27 Statement I. Maternal effect genes are a class of Drosophila genes regulated

Question

27 Statement I. Maternal effect genes are a class of Drosophila genes regulated by the protein products of the gap, pair-rule, and segment polarity genes whose transcription determines the developmental fate of each segment. Statement 2. Pair-rule genes are Drosophila zygotic genes regulated by proteins which divide the embryo into periodic units, resulting in a striped patterm of seven transverse bands perpendicular to the anterior-posterior axis. Pair-rule mutants lacked portions of every other segments. a. Both statements are true. b. Both statements are false. c. Statement 1 is false and statement 2 is true. d. Statement 2 is false and statement 1 is true.

Explanation / Answer

Ans:- C statement 1 is false & statement 2 is true.statement 1 is false because matrnal effect genes in drosophila are pr in egg prior to fertilization so they are expressed even before fertilization. They maintain polarity of egg. These genes if expressed properly then only further expression of Gap genes, pair rule genes, segment polarity genes and proper development of embryo will takes place.

Due to expression of Gap genes, pair rule genes, segment polarity genes- Homeotic genes.are expressed.

Statement 2 is true.when gap genes expressed they divide embryo in 3 regions HEAD, THORAX, ABDOMEN. After expression of Gap genes pair rule genes are expressed which further divide embryo in 7 parasegments( striped pattern of 7 transverse bands). When pair rule genes are mutated every alternate segment is affected.pair rule genes consist of early pair rule genes and late pair rule genes. Early pair rule include expression of HAIRY, EVEN SKIPED, RUNT genes. Out of these when Even skipped is mutated every even segment will be defective. Late pair rule genes include expression of FUSCHI TARAZU, ODD SKIPPED, ODD PAIRED, PAIRED, SLOPPY PAIRED. When any of the genes is mutated every odd segment will be defective.

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