Ch. 21 I'm Exhusted. Flashcards
EpiGENESIS
How embryo develops
Epigenetics is alterations to _______ that affect ____ and are ________ but are NOT _______________________________.
Epigenetics is alterations to DNA and Chromatin structure that affect traits and are passed on to other cells or generations but are NOT caused by changes in DNA base sequences.
Changes in chromatin structure alter
gene expression
Name 3 molecular mechanisms that alter chromatin structure
- Changes in patterns of DNA methylation
- Chemical modification of histone proteins
- RNA molecules that affect chromatin structure and gene expression
DNA methylation
Repression of transcription
CpG dinucleotides
Prevents transcription factors from binding
Located near or in promoters
Attracts histone deacetylases or methyl transferases
How is methylation maintained
Template strand methyl groups attract methyltransferases, which add methyl groups to unmethylated strands
This is how epigenetic changes are retained and replicated through the process of chromosome replication
How are Queen Bees created?
Royal Jelly: Inhibiting Dnmt3, causing demethylation
Histone Modifications
Phosphates, methyl (effect varies), acetyl (more transcription when added), ubiquitin
Histone modifications which don’t involved base sequence that are associated with level of transcription are called
Epigenetic markers
Histone modifications are added and removed by _____, a group of proteins that (repress/active) transcription by modifying histones.
polycomb group (PcG)
Repress transcription
One histone may affect whether addition marks occur nearby and how they function. This is called
Crosstalk
Paramutation
interaction between two alleles that leads to heritable change in expression of one allele
2 important features of paramutation
- newly established expression pattern of converted allele is transmitted to future generation, even though allele is no longer present
- Altered allele now able to convert other alleles to the new phenotype
Paramutation in Mice: Why do some kit(t) kit(t) mice have white feet and tails
miRNAs that degrade the Kit in mRNA, transmitted through gametes
Paramutation in Corn: How does B’ convert B-I allele to B’*
siRNAs encoded by tandem repeats
Modify chromatin structure by directing DNA methylation
Describe X inactivation
Xist gene transcribed to lncRNA, which coats Xi but not Xa. The Xist RNA recruits PCR2 which produces histone modifications on Xi.
What inhibits transcription of Xist on ACTIVE chromosome?
Tsix
What stimulates transcription of Xist on INACTIVE chromosome?
Jpx
What sustains Tsix expression on active X, which inhibits Xist and maintains transcription of genes on active X chromosome.
Xite
What is it called when sex of parent that contributed the allele influences how allele is expressed, and why does this happen?
Genomic Imprinting
Due to different degrees of methylation of the alleles inherited from the two parents
Genomic Imprinting: Mice example
When mutant from father, expressed, but not if from mother
The overall pattern of chromatin modifications possessed by each individual organism
Epigenome
How are histone modifications detected?
ChIP- break chromatin into fragments, applies antibody specific to particular histone modification. (Rest explained in pervious chapters)
Detecting DNA methylation: 2 methods
- Restriction endonucleases
2. Bisulfate sequencing
