) to ensure complete replication of the lagging strand, not making the daughter strand longer.
The most common ovarian neoplasm in adolescents is
Rationale:
The most common ovarian neoplasm in adolescents is teratoma.
Teratomas, specifically mature cystic teratomas (dermoid cysts), represent the vast majority of ovarian neoplasms found in adolescent patients. These germ cell tumors contain tissues from all three embryonic germ layers, such as hair, teeth, or sebaceous material. Their prevalence in this age group makes them the primary consideration for ovarian masses, typically benign and often asymptomatic until growth causes symptoms or torsion.
A: cancer Cancer, while a concern, is less frequent than benign teratomas in adolescent ovarian neoplasms. Most adolescent ovarian tumors are benign, with malignant forms constituting a smaller percentage.
C: adenoma Adenomas are epithelial tumors, which are more common in older women. While they can occur, their incidence in the adolescent population is significantly lower compared to germ cell tumors like teratomas.
D: sinus endodermal tumors Sinus endodermal tumors, also known as yolk sac tumors, are malignant germ cell tumors. Although they affect adolescents, they are rare and do not represent the most common type of ovarian neoplasm in this age group.
One of the following is an example of an x-linked recessive disorder
Rationale:
Adrenoleukodystrophy is an example of an x-linked recessive disorder.
Correct Option Explanation:
Adrenoleukodystrophy (ALD) is indeed an X-linked recessive disorder primarily affecting males. It involves mutations in the ABCD1 gene on the X chromosome, leading to impaired breakdown of very long-chain fatty acids. This accumulation causes progressive demyelination in the brain and adrenal insufficiency. Females are typically carriers but can exhibit milder symptoms due to X-inactivation, illustrating its X-linked inheritance pattern.
Incorrect Options Explanation:
A: cystic fibrosis (CF) Cystic fibrosis is an autosomal recessive disorder caused by mutations in the CFTR gene, not located on a sex chromosome, impacting chloride transport and mucus production.
B: congenital adrenal hyperplasia Congenital adrenal hyperplasia is typically an autosomal recessive condition, most often caused by a deficiency in the 21-hydroxylase enzyme, unrelated to X-chromosome inheritance.
C: Gaucher disease Gaucher disease is an autosomal recessive lysosomal storage disorder, resulting from a deficiency of the enzyme glucocerebrosidase, with no direct X-linked inheritance pattern.
The BRAC1 gene is involved in regulating:
Rationale:
The BRAC1 gene is involved in regulating DNA repair.
BRCA1 is a tumor suppressor gene crucial for maintaining genomic integrity. It plays a vital role in homologous recombination, a major pathway for repairing double-strand breaks in DNA. Its protein product interacts with other proteins to detect and mend damaged DNA, preventing mutations. Proper BRCA1 function is essential for accurate genetic information transfer and preventing uncontrolled cell proliferation.
A: Cell division While BRCA1 indirectly influences cell division by ensuring healthy DNA, its primary regulatory role is not in the mechanics of mitosis itself. Its impact is upstream, on genomic stability.
B: Cell death BRCA1 is not a direct regulator of apoptosis; its primary function is to prevent damage that might trigger cell death or malignant transformation. Its role is protective, not executionary.
D: DNA replication BRCA1 does not directly control the process of DNA synthesis or unwinding during replication; rather, it acts to fix errors or damage that may occur during or after replication.
Which P arm of the following chromosomes carries rDNA genes?
Rationale:
Chromosome 15 carries rDNA genes on its P arm.
Acrocentric chromosomes, specifically 13, 14, 15, 21, and 22, possess nucleolar organizing regions (NORs) on their short (p) arms. These NORs contain clusters of ribosomal DNA (rDNA) genes, which are crucial for synthesizing ribosomal RNA (rRNA). Chromosome 15 is one of these five human acrocentric chromosomes, making its p arm a known location for these essential genetic sequences involved in ribosome biogenesis.
A: 3: Chromosome 3 is a large metacentric chromosome, not typically associated with carrying rDNA genes on its p arm. Its primary function does not involve NORs.
C: 6: Chromosome 6 is a large submetacentric chromosome. It does not possess the specific acrocentric morphology or nucleolar organizing regions where rDNA gene clusters are located.
D: 12: Chromosome 12 is a medium-sized submetacentric chromosome. It lacks the characteristic satellite stalks on its p arm that define the ac
Tetraploidy results from:
Rationale:
Tetraploidy results from Endomitosis after fertilization.
