Germ Cells & Early Development
During the second week, these cells form in the epiblast and later migrate through the primitive streak during gastrulation.
What are primordial germ cells (PGCs)?
This process occurs during prophase I when homologous chromosomes pair precisely along their lengths.
What is synapsis?
A newborn has 47,XX,+21 and displays characteristic facial features, hypotonia, and congenital heart disease. This chromosomal disorder is most likely this.
What is Down syndrome (trisomy 21)?
An infant has a characteristic cat-like cry, microcephaly, intellectual disability, and congenital heart disease. This syndrome results from deletion of the short arm of chromosome 5.
What is Cri-du-chat syndrome?
A mutation occurs during embryonic development in a somatic cell, producing an individual with two or more genetically distinct populations of cells.
What is mosaicism?
During the fourth week, primordial germ cells begin migrating from the yolk sac toward these developing reproductive structures.
What are gonads?
The exchange of chromatid segments between paired homologous chromosomes during meiosis I is called this.
What is crossing over?
This syndrome is characterized by a 47,XXY karyotype and commonly presents in males with sterility, testicular atrophy, and gynecomastia.
What is Klinefelter syndrome?
A child has intellectual disability, absent speech, poor motor development, and episodes of inappropriate laughter due to a microdeletion at 15q11–15q13 on the chromosome inherited from the mother.
What is Angelman syndrome?
These cells begin meiosis I during fetal development, arrest in the diplotene stage of prophase I, and remain arrested until puberty.
What are primary oocytes?
This process includes meiosis to reduce chromosome number and cytodifferentiation to complete germ-cell maturation.
What is gametogenesis?
This X-shaped structure temporarily forms at the site where homologous chromosomes exchange genetic material.
What is a chiasma?
A female infant has a 45,X karyotype, short stature, gonadal dysgenesis, and a webbed neck. This is the only complete monosomy compatible with life.
What is Turner syndrome?
A child has hypotonia, obesity, intellectual disability, hypogonadism, and undescended testes due to a 15q11–15q13 microdeletion on the chromosome inherited from the father.
What is Prader-Willi syndrome?
Shortly before ovulation, an LH surge causes completion of meiosis I. This produces a large cell containing most of the cytoplasm and a much smaller cell with little cytoplasm. What are these two cells?
What are the secondary oocyte and first polar body?
A tumor containing tissues such as bone, hair, muscle, and gut epithelium may arise from pluripotent cells capable of differentiating into derivatives of all three germ layers.
What is a teratoma?
A primary spermatocyte undergoing meiosis ultimately produces four mature cells, whereas a primary oocyte produces one mature gamete and three cells of this type.
What are polar bodies?
A newborn has severe intellectual disability, congenital heart defects, low-set ears, flexed fingers, and multiple skeletal abnormalities. The karyotype shows an extra copy of chromosome 18.
What is trisomy 18 (Edwards syndrome)?
This technique uses fluorescent DNA probes that hybridize to specific chromosomes or genetic loci and is particularly useful for detecting microdeletions such as those responsible for contiguous gene syndromes.
What is fluorescence in situ hybridization (FISH)?
The human female gamete is arrested at this stage approximately 3 hours before ovulation and completes this meiotic division only if fertilization occurs.
What is metaphase II?
A patient has a chromosomal rearrangement in which two chromosomes exchange segments, but no critical genetic material is lost. The patient has a normal phenotype but is at increased risk of producing abnormal gametes. What type of rearrangement is this?
What is a balanced translocation?
A spermatocyte completes meiosis normally, but homologous chromosomes fail to separate during meiosis I. One resulting cell receives 24 chromosomes and the other receives 22. This error is called this.
What is nondisjunction?
A newborn has holoprosencephaly, cleft lip and palate, microphthalmia, and congenital heart defects. More than 90% of affected infants die during the first year. Which chromosomal abnormality is most likely?
What is trisomy 13 (Patau syndrome)?
A male patient has intellectual disability, large ears, a prominent jaw, and large testes. Molecular testing reveals more than 200 CGG repeats in the promoter region of a gene on Xq27.
What is Fragile X syndrome?
During this final stage of sperm development, spermatids develop an acrosome, condense their nuclei, form a tail, and shed most of their cytoplasm.
What is spermiogenesis?