Developmental Biology

1. Introductions
Name: Moseki P
Office: Block 235/205
Course layout: Animal development (7 wks) and plant development (7
wks).
Minimum CA of 40%: for those who started in 2022 and beyond
CA:EXAM ratio: 40:60 (20% of CA for animal and 20% for plant)
Lab session: labs on Thursdays 3-6pm (mandatory to attend)
We are going to have 1 continues lab (Do not to miss any session)

2. Bio 306
Developmental Biology
Animal development sessions

3. The basis Kingdom Animalia
Classification
Levels of organization
• single cell and multicellular
Body Symmetry
• radial and bilateral
Primary layers
• diploblastic or triploblastic
Presence of coelom
Body segmentation
The notochord

6. Animal Development
• Progressive change in the life of an animal
• Always an order
• Current form different from previous
• Two terms to consider
• Ontogeny
• The study of the developmental events that occur during
the whole lifespan of an organism
• Phylogeny
• The study of the evolutionary history of a particular
species or a group of related organisms.

7. Principles of Animal Development
•Development
•Where multicellular organisms grow and increase in
organisation and complexity
•Three principle mechanisms:
•Individual cells multiply
•Some of their daughter cells differentiate, or
specialize in both structure and function
•As they differentiate, groups of cells move and
become organized into multicellular structures.

8. From identical to differentiated
• All of the cells of an individual animal’s body are
genetically identical in an animal’s body
• How can they differentiate into different structures
with distinct functions?
• The solution is that different genes in different places
and at different times in an animal’s body, are active.

9. Indirect and direct development
• Baby mammals and reptiles are miniature versions of
the adults of their species, undergoing direct
development
• The majority of animals species undergo indirect
development - the newborn has a very different body
structure than the adult

10. Indirect development
• Animals undergo a radical change in body form
oE.g., Amphibians - frogs and toads, most invertebrates • Females
produce huge numbers of eggs, each containing yolk
oThe yolk nourishes the developing embryo until it hatches into a
small, sexually immature feeding stage called a larva
oParents provide these vulnerable offspring with neither food or
protection from predators, most die in their larval stage
oAfter feeding for weeks to years, a handful of survivors undergo a
revolution in body form - metamorphosis, and become sexually
mature adults

11. Direct development
• Newborn animals resemble miniature adults
oSnails and fish, all mammals, reptiles (including birds),
undergo direct development
oAs the young animal matures, it may grow bigger, but
does not fundamentally change its body form

12. Animal
reproduction
• Individual organisms do not live
forever
• Continuity of a species relies on
individuals reproduction
• Two types of reproduction:
asexual and sexual reproduction

13. Asexual reproduction
•Common in small animals with a simple body
form
•Starfish
•Hydra
•Flatworm
•Cells divide by mitosis
•Young ones are genetically identical to parents

14. Forms of asexual reproduction
Binary fission
• Unicellular organisms divides into identical cells, e.g., amoeba
Fragmentation
• Pieces of one organism develop into mature clonal organism,
e.g., start fish
• The original organism also regenerates the piece that broke off
Budding
• Reproduction from a protrusion, e.g., hydra

15. Forms of asexual reproduction
Parthenogenesis
Offspring comes off an unfertilised egg
oMainly due to unavailability of partners
oAn immediate threat to female's life
oOccurs in bees, grasshoppers and lizards such a
komodo dragon

16. Forms of asexual reproduction

17. Advantages disadvantages of
asexual reproduction
Advantages
• No need to spend time and energy finding a mate
• No need to use energy resources producing eggs and sperm that
potentially would never be used
Disadvantages
• Lack of variation within the population means the species is less likely
to survive environmental challenges

18. Sexual
reproduction
• Reproduction in high animals
• Involves the fusion of haploid
male and female gametes to
form a diploid zygote
• Allows for the reshuffling of
genetic material

19. Sexual reproduction
• The cells of multicellular organisms are divided into two
broad catergories:
oGerm cells- give rise to gametes
oSomatic cells- all cells of the body except germ cells.

20. Sexual reproduction
• Meiotic divisions of the germ cells to produce
haploid gametes (ova and sperm) in a process
called gametogenesis
• The ova and sperm fuse to form a diploid
zygote (fertilization)
• Zygote then divides through mitosis to produce
large number of cells that differenciate to form
various tissues that make an individual
Sexual
reproduction
involves the
following
processes:

21. Sexual reproduction
Sexual reproduction usually involve two parents but they are
exceptions:
• Some worms such as tapeworms are hermaphrodites- they
have both male and female reproductive organs
• Hermaphrodites do not self fertilise as a first option but
when they do they produce a genetically different offspring.

22. Advantages and disadvantages of
sexual reproduction
Advantages
• Brings about genetic diversity that allows species survival in
changing environmental conditions (adaptation).
Disadvantages
• Production of germ cells requires energy
• Organism need to find time to mate
• Some reproductive behaviours may attract predators
• Reproduction in some species leads to deadly competition between
males

23. Sexual reproduction
Take home assignment
• Differentiate between primary and secondary sex organs
(2 marks)
• Differentiate between totipotent, pluripotent and
multipotent cells (6 marks)
• What is the difference between parthenogenesis and
hermaphroditism? (4 marks)
• With the help of examples describe direct and indirect
development (6 marks)