Tetraploidy, characterized by four sets of chromosomes (4n), arises when a diploid cell undergoes endomitosis. This process involves chromosome replication and nuclear division without subsequent cytoplasmic division, effectively doubling the chromosome number within a single cell. If this event occurs in a normally fertilized 2n zygote or early embryo, it leads directly to a tetraploid state.
A: Haploid sperm and haploid egg This standard fertilization event combines two haploid gametes (n+n), forming a normal diploid (2n) zygote. It establishes the foundational diploid state, not a tetraploid one.
C: Diploid sperm and diploid egg Fusion of two diploid gametes (2n+2n) would indeed yield a tetraploid (4n) zygote. However, the production of diploid gametes is an unusual occurrence, making this a rarer mechanism for tetraploidy.
D: Dispermy Dispermy occurs
A mentally retarded 15-year-old boy is found to have macroorchidism and large, prominent ears. He most likely has
Rationale:
D: fragile X syndrome is the most likely diagnosis.
Fragile X syndrome is the most probable diagnosis given the constellation of intellectual disability in an adolescent boy, accompanied by distinct physical features. Macroorchidism, characterized by enlarged testes, is a hallmark sign in post-pubertal males. Additionally, prominent ears are a common dysmorphic feature associated with this X-linked genetic condition, making it the most fitting diagnosis for these combined clinical findings.
A: cerebral giantism This condition involves excessive growth during childhood and often macrocephaly. While intellectual disability can occur, macroorchidism and prominent ears are not characteristic defining features, making it an unlikely fit for this specific presentation.
B: acromegaly This disorder results from adult growth hormone excess, causing gradual enlargement of extremities and facial features. It primarily affects adults and does not typically present with the intellectual disability or macroorchidism seen in this adolescent patient.
C: hypothyroidism This condition involves insufficient thyroid hormone, leading to symptoms like fatigue and cognitive slowing. While intellectual impairment can manifest, particularly if congenital, it does not account for the distinct macroorchidism or prominent ear morphology described.
An affected mother with hypertrophic pyloric stenosis (HPS), became pregnant. She came to you to explain the possibility of future affection of her kids. Of the following, the MOST likely true explanation is
Rationale:
Maternal history increases risk: sons ~20%, daughters ~7%.
Maternal history of hypertrophic pyloric stenosis significantly elevates the risk for offspring compared to the general population. This multifactorial inheritance pattern demonstrates a sex-influenced predisposition, where sons of an affected mother have a substantially higher probability of developing the condition (around 20%) than daughters (approximately 7%), reflecting the observed sex ratio in HPS.
A: same like general population (5 times more possible in sons) Maternal HPS history markedly increases the recurrence risk, making general population rates irrelevant. The five-fold greater male incidence applies generally, but the absolute probabilities are much higher with an affected mother.
B: daughter is more likely to be affected with 7-10% possibility This statement is incorrect because sons are considerably more likely to be affected than daughters, even with maternal history. While 7-10% is within a daughter's risk range, it misrepresents the comparative likelihood between genders.
C: sons are likely to be affected with about 30% and daughter 1-2% These specific percentages are too high for sons and too low for daughters, respectively, when considering maternal HPS history. Established recurrence risks indicate sons face roughly 20% and daughters approximately 7% affection rates.
Homeobox gene mutations have been associated with all of the following EXCEPT
Rationale:
Homeobox gene mutations have not been associated with type 1 diabetes mellitus.
Type 1 diabetes mellitus is an autoimmune condition where the immune system attacks pancreatic beta cells, leading to insulin deficiency. This pathology primarily involves immune system dysregulation and pancreatic islet cell destruction, not developmental patterning defects typically associated with homeobox gene mutations. Homeobox genes regulate body plan development; their disruption doesn't cause autoimmune destruction of endocrine glands.
A: hand-foot-uterus syndrome This syndrome is caused by mutations in the HOXA13 homeobox gene, which directly impacts limb and reproductive tract development, aligning with homeobox gene functions.
B: hypodontia Hypodontia, characterized by congenitally missing teeth, is frequently linked to mutations in homeobox genes like MSX1 and PAX9, crucial for odontogenesis and craniofacial patterning.
C: Waardenburg syndrome Certain types of Waardenburg syndrome, particularly Type I and Type III, are associated with mutations in the PAX3 gene, a homeobox gene involved in neural crest cell development and pigmentation.
Genes that normally prevent cell division are:
Rationale:
Tumor suppressors are genes that normally prevent cell division.
