Lecture 31 - Developmental genetics I Flashcards Preview

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Time for drosophila fertilized egg to adult fly

10 days


3 stages of drosophila development and time for each

Embryonic stage (1 day), larval stage (4-5 days), Pupal stage (4-5 days)


Embryonic stage description

1 cell becomes alive animal with muscle, nervous system, trachea, ...


Larval stage description

Growth stage, eats a lot and increases size and weight


Pupal stage description

Metamorphosis (transition from growth stage to reproductive stage). Reorganisation of tissues. Controlled by hormones


3 main features of embryonic stage

No zygotic transcription until 2h into embryogenesis
No plasma membrane (syncytium) in early embryogenesis
Maternal factors regulate early embryogenesis


4 steps of the 2 first hours of embryogenesis (and time)

Single-celled diploid zygote
Multinucleated syncytium (70 min)
Syncytial blastoderm (120 min - 2h)
Cellular blastoderm (180 min - 3h)


Multinucleated syncytium description

9 nuclear divisons but still 1 cell in 1 membrane -> multinucleated syncytium


Syncytial blastoderm description

Nuclei migrate to the periphery of the embryo and divide 4 more times. Pole nuclei on one end


Cellular blastoderm description

Cell membrane grows around each nucleus. Pole nuclei become pole cells (primordial germ cells) on one end


Description of the 2 hour embryo (syncytial blastoderm)

4 segments (anterior/posterior + dorsal/ventral) established


Description of the 10 hour embryo

Number and orientation of segments (within segments) established. Distinguish head, thoracic segments and abdominal segments


Observing drosophila embryogenesis video : 3 things to note

13 synchronous divisions - 8000 nuclei. Back and forth pulling and stretching coordinated movement. Separation of segments and orientation


Heidelberg screen what + goal

Mutagenesis screen (forward genetics) to ID genes required for organizing the drosophila embryo


2 screens in the Heidelberg screen

1. For genes required in the mother for normal development of the embryo
2. For genes required in the embryo's genome


Name of genes in the first screen done and idea behind it (why do it)

Maternal-effect genes. Early embryo: maternal mRNA deposited into the egg and required for early dev. before zygotic transcription


What determines if embryos of a mother will have normal or mutant phenotype associated with early dev. (before zygotic transcription)

Mother has to carry one copy of maternal-effect gene and all offspring will be normal


Maternal-effect gene, offspring phenotypes in these crosses. m/+ father x m/+ mother. m/m father x m/+ mother. anything father x m/m mother.

Normal. Normal. Mutant.


Maternal effect gene : m/+ father x m/+ mother -> 1 +/+ , 2 m/+ , 1 m/m -> phenotypes of these offsprings

All normal, even the m/m offspring (simply because mother is m/+ and carries a WT copy of the maternal-effect gene)


Name of genes in second screen and inheritance pattern followed

Zygotic genes. Mendelian inheritance pattern.


m/+ father x m/+ mother for zygotic genes. offspring pheno ratio

3 normal (+/.) 1 mutant (m/m)


Common characteristic the identified genes were found to have

Most are transcription factors


5 categories they put the genes from the screen in + maternal-effect or zygotic. + based on what

Based on ressemblant mutant phenotype. Egg-polarity genes (maternal). Gap genes, pair-rule genes, segment polarity genes, segment identity genes (zygotic)


Maternal effect genes general function

Establish anterior-posterior (AP) axis


2 maternal-effect genes + function and type

Bicoid (TF) : anterior structures (head, thoracic segments)
Nanos (translational repressor protein): posterior segments (abdominal)


Regions affected in bicoid and nanos mutant

Bicoid mutant: Anterior embryo affected
Nanos mutant: Posterior embryo missing/affected


Observation when labelled bicoid protein in white

Localizes more to anterior region and less and less to posterior region


General conclusion about the observation on bicoid gradient

Factors (mRNA) from the mother localize to specific regions. Embryo's nuclei are all exposed to different amount of each protein.


Bicoid mRNA localization and where it is translated

Localized in anterior region only. Translated in anterior region into bicoid protein


Bicoid protein localization and how is this important

Diffuses because still multinucleated syncyntium. Gradient from A to P. More in A and less and less towards P. *Gives information on distance from anterior*