Lecture 31 - Developmental genetics I Flashcards
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
- For genes required in the mother for normal development of the embryo
- 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)