Tumor suppressor genes regulate the cell cycle, initiate apoptosis, and repair DNA damage, thereby actively inhibiting uncontrolled cell proliferation. Their primary function involves ensuring genomic stability and preventing the formation of tumors by halting cell division when abnormalities arise. Loss of function in these crucial genes contributes directly to cancer development.
B: Transcription factors Transcription factors are proteins that bind to specific DNA sequences, regulating the rate of gene transcription. They modulate gene expression broadly, not specifically preventing cell division themselves.
C: Proto-oncogenes Proto-oncogenes are normal genes promoting cell growth and division. When mutated, they become oncogenes, actively driving uncontrolled cell proliferation, which is the opposite of preventing division.
D: Growth factors Growth factors are signaling molecules that stimulate cell growth, proliferation, and differentiation. They actively promote cell division rather than inhibiting it, often through receptor binding.
In the routinely performed karyotype (G-banding). Which of the following would you expect to have more clinical impact and lead to a disease?
Rationale:
A deletion of a region with a light band would you expect to have more clinical impact and lead to a disease.
Deletions remove vital genetic material, often resulting in haploinsufficiency where the remaining single gene copy is insufficient for normal function. G-banding identifies these missing segments, which, especially in gene-rich light bands, disrupt critical protein synthesis and regulatory pathways. This loss of essential genomic content typically leads to severe developmental abnormalities and manifest disease states, carrying significant clinical implications.
A: A duplication of a region with a light band Duplications involve extra genetic material, which, while potentially disruptive to gene dosage, generally results in less severe clinical outcomes compared to the complete absence of crucial genes.
B: A duplication of a region with a light band Chromosomal duplications represent an increase in gene copies; cells often tolerate this gain more effectively than the complete loss of a gene. Phenotypes stemming from duplications are frequently less severe.
Cancer cells are considered to be:
Rationale:
Cancer cells are considered to be All of these.
Cancer cells exhibit several defining characteristics. They are transplantable, meaning they can be moved to a new host and continue to grow, forming new tumors. Their abnormal traits are heritable, passed to daughter cells during division. Furthermore, they are dedifferentiated, losing specialized features and reverting to a more primitive state, contributing to uncontrolled proliferation and malignancy. These combined attributes define their pathological nature.
A: Transplantable Cancer cells are indeed transplantable, capable of establishing new growths in a recipient organism. However, this option alone does not encompass all the fundamental characteristics of malignancy, which include other crucial cellular alterations.
B: Heritable The abnormal characteristics of cancer cells are heritable, meaning they pass their pathological traits to subsequent cell generations. Yet, focusing solely on heritability overlooks other critical aspects of cancer cell biology, such as their morphological changes.
C: Dedifferentiated Cancer cells often become dedifferentiated, losing their specialized structures and functions, adopting a more generalized, immature phenotype. While a key feature, dedifferentiation alone fails to describe the comprehensive suite of traits defining cancerous cells' aggressive behavior.
The karyotype where euchromatic regions stain more darkly and the light regions are heretochromatin is:
Rationale:
R-banding is the karyotype where euchromatic regions stain more darkly and the light regions are heterochromatin.
R-banding, or Reverse banding, involves heat denaturation before Giemsa staining, producing a pattern inverse to G-banding. This technique specifically highlights gene-rich, GC-rich euchromatic regions, causing them to stain darkly. Conversely, AT-rich heterochromatic regions, often found near centromeres, appear lighter. This distinct staining pattern is crucial for identifying chromosomal aberrations, particularly in distal chromosome segments, offering complementary information to other banding methods.
A: Q-banding: Q-banding uses quinacrine mustard, yielding fluorescent bands under UV light where AT-rich heterochromatin appears bright and euchromatin is dimmer. This pattern contrasts with the described dark euchromatin.
B: C-banding: C-banding specifically stains constitutive heterochromatin, primarily at centromeres, appearing as dark blocks. It does not produce a pattern of generally dark euchromatin and light heterochromatin across the chromosome arms.
C: G-banding: G-banding involves trypsin treatment and Giemsa, resulting in dark bands on AT-rich heterochromatin and light bands on gene-rich euchromatin. This pattern is precisely the opposite of the described dark euchromatin.
A 2-year-old girl with history of delayed speech, lonely play, and special hand movement (hand washing posture), the parents are healthy relative couple. The genetic cause of this disorder is MOST likely due to
Rationale:
The genetic cause of this disorder is MOST likely due to new mutation.
