1. Three groups of genes play important roles in genetic regulation of development in Drosophila: maternal effect genes, segmentation genes, and homeotic selector genes. 2. Maternal effect genes determine polarity in the egg and early embryo. Segmentation genes establish segment boundaries and include gap, pair-rule, and segment polarity genes. 3. Homeotic selector genes, also called hox genes, regulate development of body structures and are organized into two clusters, Antennapedia and Bithorax, that control segment identity.

1. Genetic Regulation of Development in
Drosophila
Dipali Ramesh Bane
MSc - part 2 G.N. Khalsa
College, Mumbai-19

2. Introduction
1. A fruit fly or Drosophila melanogaster is a small dipteran
approximately 3mm in measurement
2. Heavily used for research in genetics
3. Can be easily cultured and have short generation time
4. Mutants can be easily obtained
5. Lifespan is about 21 days
6. Development period varies with temperature
7. First introduced by Thomas Hunt Morgan in 1909
8. Genome can be easily manipulated

3. Life cycle
Homometabolous method
of development

4. Drosophila melanogaster
Bilateral symmetrical
body
Segments -
1. Head
2. Thorax
3. Abdomen

5. 3 Groups of genes play role in developmental
process of Drosophila
1. Maternal effect genes
2. Segmentation genes
3. Homeotic selector genes

6. 1. Maternal effect genes
1. These genes express prior to fertilisation during
oogenesis by mother
2. Polarity of egg is being determined by these
maternal effect genes
3. The product of maternal genes are maternal mRNAs
4. These are produced by two cells :
• Nurse cells
• Follicle cells
5. Product of these maternal genes help
indetermining the polarity of egg

7. Among all maternal genes 4 genes basically regulates the
anterior - posterior axis in Drosophila egg
1. Hunchback
2. Bicoid
3. Nanos
4. Caudal
Transcripts of all these four genes are synthesized by nurse cells
and follicle cells and transported to oocytes

9. Two more sets of maternal effect genes in
Drosophila
1) Torso : Generates the extremes of anterior - posterior axis
in Drosophila embryo
2) Toll : Determines the dorso - ventral axis

10. 2: Segmentation genes
1. The segmentation genes
controls the development or
small repeated regions of
body that will make a
specific body structure
2. Basically segmentation
genes setup the boundaries
of the segments in a fly
embryo during development

11. Types of segmentation genes
1. Gap genes
2. Pair rule genes
3. Segment polarity genes

12. 1) Gap genes
1. Expressed early in development in broad regions
2. These genes generally defines the head , thorax and
abdomen region
3. These genes encodes the transcription factors that
controls the expression of other genes
4. If there is mutation in these genes that segment will be
absent from the developing embryo and a gap will be
there

13. Gap genes in Drosophila
1. Knirps
2. Kruppel
3. Giant
4. Tailless
5. Hunchback

14. 2) Pair rule genes
1. The protein product of the gap genes activates the
transcription of pair rule genes
2. It involves in the development of the segmented
embryos of insect

15. Examples of pair rule genes
1. Even - skipped
2. Hairy
3. Runt
4. Fushi - tarazu
5. Paired
6. Odd - paired
• Defect in any of these genes results in missing pattern
elements in alternate segment
• Defective even - skipped genes results in even number
parasegments missing in the body segments of the
Drosophila larva

16. 3) segment polarity genes
1. The pair rule genes activates the transcription of
segment polarity genes
2. Embryo will divide into well precise 14 segments with
correct location and definition
3. Main function of these genes is to decide the polarity
within each parasegment of the embryo
4. Engrailed and gooseberry are two common examples of
segment polarity genes

17. Homeotic selector genes
1. These are the master genes that regulates the
development of particular structure of body segment
2. Most homeotic genes codes a transcription factors
proteins that contains a region called homeodomain and
and are called hox genes
3. Mutations in hox genes can cause genetic disorders and
their overactivation and inactivation can develop the
body structures into different places than the original
location

18. Two clusters of homeotic gene control the most aspects of
segment polarity
Both complexes present on fruit fly chromosome -3
1. Antennapedia complex (ANT- C)
2. Bithorax complex(BX-C)
• ANT-C controls the segments in head and anterior thorax
• BX- C controls the segments in abdomen and posterior thorax

20. Homeobox
1. Many homeotic genes contain a
conserved DNA sequence
2. It is of 180 base pairs
3. It is known as homeobox
4. It is found in other eukaryotic
organisms too
5. These sequence encodes the 60
aa homeodomain
6. This recognise the specific DNA
sequence

21. Thank you