D.melanogaster

8/7/2019 D.melanogaster

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Drosophila melanogaster


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Classification

Domain : EukaryaKingdom : AnimaliaPhylum : Arthropoda

Class : InsectaOrder : DipteraSuborder : BrachyceraFamily : DrosophilidaeSubfamily: DrosophilinaeGenus : Drosophila ("dew lover")Species : melanogaster ("dark gut")


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Drosophilamelanogaster

Bilaterally symmetric segmented body

Head

Thorax

Abdomen


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Introduction

Dipteran insect.

Sexually dimorphic and both sexes display various

morphological differences in primary and secondary

sexual characters. Morganwas the first to discover sex-linkage and

genetic recombination, which placed the small fly in the

forefront of genetic research.

Flies have a short generation time (10-12 days) and do

well at room temperature.


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Contd

Exhibits complete metamorphosis.

Females are about 2.5 millimeters (0.1 inches) long.

Males are slightly smaller and the back of theirbodies is darker.

The compound eye of the fruit fly contains 800 unit

eyes orommatidia(8 photoreceptor cells , supportcells, pigment cells, and a cornea).

It has only four pairs of chromosomes: three

autosomes, and one sex chromosome.


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Drosophila natural history

Originated in Africa.

Probably spread by human

activity. Likes compost, rotting

fruit, yeast.

Harmless (mostly).

Strains collected

subsequently have P

transposable elements and

cant easily be used.


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Life Cycle

The Drosophila life cycleconsists of a number ofstages:

Embryogenesis

Three larval stages

A pupal stage, and

An adult stage.

The lifespan is about 30 daysat 29 C (84 F).

Females can lay up to 100eggs/day.


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Life cycle ofDrosophila

4 stages: embryo, larva, pupa, adult

Culture condition: 250C and 60% humidity


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Contd

The mean durations of development in the pupae

were measured at combinations of 6 constant

temperatures (15, 20, 22.5, 25, 27.5 and 30C) And up to 11 levels of relative humidity.

The thermal survival range for the pupae is between

15 and 30C, and the humidity viable range is

between 60 and 100% RH.


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Early development of Drosophila

Rapid division

8 mins/division

9 divisions13 divisions

Single cell

asynchronous


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Life cycle by Day

Day 0 : Female lays eggsDay 1 : Eggs hatchDay 2 : First instar (one day in

length)Day 3 : Second instar (one day inlength)

Day 5 : Third and final instar (twodays in length)

Day 7 : Larvae begin roaming stage.Pupariation (pupal formation)occurs 120 hours after egg laying

Day 11-12: Eclosion(adults emergefrom the pupa case)


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Different stages of development


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Embryogenesis in Drosophila

Mitosis begins following fertilization First ten divisions include no growth and Cytokinesis

Single multinucleate cell results - syncytium, orsyncytial blastoderm.

At the tenth nuclear division,the nuclei migrate to the peripheryof the embryo.

At the thirteenth division, so nucleiare partitioned into separate cells.This stage is the cellular blastoderm.


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Geneactivation

The genes that code for mRNAs are called maternaleffect genes (bicoid and nanos) are required during

oogenesis

One group of maternal effect genes establishes the

anterior-posterior axis of the embryo Another set of maternal effect genes establishes the

dorsal-ventral axis

Regulates the expression of the gap genes. Female flies possessing mutations in maternal effect

genes appear phenotypically normal, but produce

offspring with mutant phenotypes


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Maternal effect genes

Maternal genes by group

Anterior group

Bicoid egg-polarity gene

Bicoid interacting protein 1

ExuperantiaStaufen etc.

Posterior group

Oskar(assembly of germplasm)Terminal group

capicua

corkscrew


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Bicoidgene

Concentrated at anterior end of fly embryo

Gradient of gene product

Essential for setting up

anterior end of fly

Gradients of other proteinsdetermine the posterior end

and the dorsal-ventral axis

The bicoid genes are

transcription factors

Regulate the expression of

some of the embryos genes


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Conversion ofMaternal Protein Gradients intoZygotic Gap GeneExpression

Transcription factor


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Gastrulation

The mesodermal tube forms from ventral tissue then cellsseparate & move to internal locations under theectoderm.

The mesoderm becomes muscle and connections tissues.

In insects, the nerve cord lies ventrally . Neuroblasts form a layer between mesoderm and outer

ectoderm.

The midgut (anterior & posterior) grow from threads and

fuse. Ectoderm becomes epidermis.

