Evolution and Genetic Engineering - Bioprocess Engineering: Kinetics, Biosystems, Sustainability and Reactor Design - page 702

Aneuploidy involving the sex chromosomes is common. XYY males are normal but XXY
males and XXXY males have a syndrome called Klinefelter syndrome. These males are often
actually intersexed or hermaphroditic with partially developed sexual organs of both
genders. These individuals are sterile and are often subjected to hormones and surgery to
bring them into conformance with social gender roles.
Polyploidy refers to a genome consisting of more sets of chromosomes than usual in
a nucleus. Polyploidy can happen because of a failure of the spindle fibers in mitosis or
meiosis to segregate chromosomes into separate groups. Many organisms have specialized
polyploid tissues, even organisms we typically consider as diploid. For example, in plants,
a so called double fertilization leads to the genesis of a diploid zygote from the union of
two gametes produced by the haploid gametophytes but also a specialized triploid tissue
(3N) called endosperm. This tissue is produced when a male gamete fertilizes special diploid
tissue from the flower.
In mammals, cells of the liver are typically polyploid. Some organisms are completely
polyploid including many plant species and some fish and amphibians. For example,
domestic wheat is hexaploid (6N). “Seedless” plants are usually triploid (3N). Polyploidy
is believed to be an important mechanism in the development of new species and a common
pattern in plants is to find populations of two species both of which might be diploid.
14.2. SELECTION
14.2.1. Natural Selection
Natural selection is the process that results in an increase in the number of those individ-
uals of a population that have a variation (or mutation) in a particular trait (or traits) that
provide the bearers with an advantage for survivability and reproducibility. These variants
or mutants and their offspring survive and reproduce more succesfully, and will increase
in number overtime.
Natural selection works with the phenotypic or observable characteristics of an organism.
The genetic basis of the phenotypic change becomes more prevalent in the population over-
time, resulting in the adaptations that specialize organisms for particular ecological niches
and eventually may result in the emergence of a new species.
Conversely, if a genetic variation or mutation has resulted in a phenotypic change that
makes a particular individual less survivable or less fit for the environment, due to this
natural selection process, the chances of survival and reproduction for that individual are
reduced, resulting in the elimination of the genetic change overtime.
An adaptation method of E. coli to wood extract hydrolyzates has been described by Liu
et al. (T. Liu, L. Lin, Z. Sun, R. Hu, S. Liu. 2010 “Bioethanol fermentation by robust
recombinant E. coli FBHW using hot-water wood extract hydrolyzate as substrate”
J. Biotech. Adv., 28: 602 e 608.) as shown in Fig. 14.1 . Wood extract hydrolyzate is a complex
mixture of sugars (xylose, glucose, mannose, arabinose, etc), phenolic derivatives (from
lignin), and electrolytes. Initially, E. coli fbr5 does not grow in the wood extract hydrolyzate
or to produce ethanol. After the natural adaption, E. coli fbr5 mutant strains become
productive.