The described symptoms, including delayed speech, lonely play, and hand stereotypies, are highly characteristic of Rett syndrome. This neuro
Which of the following is not a familial cancer syndrome?
Rationale:
Waardenburg syndrome is not a familial cancer syndrome.
Waardenburg syndrome is a genetic disorder primarily characterized by hearing loss and changes in pigmentation of the hair, skin, and eyes. It
The most commonly used stain for metaphase chromosomes is?
Rationale:
The most commonly used stain for metaphase chromosomes is Giemsa stain.
Giemsa stain is universally preferred for visualizing metaphase chromosomes due to its ability to produce distinct banding patterns (G-bands) essential for karyotyping and identifying chromosomal abnormalities. This differential staining, requiring prior trypsin treatment, allows precise identification of each chromosome pair and structural rearrangements, making it indispensable in cytogenetics laboratories worldwide.
A: Quinacrine stain Quinacrine stain produces Q-bands through fluorescence microscopy, offering an alternative banding technique. However, it is less frequently employed than Giemsa staining for routine cytogenetic analysis due to its specialized equipment requirements.
C: Trypsin Trypsin is an enzyme used before Giemsa staining to partially digest chromosomal proteins, facilitating the differential banding patterns. It is a preparatory agent, not the primary stain itself for visualizing metaphase chromosomes.
D: Anticipation Anticipation is a concept referring to genetic disorders showing earlier onset or increased severity in successive generations. It has no relevance whatsoever to the biochemical process of staining metaphase chromosomes for microscopic examination.
Wilms' tumor (nephroblastoma), an embryonal malignancy of the kidney, is the most common renal tumor of childhood. The tumor suppressor WTI is associated with familial Wilms Tumor and its locus is IlpDNA was extracted from the normal tissue and tumor of a patient with Wilms' tumor, and from the blood of the patient's father and mother. Electrophoresis (southern blot) was performed for a polymorphic marker (A) which is close to WTI. Based on the figure, which of the following is the most likely to explain the mutation in this patient's cancer?
Rationale:
Loss of the normal chromosome 11 is the most likely explanation for the mutation in this patient's cancer.
In familial Wilms' tumor, the patient inherits one germline mutated
With a germ-line mutation:
Rationale:
With a germ-line mutation, all cells are affected.
A germ-line mutation originates in the reproductive cells (sperm or egg) and is therefore present in the zygote. Since the zygote is the single cell from which an entire organism develops through cell division and differentiation, every cell in the resulting individual will carry this specific mutation. This ensures its widespread presence throughout the body from conception.
A: An oncogene is activated in some cells and a tumor suppressor deleted in others This describes specific molecular events often seen in cancer development, not the fundamental cellular distribution characteristic of a germ-line mutation's initial presence.
B: Only some cells are affected This statement describes a somatic mutation, which arises post-conception in a subset of body cells, unlike a germ-line mutation that is universally distributed from the zygote.
C: Two somatic mutations occur This option refers to a specific number and type of acquired changes in non-reproductive cells, which is unrelated to the pervasive nature of a single germ-line mutation inherited at conception.
Polygenic inheritance (multifactorial) disorders result from the interplay of genetic and environmental factors. All the following considered as polygenic inheritance EXCEPT
Rationale:
Hairy ear is not considered a polygenic inheritance disorder.
Hairy ear (hypertrichosis pinnae auris) is a Y-linked trait, meaning it is passed directly from father to son. This inheritance pattern is Mendelian, specifically sex-linked, and does not involve the complex interaction of multiple genes and environmental factors characteristic of polygenic inheritance. Polygenic disorders show continuous variation and are influenced by numerous genetic loci and environmental triggers, unlike this single-gene, Y-linked condition.
A: cleft lip and palate Cleft lip and palate arises from the combined influence of multiple susceptibility genes and various environmental triggers during fetal development, exemplifying multifactorial inheritance patterns.
B: spina bifida Spina bifida, a neural tube defect, results from the intricate interaction of several genetic predispositions and environmental factors like folate deficiency, aligning with polygenic disease etiology.
C: childhood asthma Childhood asthma manifests due to a complex interplay between numerous genetic variants influencing immune responses and environmental exposures such as allergens, epitomizing a multifactorial disorder.
5-month-old girl has bilateral retinoblastoma. Neither parent has a history of having had retinoblastoma. Chromosomal analysis of the patient’s stimulated peripheral blood lymphocytes is done; the photograph is of a representative karyotype. Which of the following critical events has most likely resulted from an aberration involving chromosome 13?
Rationale:
Tumor-suppressor gene loss has most likely resulted from an aberration involving chromosome 13.
