Presentation on theme: "Haploid vs Diploid Review"— Presentation transcript:
1Haploid vs Diploid Review Humans have 46 chromosomes23 from mom, 23 from dadWhen it comes to chromosomes, humans have two types of cellsSomaticDiploid (contains a two copies of each chromosome)Body cells (everything but ovary, testes, sperm and egg)Germ cellsOvary and testes start diploid and produce haploid sperm and eggSperm and egg Haploid (contain one cope of each chromosome)
2FertilizationSperm’s 23 chromosomes (haploid) + Egg’s 23 chromosomes (haploid) = 46 (diploid)Sperm + Egg = ZygoteOvary (2n) cells in females produce eggs (n)Testes (2n) cells in males produce sperm (n)
3EmbryologyOnce the zygote starts dividing, it’s called an embryoStudy of early development of an embryo
4Fertilization Only ONE sperm is allowed to enter the egg Fast block - electrical charge in egg plasma membrane prevents polyspermy (more then sperm entering)Slow block - depolarization of egg plasma membrane due to Ca++ release (the egg is no longer susceptible to more fertilization)
5Cleavage partitions the cytoplasm of one large cell EmbryologyCleavage partitions the cytoplasm of one large cellInto many smaller cells called blastomeres(a)Fertilized egg. Shown here is thezygote shortly before the firstcleavage division, surroundedby the fertilization envelope.The nucleus is visible in thecenter.Four-cell stage. Remnants of themitotic spindle can be seenbetween the two cells that havejust completed the secondcleavage division.(b)Morula. After further cleavagedivisions, the embryo is amulticellular ball that is stillsurrounded by the fertilizationenvelope. The blastocoel cavityhas begun to form.(c)Blastula. A single layer of cellssurrounds a large blastocoelcavity. Although not visible here,the fertilization envelope is stillpresent; the embryo will soonhatch from it and begin swimming.(d)Figure 47.7a–d
6CleveageCleavage is a series of rapid mitotic divisions (without cell growth)The two-celled zygote divides repeatedly until a ball of 32 cells is formedThis is the morula - 32 cells
7The morphogenetic process called gastrulation Rearranges the cells of a blastula into a three-layered embryo, called a gastrula, that has a primitive gutGastrulation starts 7 – 10 days after fertilization!!!!!!!!
8Gastrulation The three layers produced by gastrulation The ectoderm Are called embryonic germ layersThe ectodermForms the outer layer of the gastrulaThe endodermLines the embryonic digestive tractThe mesodermPartly fills the space between the endoderm and ectoderm
9Digestive tube (endoderm) Gastrulation in a sea urchinProduces an embryo with a primitive gut and three germ layersFigure 47.11Digestive tube (endoderm)KeyFuture ectodermFuture mesodermFuture endodermBlastocoelMesenchyme cellsVegetal plateAnimal poleVegetal poleFilopodia pulling archenteron tipArchenteronBlastopore50 µmMouthEctodermMesenchyme: (mesoderm forms future skeleton)Anus (from blastopore)The blastula consists of a single layer of ciliated cells surrounding theblastocoel. Gastrulation begins with the migration of mesenchyme cellsfrom the vegetal pole into the blastocoel.12The vegetal plate invaginates (buckles inward). Mesenchyme cellsmigrate throughout the blastocoel.Endoderm cells form the archenteron (future digestive tube). Newmesenchyme cells at the tip of the tube begin to send out thinextensions (filopodia) toward the ectoderm cells of the blastocoelwall (inset, LM).3Contraction of these filopodia then drags the archenteron acrossthe blastocoel.4Fusion of the archenteron with the blastocoel wall completesformation of the digestive tube with a mouth and an anus. Thegastrula has three germ layers and is covered with cilia, whichfunction in swimming and feeding.5
10The mechanics of gastrulation in a frog Are more complicated than in a sea urchinFigure 47.12SURFACE VIEWCROSS SECTIONAnimal poleBlastocoelDorsal lipof blastoporeVegetal poleBlastulashrinkingArchenteronremnantEctodermMesodermEndodermGastrulaYolk plugKeyFuture ectodermFuture mesodermFuture endodermGastrulation begins when a small indented crease,the dorsal lip of the blastopore, appears on oneside of the blastula. The crease is formed by cellschanging shape and pushing inward from thesurface (invagination). Additional cells then rollinward over the dorsal lip (involution) and move intothe interior, where they will form endoderm andmesoderm. Meanwhile, cells of the animal pole, thefuture ectoderm, change shape and begin spreadingover the outer surface.The blastopore lip grows on both sides of theembryo, as more cells invaginate. When the sidesof the lip meet, the blastopore forms a circle thatbecomes smaller as ectoderm spreads downwardover the surface. Internally, continued involutionexpands the endoderm and mesoderm, and thearchenteron begins to form; as a result, theblastocoel becomes smaller.123Late in gastrulation, the endoderm-lined archenteronhas completely replaced the blastocoel and thethree germ layers are in place. The circular blastoporesurrounds a plug of yolk-filled cells.
11Many different structures GastrulationMany different structuresAre derived from the three embryonic germ layers during organogenesisFigure 47.16ECTODERMMESODERMENDODERM• Epidermis of skin and its derivatives (including sweat glands, hair follicles)• Epithelial lining of mouth and rectum• Sense receptors in epidermis• Cornea and lens of eye• Nervous system• Adrenal medulla• Tooth enamel• Epithelium or pineal and pituitary glands• Notochord• Skeletal system• Muscular system• Muscular layer ofstomach, intestine, etc.• Excretory system• Circulatory and lymphatic systems• Reproductive system (except germ cells)• Dermis of skin• Lining of body cavity• Adrenal cortex• Epithelial lining of digestive tract• Epithelial lining of respiratory system• Lining of urethra, urinary bladder, and reproductive system• Liver• Pancreas• Thymus• Thyroid and parathyroid glands
12Classic studies using frogs GastrulationClassic studies using frogsGave indications that the lineage of cells making up the three germ layers created by gastrulation is traceable to cells in the blastulaFigure 47.23aFate map of a frog embryo. The fates of groups of cells in a frog blastula (left) weredetermined in part by marking different regions of the blastula surface with nontoxic dyesof various colors. The embryos were sectioned at later stages of development, such asthe neural tube stage shown on the right, and the locations of the dyed cells determined.Neural tube stage(transverse section)BlastulaEpidermisCentralnervoussystemNotochordMesodermEndoderm(a)
13Organogenesis in the chick OrganogensisOrganogenesis in the chickIs quite similar to that in the frogFigure 47.15a, bNeural tubeNotochordArchenteronLateral foldForm extraembryonicmembranesYOLKYolk stalkSomiteCoelomEndodermMesodermEctodermYolk sacEyeForebrainHeartBloodvesselsSomitesEarly organogenesis. The archenteron forms when lateral foldspinch the embryo away from the yolk. The embryo remains opento the yolk, attached by the yolk stalk, about midway along its length,as shown in this cross section. The notochord, neural tube, andsomites subsequently form much as they do in the frog.(a)Late organogenesis. Rudiments of mostmajor organs have already formed in thischick embryo, which is about 56 hours oldand about 2–3 mm long (LM).(b)