Day 2 Chromosomal Anomalies 3

Question 1

1. Understand the concept of imprinting and methylation.

Answer 1

Imprinting: sex-dependent epigenetic modulation of regulatory regions such as promoter sequences

If the allele inherited from the father is imprinted, it is thereby silenced, and only the allele from the mother is expressed. If the allele from the mother is imprinted, then only the allele from the father is expressed

Imprinting helped to explain how two patients with similar chromosome abnormalities could have completely different phenotypes

-expanded the idea that things other than genetic mutations have clinical consequences

Methylation:
associated with imprinting
methyl groups added to DNA, represses transcription

Reversible, post-translational modifications of histones and DNA methylation are examples of epigenetic mechanisms that alter chromatin structure, thereby affecting gene expression.

Question 2

2. Understand which main chromosomes have imprinted regions.

Answer 2

Chromosome 15 (PWS, AS)

Chromosome 11: Beckwith-Wiedemann
3 main features: Macrosomia, Macroglossia, midline abdominal defects
can develop hemihypertrophy, have increased risk of cancer

also: Russell-Silver syndrome: tiny size, short stature, mildly abnormal facial features, Vth finger clinodactyly

Chromosome 7:

less than 10% of

paternal: 1,6, 7, 11, 14, 15, 19, 20
maternal: 1, 7, 11, 14, 15, 18, 20

Question 3

3. Recognize common genetic disorders associated with imprinting.

Answer 3

Prader-Willi: deletion on paternal chromosome (15q11-13) for both PWS and angel
Angelman: deletion on maternal chromosome

PWS: maternal copy is methylated and silenced

AS: same thing, but on paternal

works cause 2 from each
(can also be caused by uniparental disomy where you get two gametes from one parent)