Essay- Answer 2 of the 3 essay questions in the space provided. Please write com

Question

Essay- Answer 2 of the 3 essay questions in the space provided. Please write complete sentences in the space provided and draw any figures that you feel necessary. (12pts each) 1) Describe in detail how Charles Lyell, Carolus Linnaeus, Thomas Malthus, Lamarck's contributions to science influenced Darwin's thinking about the origin of species describe the formation of a hybrid zone and the possible outcomes for the hybrids over- ie 3) Describe Thomas Hunt Morgan's experiment with fruit flies where he discovered chromosomal inheritance

Explanation / Answer

2. Hybrid zones are areas where the hybrid offspring of two divergent taxa (species, subspecies or genetic "forms") are prevalent and there is a cline in the genetic composition of populations from one taxon to the other.

A hybrid zone exists where the ranges of two interbreeding species or diverged intraspecific lineages meet and cross-fertilize. Hybrid zones can form in situ due to the evolution of a new lineage but generally they result from secondary contact of the parental forms after a period of geographic isolation, which allowed their differentiation (or speciation). Hybrid zones are useful in the study of the genetics of speciation as they can provide natural examples of differentiation and (sometimes) gene flow between populations that are at some point between representing a single species and representing multiple species in reproductive isolation.

When closely related species meet in a hybrid zone, there are three possible outcomes:

3. One day in 1910, American geneticist Thomas Hunt Morgan peered through a hand lens at a male fruit fly, and he noticed it didn't look right. Instead of having the normally brilliant red eyes of wild-type Drosophila melanogaster, this fly had white eyes. Morgan was particularly interested in how traits were inherited and distributed in developing organisms, and he wondered what caused this fly's eyes to deviate from the norm. Morgan's fly lab at Columbia University was already in the habit of breeding Drosophila so that the researchers there could observe the transmission of genetic traits through successive generations, so Morgan chose to do a simple breeding analysis to find out more about white eyes. Little did Morgan know that, with this white-eyed fly, he was about to confirm the chromosome theory. In doing so, Morgan would also be the first person to definitively link the inheritance of a specific trait with a particular chromosome.

he first performed a test cross between the white-eyed male fly and several purebred, red-eyed females to see whether white eyes might also occur in the next generation. The members of the resulting F1generation had all red eyes, but Morgan suspected that the white-eye traitwas still present yet unexpressed in this hybrid generation, like a recessivetrait would be. To test this idea, Morgan then crossed males and females from the F1 generation to probe for a pattern of white eye reoccurrence. Upon doing so, he observed a 3:1 ratio of red eyes to white eyes in the F2generation. This result is very similar to those reported for breeding experiments for recessive traits, as first shown by Mendel. Strangely, however, all of Morgan's white-eyed F2 flies were male, just like their grandfather—there were no white-eyed females at all! Correlation of a nonsexual trait with male or female identity had never been observed before. Why, Morgan puzzled, would this particular trait be limited to only males?

Later on he continued his experiments and concluded that sex linked inheritance was taking place in fruit flies.

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