Dev. Bio Reviewer Gametogenesis PDF

**Dev. Bio Reviewer (Gametogenesis)** **Gametogenesis:** - Conversion of Germ Cells into Male and Female Gametes - The production of gametes from haploid precursor cells. **Primordial Germ Cells** - Gametes are derived from Primordial Germ Cells (PGCs) that are formed in the epiblast...

**Dev. Bio Reviewer (Gametogenesis)** **Gametogenesis:** - Conversion of Germ Cells into Male and Female Gametes - The production of gametes from haploid precursor cells. **Primordial Germ Cells** - Gametes are derived from Primordial Germ Cells (PGCs) that are formed in the epiblast during the 2nd week of embryonic development and move to the wall of the yolk sac. - At 4th week, these PGCs migrate towards the developing gonads, arriving at the end of the 5th week. **EPIBLAST** - Gives rise to all 3 germ layers, and the primordial germ cells. **Clinical Correlates:** *Teratomas* - Tumors that contain variety of tissues, such as bones, muscles, hair, gut epithelia etc. - May have arise from pluripotent stem cells. - Evidences suggests that teratomas arise from PGCs strayed from their original migratory paths, or epiblast cells forming the three germ layers during gastrulation.  **Chromosome Theory of Inheritance** - Traits of a new individual are determined by specific genes on chromosomes inherited from the father and the mother. - Humans have approx. 23,000 genes on 46 chromosomes Genes on the same chromosomes tend to be inherited together and so are known as linked genes. - Each chromosome pair is homologous, one coming from the female gamete, one from the male gamete. - 22 of the human chromosomes are autosomes, while one pair is the sex chromosomes **Sex Determination** **Primary Sex Determination** SRY Gene -- Sex-determining region of the Y chromosome -- Codes for the protein testis-determining factor (TDF) -- Transforms bipotential gonad into a testis **Bipotential to Specific Gonads** *2 precursor organs:* *1. Wolffian duct* -- differentiates into the structure of the male genital tract - Müllerian inhibiting hormone - causes the Müllerian ducts to atrophy instead of developing into the oviducts and uterus *2. Müllerian duct* -- source of the female reproductive organs  **Mitosis** One somatic cell divides giving rise to two identical daughter cells. Each daughter cell receives the complete complement of 46 chromosomes. Before mitosis, each chromosome replicates its DNA. **S Phase**  **Meiosis** Cell division that takes place in gametes to generate male and female gametes. Requires two divisions to reduce the number of chromosomes by half, producing haploid daughter cells. DNA Replication Synapsis Crossing-Over -- Chiasma In humans, at the end of meiosis I, each daughter cell will only have 23 unique chromosomes (haploid)