Retinoblastoma develops from mutations in the RB1 gene located on chromosome 13, which encodes a critical tumor-suppressor protein. Loss of function of both RB1 alleles, often through a germline mutation followed by a second somatic hit like deletion or nondisjunction, is the genetic basis for this cancer. The aberration on chromosome 13 in this bilateral case points to the inactivation of this crucial growth-regulating gene.
A: Proto-oncogene activation Oncogenes promote cell division when activated, but retinoblastoma specifically arises from the inactivation of a tumor suppressor, not the overactivity of a growth-promoting gene.
B: Proto-oncogene amplification Increased copies of proto-oncogenes drive uncontrolled proliferation. Retin
Strictly speaking, maternal inheritance is best defined as
Rationale:
Maternal inheritance is best defined as monoparental disomy.
Monoparental disomy specifically refers to an individual inheriting both copies of a chromosome, or part of a chromosome, from only one parent. When this parent is the mother, it directly exemplifies maternal inheritance, distinct from typical Mendelian patterns. This phenomenon highlights instances where genetic material originates solely from the maternal lineage, impacting gene expression and potential disease manifestation through imprinting effects.
A: X-linked recessive X-linked recessive inheritance involves genes on the X chromosome, where males are typically more affected, but inheritance still involves both parents' contributions, not exclusively maternal origin.
B: only females are afflicted While some maternally inherited conditions might predominantly affect females, this outcome describes a phenotypic pattern, not the fundamental genetic mechanism of inheritance from a single parent.
C: only males are afflicted This describes a specific phenotypic outcome, often seen in X-linked traits affecting males more, but it does not define the strict genetic principle of inheriting all genetic material from the mother.
The Philadelphia translocation involves:
Rationale:
An exchange between chromosomes 9 and 22 is involved in the Philadelphia translocation.
The Philadelphia translocation is a specific chromosomal abnormality characterized by a reciprocal translocation between the long arms of chromosome 9 and chromosome 22. This exchange creates a fusion gene, BCR-ABL1, on the derivative chromosome 22, known as the Philadelphia chromosome. This oncogene encodes a constitutively active tyrosine kinase, a hallmark driver in chronic myeloid leukemia pathogenesis.
B: An exchange between chromosomes 8 to 14 This exchange describes the Burkitt lymphoma translocation, involving the MYC gene on chromosome 8 and immunoglobulin heavy chain genes on chromosome 14, distinct from the Philadelphia chromosome.
C: Translocation between chromosome 15 and 17 This specific translocation, t(15;17), defines acute promyelocytic leukemia, leading to the PML-RARA fusion gene, which is a different chromosomal rearrangement.
D: A fusion between chromosomes 14 and 21 This fusion is not a recognized common translocation associated with a specific leukemia or lymphoma, nor does it describe the well-known Philadelphia chromosome event.
Why are individuals with an extra chromosome 21, which causes Down syndrome, more numerous than individuals with an extra chromosome 3 or chromosome 16?
Rationale:
Extra copies of the other chromosomes are probably fatal.
Trisomies for larger chromosomes like 3 or 16 typically result in early embryonic or fetal lethality due to the severe genetic imbalance they cause. Chromosome 21 is one of the smallest human autosomes, and while an extra copy leads to Down syndrome, the less extensive gene dosage imbalance allows for survival to birth, making trisomy 21 the most common live-born autosomal trisomy.
A: There are probably more genes on chromosome 21 than on the others. Chromosome 21 is actually one of the smallest human chromosomes, containing fewer genes than the much larger chromosomes 3 or 16, which would lead to a greater imbalance.
B: Chromosome 21 is a sex chromosome and 3 and 16 are not. Chromosome 21 is an autosome, not a sex chromosome. Sex chromosomes are X and Y, and their aneuploidies have different survival patterns.
C: Down syndrome is not more common, just more serious. Down syndrome (Trisomy 21) is indeed the most common autosomal trisomy observed in live births, indicating its higher frequency compared to other trisomies.
A newborn infant is noted to have dysmorphic features. The pregnancy was complicated by breech presentation, decreased fetal movements, and polyhydramnios. The child demonstrates hypotonia, a flat face, flattened occiput, epicanthal folds, and abdominal distention. The most likely cause of this child's dysmorphology is
Rationale:
The most likely cause of this child's dysmorphology is trisomy 21.
