imprinting (6)

Question 1

define imprinting

Answer 1

differential modification of the maternal & paternal genetic contributions to the zygot resulting in the differential expression of parental alleles during development and in the adult

Question 2

what are 2 examples of DNA methylation

Answer 2

X inactivation

imprinting

Question 3

tell me about meiotic imprinting

Answer 3

although it is acceptable for somatic cells to be a mosaic female & male imprinted chromosome, it is essential that the single correct imprint (male OR female) be transmitted to the offspring
–so it is known that one of the functions of meiosis is to “reimprint” all of the chromosomes that will end up in gametes

Question 4

what is an imprinting failure that can occur in meiosis

Answer 4

some chromosomes for a male could retain the female methylation pattern causing the offspring to have 1 chromosome from each parent, but both the chromosomes will have female imprinting

Question 5

what is uniparental disomy?

Answer 5

inheritance of a chromosome of chromosomes form 1 parent to the exclusion of the other parent.

Question 6

what type of technology is used to determine if a UPD is present?

Answer 6

NOT karyotype

molecular probe technology can be used

Question 7

what is uniparental heterodisomy? how does it occur?

Answer 7

• 2 diff chromosomes form the same parent
• If the cell has trisomy which is not compatible with life- it can be corrected by “loosing” one of the chromosomes and 1/3 of the time the chromosome lost is the only 1 from the other parent and the two left are from the same parent

Question 8

what is uniparental isodisomy? how does it happen?

Answer 8

duplication of 1 chromosome from 1 parent
-The cell senses that there has been a problem (ie. A deletion/nondisjunction) and the cell then duplicates the monosome (the only chromosome) that it has- this is called “zygote rescue”

Question 9

what chromosome is the problem with prander willi & angelman syndromes?

Answer 9

proximal long arm of chromosome 15

Question 10

what chromosome is NOT present in PWS?

Answer 10

15 from dad

Question 11

what chromosome is NOT present in AS?

Answer 11

15 from mom

Question 12

what disease does the following describe:
“Patients are small & hypotonic at birth but change within 1st year of life and begin to gain weight rapidly. It not placed on controlled diet can become obese”

Answer 12

prader wili syndrome

Question 13

describe some symptoms of AS

Answer 13

• Most common mutation is in the UBE3A gene?
• Severely mentally retarded, friendly but normally cannot carry on conversations and often have bursts of laughter
• Hyperactivity, short stature, microcephaly, seizures and ataxia

Question 14

is cytogenetics better for detecting AS or PWS?

Answer 14

PWS detected in 60-65%

only 10-20% of AS cases

Question 15

in paternal imprinting, what genes are active/inactive?
UBE3A
SNRPN
necdin

Answer 15

UBE3A: inactive
SNRPN: active
necdin: active:

Question 16

in maternal imprinting, what genes are active/inactive?
UBE3A
SNRPN
necdin

Answer 16

UBE3A: active
SNRPN: inactive
necdin: inactive

Question 17

what is epigenetics?

Answer 17

the study of heritable changes in gene function that are NOT caused by change in DNA sequence

Question 18

what are 3 primary categories of epigenetic modification?

Answer 18

1. DNA methylation
2. histone modification
3. chromatin remodeling

Question 19

what is microRNA?

Answer 19

• small non coding RNAs
• miRNAs bind to mRNA to regulate gene expression
• can prevent translocation or interfere with the translocation process

Question 20

tell me about the MECP2 gene mutation in Rett Syndrome

Answer 20

• MECP2: located on the distal long arm of X chromosome so subject to X inactivation
• Normal function required for maturation of neurons & normal development
• Ranging phenotypes depending on how many cells have the mutation on the active X
• This mutation can be lethal in males who only have 1 x chromosome

Question 21

what are the 3 genetic mechanisms that can cause PSW or AS

Answer 21

1. Deletion of paternal/maternalchromosome 15
2. Maternal/paternal uniparental disomy
3. An imprinting error