epistasis in case of alzheimer’s disease
understanding epistatic interactions may be the key to understand complex diseases, such as alzheimer’s disease, diabetes,
cardiovascular diseases and cancer. alzheimer’s disease, is a progressive neurodegenerative disorder that causes memory loss
and dementia. In the early 1990s, a number of scientists found that a gene called apolipoprotein E4 was associated with
a higher risk of developing alzheimer’s disease. However, the researchers also noted that while having one or two copies of
apolipoprotein e4 increases one’s risk of alzheimer’s, not all carriers of apolipoprotein e4 develop this disease. This suggested
that other genes and/or gene-gene interactions were involved in the development of alzheimer’s. eventually, it was confirmed
that 27 different significant epistatic interactions are involved which were grouped into five categories: cholesterol metabolism,
beta-amyloid production, inflammation, oxidative stress and other networks. Some interactions were synergistic, while others
were antagonistic. The synergistic interactions indicate that the pair of genes involved together increases the risk of alzheimer’s
disease. Meanwhile, the antagonistic relationships indicate a protective relationship between two genes.
Many of the other predictions of epistasis between genes could also prove to be significant if a larger population of alzheimer’s
patients were studied. Indeed, now that there is a foundation for understanding epistatic interactions between pairs of genes
in sporadic alzheimer’s disease, future studies can focus on epistatic interactions between combinations of three or more
genes and between additional pairs of genes.recessive epistasis
epistasis due to recessive gene is known as recessive epistasis, i.e., the recessive epistatic gene masks the activity of the dominant
gene at the other gene locus.
The dominant A expresses itself only when the epistatic locus C also has the dominant gene : if the epistatic locus has recessive gene
c, gene a fails to express.
Example: Onion bulb can have three types of pigmentation–red, yellow and white. When a pure red coloured onion is
crossed with a pure white coloured onion, the hybrids are all red coloured. In f 2 generation, three types of onion bulbs appear
- 9 red : 3 yellow : 4 white. The appearance of white colour is due to pigment inhibitor gene which is epistatic only in the recessive
state. In the dominant state, the gene allows the pigment producing gene (r) to express its effect. yellow colour is formed by the
residual genotype or recessive alleles (rr) of the pigment producing gene.
Selfing