Questions and Answers
In genomic imprinting, which of the following can be imprinted?
What is the molecular mechanism involved in genomic imprinting?
What happens to the methylation pattern in gamete-forming cells?
What is the function of the imprinting control region (ICR)?
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What is the effect of methylation on gene expression?
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In which species has genomic imprinting been observed?
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What is the main function of the Xic during X-chromosome inactivation?
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What is the process by which the imprint is established during gametogenesis?
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Which type of genes are expressed in the somatic cells of adult female mammals despite being on the inactivated X chromosome?
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What is the main characteristic of genomic imprinting?
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Which of the following is NOT a stage of genomic imprinting?
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What is the result of genomic imprinting on the Igf2 gene?
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What is the effect of an Igf2 gene mutation on the size of a mouse?
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During which stage of development is the imprint pattern maintained?
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Which allele is transcribed into RNA in the Igf2 gene?
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What is the result of genomic imprinting in the Igf2 gene?
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What happens to the maternal Igf2- allele after fertilization?
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In which cells is the imprint erased?
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What is the term used to describe the expression of either the maternal or paternal allele, but not both?
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What is the term used to describe the phenomenon of a segment of DNA being marked and the effect being maintained throughout the life of the organism inheriting the marked DNA?
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What is the result of genomic imprinting in the female mouse?
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What is genomic imprinting an example of?
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Study Notes
Genomic Imprinting
- Genomic imprinting occurs in several species, including insects, mammals, and flowering plants.
- It can involve a single gene, a part of a chromosome, an entire chromosome, or even all the chromosomes from one parent.
- Genomic imprinting can be used for X inactivation in some species.
Imprinting and DNA Methylation
- Genomic imprinting involves a marking process at the molecular level.
- The imprinting of several genes involves an imprinting control region (ICR) located near the imprinted gene.
- The ICR is methylated either in the oocyte or sperm, but not both.
- The ICR contains binding sites for one or more transcription factors that regulate the imprinted gene.
- For most genes, methylation causes inhibition of transcription.
Pattern of Methylation
- Each parent inherits one methylated and one unmethylated gene, which is maintained in somatic cells.
- Methylation is removed in gamete-forming cells.
X-Chromosome Inactivation
- The inactivated X chromosome is maintained as such during subsequent cell divisions.
- Some genes on the inactivated X chromosome are expressed in the somatic cells of adult female mammals.
- Dosage compensation is unnecessary for these genes because they are located on both the X and Y chromosomes.
- Up to a quarter of X-linked genes in humans may escape full inactivation.
Genomic Imprinting
- Genomic imprinting is a phenomenon in which a segment of DNA is marked, and the effect is maintained throughout the life of the organism.
- The offspring expresses either the maternally-inherited or the paternally-inherited allele, but not both (monoallelic expression).
Mouse Igf2 Gene as an Example of Genomic Imprinting
- The Igf2 gene codes for a growth hormone called insulin-like growth factor 2.
- A functional Igf2 gene is necessary for normal size.
- Imprinting results in the expression of the paternal but not the maternal allele.
- The paternal allele is transcribed into RNA, while the maternal allele is not transcribed.
Stages of Imprinting
- Imprinting can be divided into three stages:
- Establishment of the imprint during gametogenesis
- Maintenance of the imprint during embryogenesis and in adult somatic cells
- Erasure and reestablishment of the imprint in the germ cells
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Description
This quiz covers the concept of genomic imprinting in various species, including its involvement in DNA methylation and X inactivation. Learn about the different levels of genomic imprinting, from single genes to entire chromosomes.
