Developmental Biology - Prelims Trans PDF

INTRODUCTION D. Mathematical Modelling Fields of Embryology - the study of developmental A. Comparative Embryology processes using equations. - the study of anatomical...

INTRODUCTION D. Mathematical Modelling Fields of Embryology - the study of developmental A. Comparative Embryology processes using equations. - the study of anatomical Isometric Growth changes during development among different organisms. - maintains equal proportion - comparison of modes of and uniform growth all reproduction. throughout the ontogeny o ovipary(egg) (e.g. horns). o vivipary(live) o ovovivipary(egg+live) Allometric Growth Laws of Von Baer - unequal growth throughout the development process 1. General features appear (e.g. humans). earlier, specialized features appear later in development. History of Embryology 2. Specialized features arise from less general and general Aristotle – the first embryologist features. 3. Embryos do not pass through PREFORMATIONISM – organism is adult stages of lower animals. preformed, and a miniature version is 4. Higher embryos are not lower housed within the sperm or the egg. animals but only early embryos. 1. Jan Swammerdam B. Evolutionary Embryology (insect development) 2. Marcelo Malpighi - how evolution affects (early chicken embryo structures development down the line. and organ development) - embryos may show 3. Nicolaas Hartsoeker evolutionary relationship (screw-barrel microscope and and can be used for spermatoids) taxonomic classification. 4. Charles Bonnet - evolutionary structures. (ovist) o homologous (common descent) EPIGENESIS – organisms develop by o analogous undergoing different stages of (common function) ontogeny. C. Teratology & Medical Embryology 1. William Harvey (blood circulation and the Essay - study of birth defects on the Generation of Animals) - study of malformations 2. Pierre Maupertuis o gene mutations (embryos goes through different o aneuploidy stages of development) o translocation 3. Thomas Morgan - study of disruptions caused (cytoplasmic determinants) by exogenous factors. 4. Edmund Wilson (nuclear determinants) EXAMPLES 5. Waldeyer 1. Piebaldism (tonsillar ring) 2. Phocomelia 6. Wilhelm His (microtome, paraffin histology, serial sectioning, and 3D models)  History of Embryology Female Reproductive System Spemann’s Theory of Organizers - egg protoplasm gives rise to specific structures. - these organizers play an important role in embryonic cell and tissue development. Weismann’s Theory of Germplasm - germ cells give rise to gonads and contains determinants necessary for later development. ovaries → fimbriae of the fallopian tube → ampulla of the fallopian tube → uterus → cervix → vaginal canal Spermatogenesis GAMETOGENESIS - spermatogenesis is the production Reproductive System of mature sperm cells (spermatozoa) within the seminiferous tubules of Male Reproductive System the testis. testis → epididymis → ductus deferens → ejaculatory duct → prostate gland + seminal vesicle → prostatic urethra → membranous urethra + bulbourethral/Cowper’s gland → penile urethra  Spermatogenesis Oogenesis 1. spermatogonium (2n) Type A – stem cells that undergo mitosis to produce more spermatogonium. Type B – precursors for spermatocytes. 2. primary spermatocyte (2n) - undergoes meiosis I to produce two secondary spermatocytes. 3. secondary spermatocyte (n) - undergoes meiosis II to produce - oogenesis is the production of four spermatids. mature egg cells (ova) within the ovary. 4. spermatids (n) - attached by cytoplasmic bridges. - undergoes spermiogenesis where elongation occurs. - acrosomal cap forms from the Golgi apparatus, flagellum forms from the centrioles, and mitochondria multiplies and migrates to the 1. oogonium (2n) midpiece. - Sertoli cells also dispose the - undergoes mitosis during fetal excess cytoplasm. development, wherein all ova present post-puberty are produced during this 5. spermatozoa (n) stage. - halts at prophase I until puberty - undergoes spermiation where it is and goes through a dormancy period released from Sertoli cells into the called the dictyate phase. lumen of the seminiferous tubules. - fertile human males ejaculates 2. primary oocyte (2n) twenty million sperm per milliliter (follicular phase) and an eighty-percent composition of morphologically normal sperm cells. - undergoes meiosis I to produce a secondary oocyte. 3. secondary oocyte (n) SEX DETERMINATION (ovulatory phase and menstrual phase) Introduction - halts at metaphase II until - sex determination is a biological fertilization is completed. system in determining the development - if fertilization does not occur, it of sexual characteristics of an is shed during menstruation. organism. - most organisms have two sexes 4. ootid (n) although hermaphroditism can be possible as well as parthenogenesis. - product of the secondary oocyte that has undergone meiosis II which Structural Determination will further mature into an ovum. A. Primary Sexual Differentiation 5. ovum (n) - structures relating to the gonads. B. Secondary Sexual Differentiation - structures relating to appearance that can appear during sexual maturity. Introduction to Chromosomes - mature egg cell ready to undergo 1. H. Henking fertilization with the sperm cell. - discovered the X-body which led to the discovery of sex chromosomes. 2. C.E. McClung - discovered that the X-body is important for sex determination. 3. E.B. Wilson - discovered an unpaired chromosome in Protenor which they called the X chromosome. 4. N. Stevens. - discovered the Y chromosome. luteinizing hormone (triggers ovulation) follicle-stimulating hormone (triggers the growth of eggs) estrogen (helps in ovulation and endometrial thickening) progesterone (promotes endometrial thickening and Central Histone – H8 implantation of the egg) Linker Histones – H1 and H5 Nucleosomes – DNA and histones  CHROMOSOMAL LOCATION Female Heterogamety - sex determination depends on the difference in the female’s homologous chromosome. CHROMOSOMAL STRUCTURE Haplodiploidy System CHROMOSOMAL FUNCTION - sets of chromosomes determines the male or female sex. - haploids are male and diploids are Chromosomal Determination female. Male Heterogamety Genic Sex Determination Genic Balance/Ratio System - sex determination is based on the ratio between X chromosomes and haploid autosomes, wherein: 𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑋 𝑐ℎ𝑟𝑜𝑚𝑜𝑠𝑜𝑚𝑒𝑠 - sex determination depends on the 𝑠𝑒𝑥 = difference in the male’s homologous ℎ𝑎𝑝𝑙𝑜𝑖𝑑 𝑠𝑒𝑡 𝑜𝑓 𝑎𝑢𝑡𝑜𝑠𝑜𝑚𝑒𝑠 chromosome. 1.00 = female 0.50 = male >1.00 = metafemale