Christiane Nüsslein-Volhard and her colleagues carried out several experiments in an attempt to understand what determines the a
nterior and posterior ends of a Drosophila larva (reviewed in C. NüssleinVolhard, H. G. Frohnhofer, and R. Lehmann. 1987. Science 238:1675– 1681). They isolated fruit flies with mutations in the bicoid gene (bcd−). These flies produced embryos that lacked a head and thorax. When they transplanted cytoplasm from the anterior end of an egg from a wild-type female into the anterior end of an egg from a mutant bicoid female, normal head and thorax development took place in the embryo. However, transplanting cytoplasm from the posterior end of an egg from a wild-type female into the anterior end of an egg from a bicoid female had no effect. Explain these results in regard to what you know about proteins that control the determination of the anterior–posterior axis.
Bicoid gene is the maternal effect gene whose protein concentration gradient patters the anterior-posterior axis in Drosophila embryogenesis. It was the primary protein that is demonstrated to act as a morphogen. Morphogens are proteins whose concentration gradient will affect the developmental fate of the surrounding region.
The specified bicoid gene is the one which codes for bicoid protein. This protein is being existing in a gradient manner in the egg and thus its concentration is higher at the anterior end and lower in posterior end.
This bicoid protein is responsible for the stimulation of the development of the anterior end.
The posterior region (including the hindgut) expands and extends towards the anterior pole along the dorsal side of the embryo. At this time, segments of the embryo become visible, creating a striped arrangement along the anterior-posterior axis.
New species can appear gradually through small changes in an ancestral species.
Explanation:
The new species that appear are due to hereditary variations that occur in a population. The adaptive variations are said to confer a selective advantage to organisms possessing them. The result of variations is that well adapted individuals are able to survive and reach the reproductive age and pass over their favourable characteristics to their offspring.
<span>A solution is the mixture of two or more substances. One of them is called the solute and the other is the solvent. A solute is the substance to be dissolved (sugar). The solvent is the one doing the dissolving (water). Therefore, suder is the solute and water is the solvent. Option C is the correct answer.</span>