What are the important characteristics of an epigenetic trait?
An epigenetic trait is one that is stable and passed on to cells or offspring but does not involve changes to the DNA base sequence. Many epigenetic traits are caused by changes in gene expression resulting from modifications to chromatin. Although stable
What three molecular mechanisms alter chromatin structure and are responsible for many epigenetic phenotypes?
(1) changes in DNA methylation; (2) chemical modifications of histone proteins; and (3) RNA molecules that affect chromatin structure and gene expression.
What is the major form of DNA methylation that is seen in eukaryotes? At what type of DNA sequence is DNA methylation usually found?
The major form of DNA methylation seen in eukaryotes is 5-methylcytosine. In eukaryotes, DNA methylation is often seen at CpG dinucleotides. Additionally, in plants, DNA methylation is also frequently seen at CpNpG trinucleotides.
How does DNA methylation repress transcription?
The methyl group of 5-methylcytosine sits within the major groove of the DNA and may inhibit the binding of transcription factors and other proteins required for transcription to occur; 5-methylcytosone attracts proteins that directly repress transcriptio
Briefly explain how patterns of DNA methylation are transmitted across cell division.
Methyltransferase enzymes recognize the hemimethylated state of CpG dinucleotides following replication and add methyl groups to the unmethylated cytosines, resulting in two new DNA molecules that are fully methylated.
What types of histone modifications are responsible for epigenetic phenotypes?
Modifications of histone proteins especially in the positively charged tail are responsible for many epigenetic changes. The histone modifications include covalent modifications such as the addition or removal of chemical groups such as acetyl groups, met
How is X inactivation an epigenetic phenotype?
X inactivation in female mammals occurs when one X chromosome in each cell is randomly inactivated turning off much of the gene expression of the inactivated chromosome. The change in gene expression due to the inactivated X chromosome in one cell can be
Briefly describe the molecular processes that cause one X chromosome in each female cell to be active and the other X chromosome to become inactivated.
The X-inactivation center, a 100,000 to 500,000 bp region within the X chromosome, contains genes that can initiate X chromosome inactivation and other genes that maintain X chromosome activation. Within the X-inactivation center, the Xist gene codes for
Define genomic imprinting.
In genomic imprinting, the sex of the parent that contributed the allele to the offspring determines if the expression of the transmitted allele occurs within the offspring.
What is the epigenome?
The epigenome refers to the overall nature and types of chromatin modifications possessed by an organism.
How do epigenetic traits differ from traditional genetic traits, such as the differences in color and shape of peas that Mendel studied?
The phenotypic differences in traditional genetic traits such as the color and shape of peas that Mendel studied are due to differences in the DNA base sequences within the alleles. In epigenetics, the phenotypic differences are not due to changes in alle
What would be required to prove that a phenotype is caused by an epigenetic change?
Epigenetic effects are traits that are heritable in the sense that they are passed on to other cells or across generations. So, a first step would be to show that the phenotype was stable across cell divisions or generations. To rule out direct environmen