15 Questions
What is genomic imprinting?
A phenomenon where genes show different expression patterns depending on the parent they come from
What occurs when one allele is imprinted/methylated/inactivated and the other allele is deleted?
Clinically significant conditions will arise
What happens to imprint genes in germ cells?
They are readjusted and the zygote is re-imprinted
Why are some regions of the maternal and paternal genomes not functionally equal?
The gene loci in these regions show a difference in activity according to their parental origin
Which syndrome is caused by the deletion of the paternal gene on Chromosome 15?
Prader-Willi Syndrome
What is the result of imprinting as mentioned in the passage?
Differential methylation of the two gene copies dependent on the parent of origin
What is the alternate mechanism for Angelman Syndrome?
Parental uniparental disomy
In which syndrome does the condition arise from the loss of gene expression from the normally active maternal or paternal gene copy, respectively?
Angelman Syndrome
What is the consequence of uniparental isodisomy as mentioned in the passage?
Autosomal recessive condition may arise in a child even though only one of the child’s parents is a carrier of the mutation
What is Beckwith – Wiedemann Syndrome characterized by?
Fetal overgrowth syndrome with minor dysmorphisms
What may be a consequence of nondisjunction followed by loss of genetic information?
Autosomal recessive condition in a child
What are most cases of Angelman syndrome caused by?
Deletion in the maternal chromosome 15
Which syndrome is characterized by absence of speech, mild to moderate mental retardation, small hands/feet, and a dancing gait?
Angelman Syndrome
What is the term for when both inherited copies of the chromosome are not only from the same parent, but have actually originated in the same grandparent?
Uniparental heterodisomy
What can result from Meiosis I nondisjunction?
Isodisomy
Study Notes
Genomic Imprinting
- Genomic imprinting is a phenomenon where one allele is imprinted/methylated/inactivated and the other allele is deleted, resulting in the expression of only one allele.
- In germ cells, imprint genes are erased, allowing for the re-establishment of imprints in the next generation.
Imprinting Inequality
- Some regions of the maternal and paternal genomes are not functionally equal due to genomic imprinting.
- This inequality leads to differences in gene expression between the two genomes.
Syndromes
- Deletion of the paternal gene on Chromosome 15 causes Prader-Willi Syndrome.
- Angelman Syndrome can arise from the loss of gene expression from the normally active maternal gene copy, or through an alternate mechanism.
- Beckwith-Wiedemann Syndrome is characterized by overgrowth, macroglossia, and abdominal wall defects.
Consequences
- Uniparental isodisomy, where both inherited copies of a chromosome are from the same parent, can result in the loss of genomic imprinting.
- Nondisjunction followed by loss of genetic information can lead to uniparental isodisomy.
- Most cases of Angelman syndrome are caused by a deletion of the maternal gene copy on Chromosome 15.
- Prader-Willi Syndrome is characterized by short stature, muscular hypotonia, and hyperphagia.
Genetic Terms
- Uniparental isodisomy is also known as isodisomy, where both inherited copies of a chromosome are not only from the same parent but have also originated in the same grandparent.
- Meiosis I nondisjunction can result in uniparental isodisomy.
Test your knowledge on genomic imprinting and uniparental disomy. Understand the clinical significance of gene alleles inherited from parents and the conditions arising from their malfunction or deletion.
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