Pregnancy WHAT IS NORMAL, WHAT CAN GO WRONG, AND HOW CAN WE ASSIST INFERTILE COUPLES? PART 1 THIS WORK IS LICENSED UNDER A CREATIVE COMMONS ATTRIBUTION - NONCOMMERCIAL - SHAREALIKE 4 . 0 INTERNATIONAL LICENSE . When Does Pregnancy Occur? Pregnancy can occur when the oocyte (egg) is released during ovulation and sperm is present. Ideally, the sperm fertilizes the oocyte in the fallopian tubes so the developing embryo has time to mature before reaching the uterus for implantation. Fertilization can occur ectopically (in the abdomen) and also in the uterus but these do not usually result in successful pregnancies. Ultrasound of a Non-Pregnant Uterus in Rhesus Macaque Photo: Mary Zelinski, PhD, ONPRC Spermatogenesis in Males Oogenesis in Females Spermatogium- Stem cell which Oogonium may mitotically divide to form more spermatogia. Primary Primary Oocyte Spermatocyte Meiosis I Meiosis I Secondary Secondary Oocyte & Polar Spermatocytes Body-Released at ovulation Meiosis II Meiosis II- Triggered by Spermatids Sperm Entry Zygote-46 Chromosomes, Cell Differentiation 23 Each From Mature Sperm Cells Oocyte & Sperm Each sperm=23 chromosomes Drawing: Lynda Jones, MS, ONPRC How do Oocytes Develop? Primary oocyte with its Primary oocyte undergoing Secondary oocyte with first nucleus arrested at meiosis I – nucleus and polar body resulting from prophase I of meiosis I. nucleolus have disappeared. meiosis I. Clinically called Clinically called Clinically called Metaphase II (M2). Germinal Vesicle (GV). Metaphase I (M1). Photos: Dr. Mary Zelinski, PhD, ONPRC In Vitro Primary Oocyte Growth in Its Follicle Antral Follicle Just Prior to Ovulation Primary Oocyte Photos: Mary Zelinski, PhD, ONPRC Photos: David Lee, MD, OHSU; Illustrations: Joel Ito, ONPRC What Types of Genetic Errors Can Occur As Ooctyes and Sperm Develop? http://upload.wikimedia.org/wikipedia/commons/3/31/Mitotic_nondisjunction.png http://creativecommons.org/licenses/by-sa/3.0/deed.en No changes have been made. The Origin of Aneuploidy Gametes by Nondisjunction at the First or Second Meiotic Division http://upload.wikimedia.org/wikipedia/commons/b/ba/Trisomy_due_to_nondisjunction_in_maternal_mei osis_1.png http://creativecommons.org/licenses/by-sa/3.0/deed.en No changes have been made. Crossing Over in Meiosis I http://cnx.org/contents/[email protected]:57/Biology http://creativecommons.org No changes were made. Translocation Between Chromosomes 9 and 22 A metaphase cell positive for the BRC/ABL translocation (shown as green and red fused together) using FISH. https://commons.wikimedia.org/wiki/File:Bcrablmet.jpg https://en.wikipedia.org/wiki/GNU_Free_Documentation_License https://creativecommons.org/licenses/by-sa/3.0/deed.en .