BIOM 503
LIBERTY UNIVERSITY
FALL 2020
BIOM 503
HUMAN GENETICS
LECTURE ASSIGNMENT 8 INSTRUCTIONS
Compose a paragraph-style response for the essay topics listed below. The assignment MUST
reflect your own understanding of the course material.
1. High levels of homocysteine can cause negative effects on cells. Give 2 examples (1
transcriptional and 1 non-transcriptional) that might explain this mechanism.
2. Why is folate-supplementation late in life possibly harmful to those who have had a
folate-deficient diet most of their life?
3. What is the conflict theory and how is the Igf2/H19 locus an example of this theory?
3. Genomic imprinting is where paternal and maternal alleles are expressed differently
in mammals. The patterns of genomic imprinting had several explanations however, the
most successful explanation was a theory named The Conflict Theory.
The conflict hypothesis suggests that the genes expressed on the paternal alleles
should stimulate growth while the genes expressed on the maternal alleles should
prevent it. The balance of the genome is caused by the balance between growing and
not growing.
According to the article “Genomic imprinting in mammalian development: a parental tug-
of-war” by Moore and Haig, the genomic imprinting is described as a “tug of war”
between maternal and paternal alleles.1 The conflict theory suggests that the males
care only about their children and try to find the best strategy to get the maximum
amount of resources for them at the expense of the mothers and her future children by
other males. Whereas mothers try their best to find and divide resources equally
between her offspring by using imprinting or DNA methylation.
One compelling example of this theory is the IGF2 and IGF2R genes. IGF2 gene is a
gene that promotes growth and is is expressed on the paternal genome. When IGF2
gene is mutated, the growth rate is reduced by 40%. On the other hand, IGF2R gene is
expressed on the maternal genome and its function is to keep the embryo size smaller.
When IGF2R is mutated, the embryo becomes oversized. However, when both IGF2
and IGF2R genes are mutated, the embryo grows up normally.
The Conflict Theory has some detractors. One of the detractor is that it is too flexible
and can be used to explain anything.
BIOM 503
References:
1. Moore, Tom, and David Haig. “Genomic Imprinting in Mammalian Development:
a Parental Tug-of-War.” Trends in Genetics, vol. 7, no. 1, 1991, pp. 45–49.,
doi:10.1016/0168-9525(91)90040-w.
