1) The Orobanchaceae family (Order Lamiales) contains species that represent the
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1) The Orobanchaceae family (Order Lamiales) contains species that represent the full range of parasitic ability. Although a few species are completely non-parasitic (Mimulus spp.l), most members of the family are either hemi-or holoparasites Hooparss Figure 1. Comparison of features and evolutionary relationship among Orobanchacese species Inset: alternative evolutionary topology in which the terminal haustorium is suggested to have evolved independently in Striga and Orobanche.(Taken from Westwood et al 2010. Trends in Plant Science.15: 227-235) The 2N chromosome numbers vary somewhat among the species in Orobanchaceae, but the genome sizes vary greatly between the species. Briefly explain what genetic mutation(s) could account for such large increases in genome size but such small increases in chromosome number. Your explanation should clearly indicate that you understand how the mutotions might increase or decrease genome size. (5 pts)Explanation / Answer
In eukaryotic organisms, there is a paradox observed, namely that the number of genes that make up the genome does not correlate with genome size. In other words, the genome size is much larger than would be expected given the total number of protein coding genes . Genome size can increase by duplication, insertion, or polyploidization and the process of recombination can lead to both DNA loss or gain. It is also possible that genomes can shrink due to deletions.
An example of increasing genome size over time is seen in filamentous plant pathogens. These plant pathogen genomes have been growing larger over the years due to repeat-driven expansion. The repeat-rich regions contain genes coding for host interaction proteins. With the addition of more and more repeats to these regions the plants increase the possibility of developing new virulence factors through mutation and other forms of genetic recombination. In this way it is beneficial for these plant pathogens to have larger genomes.
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