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Developmental biology
Study of progressive changes of cells and tissues
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Embryo
Stages from fertilization to hatching (birth)
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Larva
Stages between embryo and sexual maturity
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Vertebrate models for studies
- Xenopus laevis
- Gallus gallus
- Mus musculus
- Danio rerio
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Invertebrate models
- Drosophila melanogaster
- Caenorhabditis elegans
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Preformation
Idea that a completely formed organism grows larger during embryogenesis
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Homunculus
Tiny human believed to be in the head of each human sperm by preformationists
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Epigenesis
Idea that organs and structures are formed in stages during embryogenesis
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Cell theory
- States that cells are the basic unit of life
- 1. All organisms are made of cells
- 2. Cells arise from other cells
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Germ cells
Produce gametes
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Gametes
- Eggs and sperms
- Haploid cells formed by meiosis
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Somatic cells
Diploid cells which divide by mitosis
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Mutations
Alter DNA sequences and may alter cell phenotype
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Fertilization
Haploid gametes and their DNA join to form a diploid zygote
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Zygote
One-cell embryo, or fertilized egg
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Differentiation
Cellular specialization
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Early embryo cells
- Relatively generic
- Pluripotent
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Differential gene expression
Different genes are expressed at different times
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Animal pole
- The top of an amphibian embryo
- (Limbs, head, etc.)
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Vegetal pole
- The bottom of an amphibian embryo
- Contains large, heavy yolk particles (lipids)
- (usually turns into the guts)
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Cytoplasmic determinants
- Some embryos have distinctive regions of cytoplasm
- E.g. Tunicates have myoplasm
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Myoplasm
Region of cytoplasm that give rise to muscle cells in tunicates
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Mosaic development
- Determinants in the egg are divided into different cells, directing different fates
- Cell-autonomous
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Cell-autonomous
Inherent ability or fate in a cell (due to a determinant)
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Regulative development
- Cells sense their relative positions and differentiate based on external cues
- non-cell-autonomous
- This is usually observed
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