The Role of Maternal Genes in Embryonic Development
The link between genes and human behavior has been a subject of scientific research since before the discovery of DNA in 1953. There is still much that is unknown about how human genes interact with biological and chemical processes and the extent to which those processes are affected by the environment. Epigenetics is the study of how the expression of genes is modified by factors such as social experiences, diet and nutrition and exposure to toxins. Behavioral epigenetics examines the role of epigenetics in shaping behavior.
Children share half of their alleles with each parent. The maternal genes contribute the maternal gamete which develops as an egg that becomes an embryo when fertilized. Maternal genes containing RNA and protein are present before the development of zygotic genes that takes place after fertilization. The development of the embryo relies exclusively on maternal genes for its early development processes until the embryonic genome is activated. In humans, the embryonic genome is activated within 4 cleavage cycles.
How Maternal and Paternal Genes Affect Parenting Style
Parenting styles can be affected by both maternal and paternal genes in combination with the environment. Michael Meaney provided the first documented example of epigenetics affecting behavior in 2004, when his research team found that how a rat responds to stress later in life is affected by the amount of nurturing a mother rat provides during infancy. Nurturing behaviors stimulate activation of pathways that remove methyl groups from DNA, allowing the glucocorticoid gene, which lowers stress response, to be activated.
Epigenetics provides evidence that the nature versus nurture controversy has been resolved and that each is shaped by the other through a series of complex chemical, biological and environmental interactions. One article about how parenting styles are affected by behavioral epigenetics points out that environmental stress can cause methyl groups to become attached to genes. This causes epigenetic changes that can be passed down from generation to generation through affected maternal genes.
How Environment Can Affect Paternal and Maternal Genes
One study compared brain samples of 36 victims of suicide. The one third of those who were known to have suffered childhood abuse showed distinct epigenetic methylation marks or characteristics in their DNA that were not present in the control group or the group with no known childhood abuse. Those marks specifically influenced the hypothalamic-pituitary-adrenal function of the brain. Another study revealed that poverty can also change the way in which DNA is expressed. Blood samples of 40 men all born in 1958 from differing economic backgrounds revealed genetic changes based on family income during childhood.
However, not only economic poverty, but a poverty of physical affection can also affect gene expression. Researchers compared blood samples of 14 children being raised in Russian orphanages with blood samples of 14 children being raised by their biological parents. The children in the orphanage were found to have a greater degree of methylation in the genes affecting neural communication and brain development than the children receiving more individual attention from parents.
These discoveries about how maternal and paternal genes are affected by environmental factors have raised the question of whether some mothers parenting skills may be adversely affected by their DNA. According to a recent paper, RS3, an allele of one of the potential maternal genes, the AVPR1A gene, was linked in a study to lower levels of maternal behavior in women and in more aggressive behaviors in children. Not everyone carries this allele, but it is fairly common in humans and has also been associated with some forms of autism.
The most exciting aspect of these scientific discoveries about the interaction genes with the environment is that one day all prospective parents will have the necessary information to help them make healthy parenting choices. They provide scientific evidence of what most parents already knew—that parenting choices have the power to affect generations to come. Hopefully, this knowledge will be used to create social programs that will educate parents and provide whatever degree of assistance necessary to enable them to use that power wisely.