Questions and Answers
What is the function of the imprinting control region (ICR) in genomic imprinting?
What happens to methylation in gamete-forming cells?
What is the result of methylation on gene transcription?
What is the unit of genomic imprinting?
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What is the purpose of genomic imprinting in some species?
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In which cells is the pattern of methylation maintained?
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What is the main purpose of dosage compensation?
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What is a characteristic of epigenetic inheritance?
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During which stages of development can epigenetic changes occur?
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What is the mechanism of dosage compensation in placental mammals?
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What is an example of a species where the X chromosome from the male parent is inactivated?
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Why does dosage compensation occur?
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What type of modifications can cause epigenetic changes?
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What is the significance of epigenetic inheritance?
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What is the primary function of the Xic during X-chromosome inactivation?
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Which of the following statements about genomic imprinting is TRUE?
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What is the effect of the Igf2− allele on the size of a mouse?
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What is the percentage of X-linked genes in humans that may escape full inactivation?
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Which of the following genes is an example of genomic imprinting in the mouse?
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What is the term used to describe the phenomenon of genes being expressed from only one parent?
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What is the mechanism thought to be involved in the escape of X-linked genes from inactivation?
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Which of the following is a characteristic of genomic imprinting?
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Study Notes
Epigenetic Inheritance
- Epigenetic inheritance refers to a pattern in which a modification occurs to a nuclear gene or chromosome, altering gene expression, but the DNA sequence remains unchanged.
- Epigenetic changes are caused by DNA and chromosomal modifications that can occur during oogenesis, spermatogenesis, or early embryonic development.
Dosage Compensation
- Dosage compensation offsets differences in the number of active sex chromosomes.
- It has been studied in mammals, Drosophila, and Caenorhabditis elegans, with different mechanisms depending on the species.
- In placental mammals, one of the X chromosomes in somatic cells of females is inactivated, or the X chromosome from the male parent is inactivated, or either of the two X chromosomes is randomly inactivated.
Genomic Imprinting
- Genomic imprinting occurs in several species, including insects, mammals, and flowering plants, involving a single gene, part of a chromosome, an entire chromosome, or all chromosomes from one parent.
- It can be used for X inactivation in some species.
- Imprinting involves a marking process, with an imprinting control region (ICR) located near the imprinted gene, which is methylated either in the oocyte or sperm, but not both.
- For most genes, methylation causes inhibition of transcription.
Pattern of Methylation and X-Chromosome Inactivation
- Each parent inherits one methylated and one unmethylated gene, which is maintained in somatic cells, and methylation is removed in gamete-forming cells.
- The inactivated X chromosomes is maintained as such during subsequent cell divisions.
- Some genes on the inactivated X chromosome are expressed in somatic cells of adult female mammals, including pseudoautosomal genes, which do not require dosage compensation.
Genomic Imprinting and Gene Expression
- Genomic imprinting results in the expression of either the maternally-inherited or the paternally-inherited allele, but not both, a phenomenon known as monoallelic expression.
- The Igf2 gene in mice is an example of genomic imprinting, where the paternal allele is transcribed into RNA, but the maternal allele is not.
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Description
Explore epigenetic inheritance and dosage compensation, concepts crucial to understanding gene expression and chromosomal development.