Protective layer around the ova. Contains receptors that recognize proteins of the sperm.
phase 1-penetration of corona radiate phase 2-binding of zona by sperm acrosome and penetration of zona by releasing acrosin. Sperm binds, oocyte membranee prevents further sperm binding. Cortical granules released which contain enzymes that destry sperm receptors.
cells within one person have different genetic makeup. some cells are normal while other are missing a chromosome
genetically different cells which came from separate zygotes that fused. 'fused fraternal twins'. Ex. is mothers who are 'genetically not the mother of their children'
functional inactivation of one X chromosome that occurs randomly. because it's random, all normal females will have roughly equal parts of two genetically different cell types. This is a type of mosaicism
zygote which is made of at least 2 cells after fertilization and is still within the zona pellucida. Goes from 2 cell phase to the morula (many cells)
process through which cells become held together by tight junctions. Inner cell mass which becomes the embryo proper and outer cell mass that forms the trophoblast form.
aka blastocyst, can grow into an entire organism and produce extra-embryonic tissues
Pluripotent stem cells
cannot grow into a whole organism, but may differentiate into cells derived from any of the 3 germ layers.
Fetus in fetu
aka inclusion twinning. Extremely rare abnormality that involves a fetus getting trapped inside its twin. Inner fetus is simply living tissue which feeds off the nutrients of the external individual as a form of parasite.
bilaminar germinal disc
amniotic sac cavity
bilaminar embryonic disc
yolk sac cavity
Stages of mitosis
Chromosomes condense. Centrioles move to opposite ends of the cell and mitotic spindle begins to form.
Nuclear membrane dissolves and the chromosomes are attached to a spindle microtubule.
Chromosomes line up along the equatorial line where they are maximally condensed (this is stage where chromosomes are typically stained for observation).
Centromeres replicate, divide, and are taken to opposite poles of the cells with the sister chromatids
Chromosomes start decondensing, spindle fibers disappear, and nuclear membrane re-forms. Cystokinesis also occurs, resulting in 2 separate, complete, and identical daughter cells.
Cellular replication that results in the formation of gametes. Diploid cells are reduced to haploid cells and have 23 chromosomes each instead of 46. This occurs in 2 stages.
"Reductive division" where diploid cells are reduced to haploid cells. Homologous chromosomes are separated into 2 daughter cells. Crossing over occurs in meiosis 1.
Recombination occurs here and this phase is divided into 5 sub-phases (leptotene, zygotene, pachytene, diplotene, and diakinesis). At leptotene, chromosomes condense. In zygotene, homologous chromosomes pair and associate along the entire length of the chromosome. Pachytene characterizes further coiling and the finished binding of chromosomes which are termed bivalent or tetrads depending on how many of the chromatids are joined. Pachytene is the phase where recombination or crossing-over takes place. In diplotene, the chromosomes begin to pull apart and chiasmata (locations of recombination) become apparent. In diakinesis, the chromosomes continue to separate and become maximally condensed.
Spindle apparatus forms and paired chromosomes align along the equator
Individual bivalents completely separate from each other, then the homologous chromosomes are drawn to opposite poles.
Haploid cells form from the cleavage of cytoplasm to create 2 non-identical daughter cells.
Proceeds similar to mitosis, except there is no DNA replication, only separation of sister chromatids to form haploid cells instead of diploid.
All cells in the mature body arise from what embryonic structure?
Most common congenital germ cell tumor. Thought to arise from embryologically multipotent cells from the Henson Node
Structure: Acts as a rigid axis which the embryo develops around
Skeleton: Foundation of the vertebral column
Induction: Brings about the formation of the neural tub
Ability of a cell to give rise to all cells of an organism including embryonic and extra embryonic tissues. Self-renewable and capable of producing an entire organism. Example is a zygote
Ability of a cell to give rise to all cells of the embryo (and subsequently all adult tissues) but is unable to develop into a complete organism. Self-renewable
Ability of a cell to give rise to different cell types of a given lineage. These cells either develop into the cells they are destined to become or die as they are not self-renewable.
Embryonic stem cells
Derived from the inner cell mass of the blastocyst, they are capable of proliferating indefinitely given the proper conditions. When re-injected into an embryo they frequently become tumors, often a teratoma.
Adult stem cells
Cells in tissues that respond to demands for growth and repair. They are tissue specific cells which will not develop into radically different tissue from what they are programmed to.
Example of variable expressivity. Caused by mutations in collagen and marked by blue sclera, deafness, and very fragile bones (easily fractured). Patients may present with all of these or only one.
Transcription factor. 39 genes on 4 chromosomes in 4 clusters. 13 paralogous groups. Play a major role in the craniocaudal segmentation. Arranged from 3' to 5' with 3' occurring early and 5' occurring later. Major regulator is Retinoic Acid and mutations are typically related to the vertebra and ribs.
9 members. Important in embryonic growth and post-birth functions. Heavily involved with CNS, retina, inner ear, and pancreas. Aniridia (lack of an iris) is an example.
Involved in formation of almost every body segment. Absence of these can lead to headless mammalian embryos.
6 members. Involved in jaw and inner ear morphogenesis.
6 types in humans. Pre-natally inhibit cell differentiation, post-natally maintain tissues' proliferative capacity. Involved in epithelial-mesenchymal interactions in face and limbs
T-box (tbx) gene family
100 members, 18 in humans. Important in mesodermal germ development and in specifying which limbs are forelimbs vs. hind limbs.
Helix-loop-helix transcription factors
Generally dimeric and commonly regulate myogenesis (formation of muscle tissue).
Forkhead (fox) gene family
Regulate the expression of genes involved in cell growth, proliferation, and longevity. Highly associated with heritable speech and language disorders. Defining feature is the 'winged helix'.
Regulate myogenesis and implicated in tooth, bone, and cartilage development. Deficiency may result in skeletal growth retardation and is a risk factor for osteoporosis. Includes Sox genes.
Mutation in the SOX9 gene. Affects skeletal development, reproductive, and respiratory systems and infants have short legs, dislocated hips, under-developed shoulder blades, 11 rib pairs, and club-feet, ambiguous genitalia and larygeotracheal malacia
Plays a role in kidney and gonadal development. The Wilms' tumor suppressor gene
Transforming growth factor. Wide variety of roles in embryogenesis and postnatal life. BMPs part of this family. BMP4 presence in ectoderms causes it to become epidermis and absence of BMP4 causes ectoderm to become neural plate
Fibroblast Growth Factors
22 members with 100s of isoforms. Roles in angiogenesis, wound healing, embryonic development, and endocrine signaling pathways.
Desert, Indian, and Sonic hedgehogs. SHH most important, bound to cholesterol then secreted. Binds to Patched which binds to smoothened. Plays major roles in organogenesis, facial and limb patterning and organization of the brain (think about symmetry). IHH is involved in chondrocyte differentiation. DHH defects associated with partial gonadal dysgenesis.
18 members which have a massive range of affects. Bind to frizzled receptors and LRP families.
Metabolite of vitamin A that acts through HOX genes to control anterior/posterior patterning and positioning. Also a powerful teratogen.
Code for proteins that help regulate cell growth and differentiation and are involved with signal transduction and mitogenic signaling. Upon activation, they become tumor-inducing agents called oncogenes.
Tumor Suppressor genes
Normally function to limit frequency cell division. Recessive loss of function leads to uncontrolled cell division
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