No cell division occurs during gastrulation but divisionrestarts afterward.


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Contd

Seven other events resembling Gastrulation are listedbelow:

1) formation of the cephalic furrow 2) formation of dorsal transverse folds

3) germ band extention

4) germ band retraction 5) segmentation

6) dorsal closure

7) head involution


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The sequential expression of different sets of genes establishes the body plan along the anterior-posterior axis

Localized mRNA and

ProteinsT

ranslated afterfertilization

Positional information to

activate zygotic genes

parasegment

Pattern in the segment

Segment identities

Temporal sequence

The sequential expression of different sets of genes establishes the body planalong the anterior-posterior axis


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Segmentation

The germband (ventral blastoderm) is the main trunkregion.

The process of germ band extension pushes the posterior

end over dorsal side. The first signs of segmentation grooves appear to outline

parasegments which give rise to segments.

Segments are formed from the posterior of one

parasegment and the anterior of the next. There are 14 parasegments: 3 mouth, 3 thorax, and

8 abdominal.


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Segmentation


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Segmentation genes Three sets of segmentation genes are activated

sequentially Gap genes

Pair-rule genes

Segment polarity genes

The activation of these sets of genes defines the

animals body plan

Each sequential set regulates Genes of embryo

Expression regulated by products of egg-polarity genes

Direct the actual formation of segments after the embryos

major axes are defined

Involved in the segment patterning.


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Gap genes

The gap genes roughly subdivide the embryo along the

anterior/posterior axis

Map out basic subdivisions along the embryos anterior-

posterior axis

Mutations cause gaps in the animals segmentation


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Pair-rule genes

Define pattern in terms of pairs of segments

The pair-rule genes divide the embryo into pairs of segments.

Mutations result in embryos having half the normal number

of segments


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Gap genes Pair-rule genes

Buttonhead

hunchback

caudal collier

empty spiracles

Krppel

orthodenticle

knirps

even-skipped

fushi tarazu

odd-paired odd skipped

paired

runt

sloppy paired Tenascin

major


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Segment polarity genes

Set the anterior-posterior axisof each segment

Mutations produce segments

where part of the segment

mirrors another part of the

same segment


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Summary

Products of the egg-polarity genes regulate theregional expression of the gap genes

Gap genes control the localized expression of the pair-rule genes

Pair rule genes activate specific segment polarity genesin different parts of each segment

Segment polarity genes activate homeotic genes


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HOMEOTICGENES

Master regulatory genes Encode transcription factors

Control the expression of genes responsible for specific

anatomical structures Mutations produce flies with structures in incorrect places


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HOMEOTICGENES

Homeotic genes of Drosophila all possess homologous

segments

180-nucleotide sequence = homeobox

Encodes 60-amino-acid homeodomain

Homologous sequences have been found in many

other animals

e.g., Insects, nematodes, mollusks, fish, frogs, birds,humans, etc.

Related genes are even found in yeast, etc.

Hox genes


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Larvae The larvae hatch at 24 hrs

post-fertilization.

1. The anterior end is the acron.

2. The posterior end is the telson.

Along with the head, thelarvae has 3 thoracic segments

and 8 abdominal segments.

The ventral side of the larvae

has denticle belts, alternating

patches of denticle hairs and

cuticle on each segment, used

for locomotion.


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Developmentalstages

Larva eventually forms a pupa Enclosed in a case

Metamorphosis occurs

Change from larva to adult fly Adult fly emerges from case

Each segment is anatomically distinct


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Metamorphosis

Three instar stages of larval life are separated by molts.1st instar --> 2nd instar --> 3rd instar

Third instar larvae forms pupae (pupation) to undergometamorphosis.

The adult tissues arise from imaginal discs andhistoblasts.

The imaginal discs are small sheets of epidermis (~40 cellseach of cellular blastoderm) which grow throughout

larval life.

6 leg, 2 wing, 2 haltere, 2 eye-antenna, plus genital, headdiscs and ~10 histoblasts.


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FlyBase

FlyBase provides an integrated view of the fundamentalgenomic and genetic data on the major genetic model

D.melanogaster and related species.

FlyBase has primary responsibility for the continual

reannotation of the D. melanogaster genome. The ultimate goal of the reannotation effort is to

decorate the euchromatic sequence of the genome with as

much biological information as is available from the

community and from the major genome project centers.

FlyBase entries include maps, gene products and

ontologies, structured phenotypic and gene expression

data, and anatomy.


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Thank you

D.melanogaster

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