Prenatal Development Flashcards
What are chordates?
All animals with spinal cords
What do a majority of these chordates have?
A backbone (vertebral column)
What does biodiversity mean?
The number of different kinds of species in each group of living animals
Describe the species biodiversity
Other insects and beetles are major groups.
No. of chordates are very small
Estimates of how many species on earth = 5-5- million
Describe the similarities of development across species
Diverse species e.g mice + humans = similar gestational processes
all species develop from single eggs, which diversify into complex organisms w/ brains, eyes and mouths.
Who suggested the recapitulation theory?
Suggested by Haeckel when reporting the similarity of forms of early embryos of a variety of species
What is the recapitulation theory?
Popularised in the 19th century. This theory suggests that embryonic development (ontogeny) repeats the evolutionary history of an animal’s ancestors (phylogeny).
Drawing of embryos supported this theory.
How does the recapitulation relate to humans?
Human development occurs in the form of adult animals lower down the evolutionary scale. Animals would stop developing at the appropriate time for their species.
What is a problem with the recapitulation theory?
Technological advancement (photography developing in the late 19th century), shows that this view is not correct.
What can be said learnt from the recapitulation debate?
- Prior beliefs = influence perception
- How reliant science enquiry is on technology
Name 3 examples of improvements in molecular biology that caused an increased understanding of development
1950s - invention of the microscope
1695 - performation theory of development
Late 19th century - improvement in optics
What is Hartoseker’s Performation theory?
Nicolaas Hartoseker saw a tiny human inside a sperm cell when using a more powerful microscope. This popularised the idea that the womb was an oven where tiny humans expanded.
What did the improvement in optics lead to?
Led to embryonic growth now understood to involve substantial differentiation.
What did Aristotle suggested about prenatal development that was popularised around 384-322 B.C?
Suggested a chain of being (Scala naturae) where there was higher and lower life forms - a hierarchy. This idea is widespread outside science.
What are the problems of Aristotle’s suggestions?
Theory suggested evolutionary change is a directional process = false
Misconception that humans are at the top (the most perfect)
What are the three stages of prenatal development?
- The Geminal Period = conception to implantation in the uterine wall
- The Period of the Embryo = implantation to ~2mths
- The Period of the Foetus = 2mths to birth
What is the Geminal Period?
- Sperm and egg cell fuse = zygote (fallopian tube)
- Zygote moves to uterus
- In first 4 days, Zygote cells multiply = mass of cells - morula (daughter cells look the same as parent cells)
- Day 5 = turns into a blastocyst (earliest example of physical differentiation of tissue in the prenatal development )
- Day 8-9 = implantation of blastocyst on the uterine wall making a hypoblast
What is the Period of the Embryo?
- Blastocyst = 3 layers of major tissues (ectoderm, mesoderm and endoderm)
- Post implantation = embryo has identifiable diff. tissues e.g heart, eye, cartilaginous scaffolds but not bones
- One month post-implantation = individual toes, fingers is apparent and gut bulge