Lecture 1 – Early embryo development:
Drosophila – the animal geneticist’s model organism:
• Easy to breed
• High fecundity
• Tolerant of diverse conditions
• Fast lifecycle. Lab flies 26 days (female) and 33 dyas (male)
• Sequenced genome
Drosophila lifecycle:
• The female fruit fly, about 3
mm in length, will lay
between 750 and 1,500 eggs
in her lifetime.
• The life cycle of the fruit fly
only takes about 12 days to
complete at room
temperature (25°C).
• After the egg (at a mere half
a millimeter in length) is
fertilized, the embryo
emerges in ~24 hours.
• The embryo undergoes
successive molts to become
the first, second, and
third instar larva.
• The larval stages are characterized by consumption of food and resulting
growth, followed by the quiescent pupal stage, during which there is a
dramatic reorganization of the body plan (metamorphosis) followed by the
emergence of the adult fly.
• We will focus only on the early stages of embryo development in these
lectures.
Early embryo development in Drosophila:
• Very well understood because of powerful genetic approaches (using
mutants e.g. flies where a gene cannot be expressed).
• Following fertilization, zygotic nuclei undergo successive mitotic divisions, but
without cell division.
• 12 nuclear division results in a single cell with around 6000 nuclei. Known as
the Syncitial stage and the cell is called a Syncytium. Without this stage none
of the embryo patterning could take place.
• Maternal gene mRNAs are initially laid down in a polar arrangement in the
oocyte (egg) as it forms in the ovary.
1
Drosophila – the animal geneticist’s model organism:
• Easy to breed
• High fecundity
• Tolerant of diverse conditions
• Fast lifecycle. Lab flies 26 days (female) and 33 dyas (male)
• Sequenced genome
Drosophila lifecycle:
• The female fruit fly, about 3
mm in length, will lay
between 750 and 1,500 eggs
in her lifetime.
• The life cycle of the fruit fly
only takes about 12 days to
complete at room
temperature (25°C).
• After the egg (at a mere half
a millimeter in length) is
fertilized, the embryo
emerges in ~24 hours.
• The embryo undergoes
successive molts to become
the first, second, and
third instar larva.
• The larval stages are characterized by consumption of food and resulting
growth, followed by the quiescent pupal stage, during which there is a
dramatic reorganization of the body plan (metamorphosis) followed by the
emergence of the adult fly.
• We will focus only on the early stages of embryo development in these
lectures.
Early embryo development in Drosophila:
• Very well understood because of powerful genetic approaches (using
mutants e.g. flies where a gene cannot be expressed).
• Following fertilization, zygotic nuclei undergo successive mitotic divisions, but
without cell division.
• 12 nuclear division results in a single cell with around 6000 nuclei. Known as
the Syncitial stage and the cell is called a Syncytium. Without this stage none
of the embryo patterning could take place.
• Maternal gene mRNAs are initially laid down in a polar arrangement in the
oocyte (egg) as it forms in the ovary.
1
