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1. Define the following terms: Fertilization, cleavage, Parthenogenesis, blastula, morula, gastrula.
- Fertilization: When sperm enters egg
- Cleavage: the process of nucleus and cell division in the zygote
- Parthenogenesis: Egg that multiplies and becomes organism WITHOUT sperm (eg. Rotifers, crustaceans, insects, fishes, desert lizards, etc)
- morula: “solid” ball of cells
- blastula: “hollow” ball of cells (called a blastocyst in humans)
- Blastocoel is the empty space within the blastula (and gastrula)
- Gastrula: cells begin to invaginate and form the archenteron (embryonic gut)
- Blastophore (the invagination of the gastrula) will eventually become either the mouth or the anus
Define the following terms: gastrulation, neurulation, organogenesis, gametes, acrosomal sac, zygote
- Gastrulation: transformation of the blastula into the gastrula
- Neurulation: formation of neurons
- Organogensis: formation of organ
- Gametes: sperm and egg (only haploid cells in body)
- Acrosomal sac: layer on top of head of sperm which dissolves the outside of the egg during fertilization
- Zygote: fertilized egg
2. Define the following types of cleavage with one example: Spiral, radial, rotational, discoidal, and superficial.
- Spiral: the first two planes of cleavage are vertical and produce blastomere of equal size. The third cleavage is horizontal and blastomere are unequal. [eg. mollusk (snail, octopus) and anneleids (earthworm, leech)]
- Radial: The first two planes of cleavage are horizontal and produce equal blastomere. The third plane of cleavage is also horizontal and blastomere are unequal. [ eg. Starfish and frog.]
- Rotational: After the second cleavage one pair of blastomere comes to lie at right angles to the others. [eg. Humans.]
- Discoidal: The cleavage is restricted to a small disc at one end of the embryo (middle), the rest is yolk. [eg. Birds.]
- Superficial: Yolk is in the center and cleavage is in the outer surface. [eg. Arthropods.]
3. What are the differences between Deuterostome and Protostome animals?
- Protostomia: “mouth first” – blastophore becomes mouth. Most have spiral cleavage, are schizocoelous (coelum is formed by splitting cells), and mosaic embryo cleavage.
- Deuterostomia: “mouth second” – blastophore becomes anus. Most have radial cleavage, are entercoelous (coelum is formed by outpocketing cells), and regulative embryo cleavage.
- Note: human is schizocoelus, rotational cleavage, deuterostome
4. What are the different types of yolk, give an example of each?
- Isolecithal: small amount of yolk is approximately equal to amount of cleavage [eg. Starfish and human]
- Mesolecithal: moderate amount of yolk (more than isolethical) [eg. Frog]
- Telolecithal: huge yolk [eg. Birds]
- Centrolecithal: yolk is in center surrounded by cleavage, large amount of yolk [eg. Insects]
5. What are the three germ layers and what do they become?
- Ectoderm: (blue on models) epidermis and associated structures (hair, nails, etc), brain and nervous system
- Endoderm: (yellow on models epithelial cells of G.I. tract, glands including liver and pancreas, inner lining of respiratory tract
- Mesoderm: (red on models) notochord, outer covering of internal organs, muscles, excretory system, dermis, bones and cartilage, circulatory system (heart, blood vessels, etc)
6. What is the difference between diploblastic animal and triploblastic animal?
- Triplobastic: has 3 germ layers (ectoderm, endoderm, mesoderm) – this is the majority of animals
- Diploblastic: has 2 germ layers (ectoderm, endoderm) – these are simple animals that lack body cavities and true organs (eg. Jellyfish)
- Note: Tripoblastic animals are said to be evolved from diploblastic animals
7. What are the differences between Schizocoelous and Enterocoelous animals?
- Schizocoelous: coelum is formed by splitting cells (scattered cells)
- Entercoelous: coelum is formed by outpocketing cells
- Note: coelum is the space surrounded by mesoderm
8. What is the difference between holoblastic and meroblastic animal?
- holoblastic: The entire cell divides in the absence of large concentration of yolk (isolecithal and Mesolecithal) leads to radial, spiral, and rotational cleavage (eg starfish)
- meroblastic: Only part of the cell can divide due to the presence of large concentration of yolk (telolecithal and centrolecithal) leads to discoidal and superficial cleavage. (eg frog)
9. What is metamorphosis?
Sharp changes in embryonic development (for example, a beetle looks completely different from its pupa)
10. What are the similarities and differences between regulative and mosaic cleavage?
- Regulative: if you separate the cells of a morula and they become normal animals
- Mosaic: if you separate the cells of a morula and they become defective animals (because the cells are communicating, even at such an early stage)
11. Explain animal cloning and the term totipotent?
- totipotent: one cell can become the entire organism (egg is the only cell in the human body BUT it is haploid, so it requires a sperm OR the replacement of its haploid nucleus with the nucleus from a somatic diploid cell.
- Dolly’s cloning process: remove nucleus from an egg (n) of black headed sheep, replace nucleus with nucleus from mammary cell (2n) of white headed sheep then grow in petri dish until it becomes a blastula then implant it into the black headed sheep. When the sheep was born it was 95% identical to white headed sheep (mitochondria were different because they came from black headed sheep). This was the first clone created of a mammal.
12. Explain stem cell and multipotent?
- Multipotent (pluripotent) cells: stem cell that can drive to multiple cell types (but not ALL cell types)
- Adult stem cells: (bone marrow, fat cells) cells from body that can be cultured into specific cell-types and surgically implanted. Very difficult to achieve, but there is no risk of rejection.
- Embryonic stem cells: (cells from inner mass cells (not trophoblast) of blastocyst) that can be cultured into specific cell types. Easier process than adult stem cells BUT runs the risk of rejection because it comes from a different person.
- Note – embryonic stem cells received from fertility clinic after successful implantation from “leftovers”
13. Diagram the differentiation of the germ layers?
14. What is the differentiation of brain?
15. What is the purpose of amnion?
Amnion: a sac full of fluid that surrounds the embryo and acts as a shock absorber to protect it.
16. What is the function of amnion, allantois and chorion?
- Amnion: a sac full of fluid that surrounds the embryo and acts as a shock absorber to protect it.
- Allantois: highly vascularized area that connects with embryo to bring in nutrients and remove wastes
- Chorion: a second sac that surrounds the amnion and the allantois
- Chorioallantoic membrane: alantois and chorion merge later in development to create the chorioallantoic membrane
- Note – Amniotic eggs are found in reptiles, birds, and mammals (NOT FISH)
Main stages of embryo development in humans
Fertilization -> zygote -> morula(4d) -> blastocyst(5-7d) (called blastula in other animals) -> gastrula(8-10d) -> embryo(8 wks) -> fetus(9wks-birth)