You do a screen for flower homeotic mutants in Arabidopsis and find many interes

Question

You do a screen for flower homeotic mutants in Arabidopsis and find many interesting candidates. Based on the phenotypes of the mutants, determine whether the mutation is an A, B, or C gene, or in multiple genes. A flower with sepals on the outside and carpels on the inside A flower with sepals on the inside and outside and petals in the middle. A flower with carpels on the inside and outside and stamens in the middle. A flower with all sepals. A flower with all carpels. In Drosophila, the genes that specify anterior posterior identity are sequentially expressed in which of the following orders maternal, pair rule, gap, homeotic, segment polarity maternal, segment polarity, gap, pair rule, homeotic homeotic, segment polarity, pair rule, maternal, gap maternal, gap, pair rule, segment polarity, homeotic gap, pair rule, segment polarity, maternal, homeotic

Explanation / Answer

7. b

8. B

Explanation:- Determination of cell fate is irreversible (determination) and is mediated by the segmentation genes. The segmentation genes are regulated by the maternal effect gen products and are transcribed zygotically. The segmentation genes fall into three classes based on their mutant phenotype.

Gap genes are some of the first genes to be expressed in the Drosophila embryo. They are both activated and repressed by the maternal effect genes and divide the embryo into broad regions that contain several segment primordia. Mutations in gap genes cause gaps in the segmentation pattern. Each of the gap genes encodes a DNA-binding protein that can activate or repress transcription.

The gap proteins interact with neighboring gap proteins to activate the transcription of pair-rule genes. The expression of the pair-rule genes divides the broad gap gene domains into para-segments. Mutations of the pair-rule genes usually delete portions of every alternative segment.

The Segment polarity genes are responsible for defining the segment boundaries. mRNA and protein products divide the embryo into 14 segment-wide units. The patterns of segment polarity gene expression reinforces the periodicitiy set up by earlier genes, establishes cell fates, and specifies segmental boundaries. Mutations in segment polarity genes cause a portion of each segment to be deleted and replaced by a mirror-image duplication of a another part of the segment. Segment polarity genes are expressed after cellularization and include transcription factors as well as components of cell-signaling pathways.

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