BIOM 503
LIBERTY UNIVERSITY
FALL 2020
BIOM 503
HUMAN GENETICS
LECTURE ASSIGNMENT 5 INSTRUCTIONS
Compose a paragraph-style response for the essay topics listed below. The assignment must
reflect your own understanding of the course material.
1. Describe the theory of heterochromatinization and what this theory predicts about global
gene expression with time.
2. Based on the introduction of “Formation of Boundaries of Transcriptionally Silent
Chromatin by Nucleosome-Excluding Structions,” give 3 models that might explain how
boundary or insulator elements protect a gene from the influence of nearby genomic
regions.
3. Briefly describe the 3 assays the authors used in the aforementioned paper to demonstrate
that LexA did not have gene activating activity.
4. Briefly explain how each of the following is an example of position-effect variegation:
a) Burkitt’s lymphoma,
b) Alpha-thalassemia, and
c) Progeria.
1. Heterochromatinization is the process of converting euchromatin into heterochromatin
during the inactivation of the X chromosomes in early stage in embryogenesis of
mammalian females. Hetrerochromatin is the tightly packed form of DNA and is often
inactive and euchromatin is the lightly packed form of chromatin and is often active.
The theory of heterochromatization describes how heterochromatin will spread with age.
Telomere shortening occurs as we age and it happens because of errors in replication
where there is some inefficiency with replicating the ends of DNA. Telomoere shortening
causes heterochromatin spreading. When telomere shortening happens, the repressive
proteins, chromotosomes and histone deacetylases can be redistributed to non-
telomeric sites. The X-inactivate specific transcript (Xist) RNA covers the X chromosome
and recruits silencing proteins.
BIOM 503
The theory predicts that global genes with higher expression might express themselves
in the future due to X-linked gene reactivation (Yu et al., 2019). The X chromosomes
DNA methylation status influences the gene expression domination. The silenced X
chromosome may replicate early in the S-phase, resulting in gene transcription.
References:
1. Yu, S., Chen, C., Pan, Y., Kurz, M. C., Datner, E., Hendry, P. L., ... & McLean, S. A.
(2019). Genes known to escape X chromosome inactivation predict co‐morbid chronic
musculoskeletal pain and posttraumatic stress symptom development in women
following trauma exposure. American Journal of Medical Genetics Part B:
Neuropsychiatric Genetics, 180(6), 415-427.