This infant's presentation, including hypotonia, a flat face, flattened occiput, epicanthal folds, and abdominal distention, are classic phenotypic characteristics of Down syndrome. Prenatal complications like decreased fetal movements and polyhydramnios are also frequently associated with trisomy 21. This constellation of findings points strongly to this common chromosomal aneuploidy.
A: trisomy 13. Patau syndrome (trisomy 13) typically manifests with severe midline defects such as cleft lip/palate, microphthalmia, and polydactyly, features absent from this child's description.
B: trisomy 18. Edwards syndrome (trisomy 18) presents with distinct features like rocker-bottom feet, clenched hands, micrognathia, and severe growth restriction, which contrast with the described infant's presentation.
C: Edwards syndrome. Edwards syndrome, synonymous with trisomy 18, characteristically involves a prominent occiput, small jaw, and overlapping fingers, which do not align with the patient's reported symptoms.
A 6-month-old with unilateral retinoblastoma has genetic testing performed. The results of the tumor and blood analysis at the RBI locus are shown below (the photo is missing, but you don't need it anyway!). What is the likelihood that a future sibling WILL DEVELOP retinoblastoma?
Rationale:
The likelihood that a future sibling will develop retinoblastoma is 1%.
Unilateral retinoblastoma is often sporadic, meaning it results from two somatic mutations in a single retinal cell without a
Which of the following genetic changes is associated with a female whose karyotype is 46, XY?
Rationale:
SRY gene mutations (deletions, translocations, ...etc) is associated with a female whose karyotype is 46, XY.
A 46, XY karyotype typically denotes a male. However, a female phenotype with this karyotype strongly implicates issues with the SRY gene, located on the Y chromosome. SRY is pivotal for initiating testicular development. Mutations, such as deletions or translocations, render the SRY protein non-functional, preventing male differentiation and leading to gonadal dysgenesis and a female appearance despite the presence of a Y chromosome.
B: Monosomy X Monosomy X describes a 45, X karyotype, not 46, XY. This genetic configuration results in a female with only one X chromosome
The characteristic indicated by the blackened figures is probably:
Rationale:
The characteristic indicated by the blackened figures is probably Dominant.
The blackened figures represent individuals expressing the trait. Its appearance in every generation, with affected offspring consistently having at least one affected parent, strongly suggests a dominant inheritance pattern. If it were recessive, unaffected parents could produce affected offspring, and it might skip generations. This consistent intergenerational expression aligns with dominant allele manifestation.
B: Recessive This inheritance pattern typically skips generations, and unaffected parents can produce affected offspring, which is not observed here. Affected individuals would also need two copies of the allele.
C: Non-dominant This term lacks specific genetic meaning in describing inheritance patterns. Genetic traits are classified as dominant, recessive, or other specific modes, making "non-dominant" an imprecise descriptor.
D: Sex-linked recessive Sex-linked recessive traits usually show a higher incidence in males and distinct transmission rules, like affected fathers not passing it to sons, or affected mothers passing it to all sons, which isn't evident.
How many double stranded DNA molecules are in a somatic human cell that is in present G2 phase:
Rationale:
C: 92 double stranded DNA molecules are present in a somatic human cell that is in G2 phase.
A human somatic cell normally has 46 chromosomes. During the S phase, preceding G2, DNA replication occurs, duplicating each chromosome. Each replicated chromosome now consists of two sister chromatids, joined at the centromere, but still considered one chromosome. Since each chromatid contains one double-stranded DNA molecule, a cell with 46 duplicated chromosomes in G2 phase will possess 92 double-stranded DNA molecules.
A: 46 This represents the diploid chromosome number for a human somatic cell before S phase replication, or the number of chromosomes in G2, where each is duplicated but still counted as one.
B: 23 This number corresponds to the haploid chromosome count found in human gametes, not a diploid somatic cell in G2 phase, which would have double this amount of genetic material.
D: There are no double stranded DNA molecules in G2 Genetic material, specifically double-stranded DNA, is fundamentally present throughout all interphase stages, including G2, as the cell prepares for division, making this statement fundamentally incorrect.
You are asked to consult about a 2-month-old girl with hypotonia, seizures, and an elevated plasma lactate (8 mM/L, normal <2). Brain MRI shows a thin corpus callosum but no other abnormalities. You suspect pyruvate dehydrogenase deficiency. Which of the following is the most likely mode of inheritance in this infant?
Rationale:
Autosomal recessive is the most likely mode of inheritance in this infant.
Pyruvate dehydrogenase deficiency (PDHD) in females, presenting with severe symptoms like hypotonia, seizures, and elevated lactate, often