Question Set 2 Answer # 1 Ayok Monydit

1. What is the estimate of H2 for Cancer? How much influence does selection have on this?


H2 is defined as the proportion of total phenotypic variance at the populatioin level that is contributed by genetic variation. According Nature Reviews Cancer 4, 769-780 (October 2004) the h2 for this prevalent types of cancer are as follows.
Lung h2=0.26
Breast h2=0.27
Prostate=0.42
Colorectal=0.35

According to Carlo Maley, ans assistant professor at Wistar Univeristy, "the dynamics of evolution are fully in play within the environment of a tumor. A tumor cell population is constantly evolving through natural selection. Mutations that aid in the survival and reproduction of cells in a tumor are the things that drive it towards malignancy. When applying chemotrophy (cell chemistry) to a cluster of cancer cells, we are likely to find resistant mutant allele. 3 of Darwin's postulates are important when analyzing the evolution of cancer cells. These factors are genetic variation, heritabilty, and natural selection. Cancer cells are highly variable on a genetic level, no two cells will be completely identicle. Most Varation found in cancer cells is hertibale, that is, it is passed from parent to offspring. This excludes variation that is result of mutation. Last but not least, variation is acted upon by natural selection (some alleles possibly mutants become fixed or lossed). These 3 factors are the guidline for determining wheather a cancer cell will evolve or not.

References

http://www.sciencemuseum.org.uk/on-line/lifecycle/79.asp

http://www.hhmi.org/biointeractive/cancer/cancer_evolution.html

Genetic predisposition to colorectal cancer
Nature Reviews Cancer 4, 769-780 (October 2004)
doi:10.1038/nrc1453