Lecture 21 Chapter 21 Flashcards
epigenesis
how an embryo develops
genetics
the study of genes and heredity
epigenetics
○ Heritable modification that does not involve changes in DNA
thrifty hypothesis
assumes that when environmental conditions are poor for the parent, they are likely to also be poor for the offspring. Therefore, when the parent experiences food shortage, biochemical modifcations allow pre-adaptations to produce offspring that are metabolically thrifty, eating as much as possible, minimizing energy expenditure, and hoarding/conserving calories
DNA methylation
addition of methyl groups to nucleotide bases
most common: methylation of cytosine to produce 5-methylcytosine
generally methylated cytosines are associated with gene repression
stably maintained through DNA replication
Acetylated histones
generally acetylated histones are associated with gene activity
What are some types of histone modifications?
- more than 100 different posttranslational modifications of histone proteins
modifications include addition of:
- phosphates
- methyl groups
- Acetyl groups
- ubiquitin
What are some epigenetic effects by RNA molecules?
examples
- X inactivation by Xist
- Paramutation in corn by siRNAs
Paramutation
an interaction between two alleles that leads to a heritable change in expression of one of the alleles
Behavioral epigenetics
life experiences, especially early in life, have long-lasting effects on behavior
genomic imprinting
the expression of an allele depends on whether it is inherited from the male or female parent
- certain genes are expressed in a parent-of-origin manner
Uniparental disomy
inheriting 2 copies of a chromosome from one parent
Epigenome
Overall pattern of chromatin modifications possessed by each individual organism
detecting DNA methylation
- restriction endonucleases
- Bisulfate sequencing
- –treat DNA with bisulphate converts cytosine residues to uracil but leaves 5-methylcytosine residues unaffected; comparison of treated vs untreated sequences reveals the unmethylated Cs
detecting histone modifications
ChIP (chromatin immuno-precipitation + next gene sequencing)
- combines chromatin immunoprecipitation with massively parallel DNA sequencing to identify the binding sites if DNA-associated proteins
methylated DNA is precipitated using an antibody that binds methylated DNA called MeDIp (methylated DNA immunoprecipitation)
Which of the following is true of CpG Islands?
a. they are methylated near promoters of actively transcribed genes
b. they are unmethylated near promoters of actively transcribed genes
c. Acetylation of CpG islands leads to repression of transcription
d. CpG islands code for RNA molecules that activate transcription
b. they are unmethylated near promoters of actively transcribed genes
Which is not a major mechanism of epigenetic change?
a. DNA methylation
b. Alteration of a DNA base sequence in a promoter
c. Histone acetylation
d. Action of RNA molecules
b. Alteration of a DNA base sequence in a promoter
Which is a characteristic of paramutation?
a. one allele is able to alter another allele when both are present in a heterozygote
b. altered alleles must be passed on to future generations
c. altered alleles must be capable of altering other alleles in future generations
d. all of the above
d. all of the above
What degree differences would you expect to see in the DNA base sequences and epigenetic marks of monozygotic twins?
a. similar differences in DNA base sequence and epigenetic marks
b. greater differences in DNA base sequence than epigenetic marks
c. Greater differences in epigenetic marks than DNA base sequence
d, no differences in either DNA base sequence or epigenetic marks
c. Greater differences in epigenetic marks than DNA base sequence
What would be the effect of introducing into a female cell siRNAs that degrade Xist RNA?
No Xist RNA would be present to coat the X chromosome, and I inactivation would not occur. Both X chromosomes would remain active
What is true of genomic imprinting?
a. the sex of the parent that transmits an allele effects the expression of the allele in the offspring
b. the sex of the offspring affects the expression of an allele inherited from one of the parents.
c. the sex of the parent affects how an allele is transmitted to the offspring
d. the sex of the offspring affects which allele is inherited from the parent
a. the sex of the parent that transmits an allele effects the expression of the allele in the offspring
civilization diseases
chronic metabolic and degenerative disorders and diseases that are initiated and/or influenced by non-optimal epigenomic programming
- often takes place early in life
Pathways that are altered by epigenetic reprogamming result in what?
disregulation of important physiological functions
ChIP-Seq
chromatin immuno-precipitation + next gene sequencing
- combines chromatin immunoprecipitation with massively parallel DNA sequencing to ID the binding sites of DNA-associated proteins
- methylated DNA is precipitated using an Ab that binds methylated DNA called MeDIp (methylated DNA immunoprecipitation)
List 3 molecular mechanisms that alter chromatin structure
1) changes in patterns of DNA methylation
2) chemical modification of histone proteins
3) RNA molecules that affect chromatin structure and gene expression
What are the 4 types of histone modifications?
- Phosphates
- Methyl groups
- Acetyl groups
- ubiquitin
When one of the two X chromosomes in somatic cells in mammalian females are randomly inactivate during development, what is the highly condensed structure called?
“Barr” body
