1. Egg activation in fruit flies occurs after sperm-egg membrane fusion. True or
ID: 97962 • Letter: 1
Question
1. Egg activation in fruit flies occurs after sperm-egg membrane fusion. True or False?
2. Most homeotic genes are signaling molecules while pair-rule genes are transcription factors because cell membranes form a barrier for free diffusion of transcription factors. Therefore, gene expression can only be activated in cellular blastoderms by activation of signaling pathways. True or False?
3. Cytochalasin D, a microfilament disruptor, added to embryos just before gastrulation, would inhibit the gastrulation. True or False?
Explanation / Answer
1.
True.
In Drosophila, binding of sperm to the zona pellucida of the egg stimulates the acrosome reaction to take place which facilitates it to penetrate through the egg plasma membrane.
It is a cell-cell membrane fusion event which is essential for fertilization to produce a diploid zygote. Membrane fusion causes intracellular signaling events (Eg: Ca+2 signaling) inside the egg cell resulting in its activation.
2.
False
Homeotic genes are involved in regulating the development of segments/patterns of the body. Most homeotic genes code for transcription factors containing a particular domain called homeodomain.
Pair rule genes also encode transcription factors which regulate pair rule gene expression.
When syncytial blastoderm is converted into cellular blastoderm, transcriptional regulation is replaced by intercellular signaling. Cellular blastoderm can also show regulation of gene expression by diffusing factors.
3.
True.
Cytochalasin D belongs to a group of mycotoxins which bind to actin filaments and disrupt prevents polymerization. It is very effective in arresting the cell cycle.
Cytochalasin B inhibits morphogenetic movement required during gastrulation.
So, injection of Cytochalasin B into embryos inhibits gastrulation.
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