Gametogenesis I and II - Human Embryology (Lecture Notes)

Vocabulary flashcards covering primordial germ cells, gametogenesis, meiosis, oogenesis, spermatogenesis, follicle development, ovulation, fertilization-related structures, and Down syndrome concepts.

Primordial germ cells (PGCs)

A population of cells that arise in the wall of the yolk sac, migrate to the developing gonad, and later become oogonia in ovaries or spermatogonia in testes.

oogonia

Diploid germ cells in the fetal ovary that proliferate mitotically and enter meiosis to form primary oocytes.

spermatogonia

Diploid germ cells in the testis that proliferate mitotically and differentiate toward primary spermatocytes.

mitosis

A cell division process that results in two genetically identical diploid daughter cells; used by PGCs, oogonia, and spermatogonia before meiosis.

meiosis

A two-part cell division process that reduces chromosome number from diploid to haploid and includes genetic recombination.

primary oocyte

Diploid cell that enters meiosis I during fetal development and is arrested in prophase I until ovulation.

secondary oocyte

Product of meiosis I; haploid cell that is arrested at metaphase II until fertilization.

polar body (oogenesis)

Small haploid cell produced during oogenesis that receives little cytoplasm; may be expelled during meiosis.

oogenesis

Development of female gametes in the ovaries, characterized by asymmetric divisions and long arrest periods.

spermatogenesis

Development of male gametes (sperm) in the testes, a continuous process after puberty with many sperm produced.

ovulation

Mid-cycle release of the secondary oocyte from the ovary, accompanied by the zona pellucida and corona radiata.

zona pellucida

Glycoprotein layer surrounding the oocyte that binds sperm during fertilization.

cumulus oophorus

Cluster of granulosa cells that surrounds the oocyte and anchors it to the follicle.

corona radiata

Layer of granulosa cells still attached to the oocyte after ovulation, just outside the zona pellucida.

primordial follicle

The earliest follicle, containing a primary oocyte with flattened follicular cells.

growing follicle

Follicle in which granulosa cells proliferate and the zona pellucida begins to form.

primary follicle

Follicle with a developing stratified layer of granulosa cells around the oocyte and a defined zona pellucida.

Graafian (mature) follicle

Fully developed secondary follicle with a large antrum and many granulosa cells preparing for ovulation.

theca interna

Inner layer of theca cells that produces androgens which are converted to estrogens by granulosa cells.

theca externa

Outer connective tissue layer surrounding the follicle.

antrum

Fluid-filled cavity within antral/mature ovarian follicles.

corpus luteum

Temporary endocrine structure formed from the ruptured follicle after ovulation; secretes progesterone.

nondisjunction

Failure of homologous chromosomes or sister chromatids to separate properly during meiosis, leading to aneuploid gametes.

trisomy 21 (Down syndrome)

A chromosomal disorder where there are three copies of chromosome 21 in cells, causing characteristic features and risks.

monosomy

Presence of a single copy of a chromosome in a cell; often lethal for embryos.

karyotype

A visual display of an individual’s chromosomes arranged by size and shape for analysis.

crossover (chiasma)

Exchange of genetic material between homologous chromosomes during meiosis I, visible as a chiasma.

synapsis

Pairing of homologous chromosomes during prophase I of meiosis.

diploid

Cells containing two complete sets of chromosomes (2n).

haploid

Cells containing a single set of chromosomes (n); typical of gametes.

dyad (double-structured chromosome)

A chromosome composed of two sister chromatids held at the centromere (product of DNA replication before separation).

primary spermatocyte

Diploid cell that undergoes meiosis I to form secondary spermatocytes during spermatogenesis.

secondary spermatocyte

Haploid cell produced by meiosis I that immediately enters meiosis II to form spermatids.

spermatid

The haploid product of meiosis II that matures into a spermatozoon during spermiogenesis.

spermatozoon (sperm)

Mature male gamete capable of fertilizing an oocyte.

spermiogenesis

Process by which spermatids mature into fully formed spermatozoa, including acrosome and flagellum development.

Sertoli cells

Supportive somatic cells within the seminiferous tubules that nurture developing germ cells.

acrosome

Glycoprotein cap on the head of the sperm that contains enzymes essential for fertilization.

midpiece (mitochondria)

Sperm region rich in mitochondria that powers propulsion of the flagellum.

flagellum

Tail-like structure that enables sperm motility.

Type A dark spermatogonia

Stem-cell-like spermatogonia thought to maintain the germ cell line; reserve pool.

Type A pale spermatogonia

Spermatogonia that progress toward differentiation and eventually enter meiosis.

Type B spermatogonia

Spermatogonia that enter mitosis/meiosis to form primary spermatocytes.

fimbriae

Finger-like projections of the oviduct that help capture the oocyte released at ovulation.

fimbrial linkage to ovary

Anatomic relationship where fimbriae guide the oocyte from the ovary into the fallopian tube.

corpus luteum degeneration

Regressive phase if fertilization does not occur; progesterone production falls.

mitotic divisions in gametogenesis

Initial proliferation phase in germ cells before meiosis begins in both sexes.

first meiotic division

Meiosis I; homologous chromosomes separate, producing two haploid cells with duplicated chromosomes.

second meiotic division

Meiosis II; sister chromatids separate, yielding four unique haploid gametes.

trisomy 21 risk and maternal age

Incidence of Down syndrome increases with maternal age due to higher nondisjunction risk.

Down syndrome features

Characterized by short stature, characteristic facial features, hypotonia, cognitive challenges, and potential congenital defects.

Translocation trisomy 21

A Down syndrome variant caused by a translocation, not a full extra chromosome.

Mosaicism

Presence of two or more genetically distinct cell lines within an individual, including some with trisomy 21.