Non-Mendelian Inheritance (Hard)

Questions and Answers

What is the function of the imprinting control region (ICR) in genomic imprinting?

To activate transcription of the imprinted gene

To bind transcription factors that regulate the imprinted gene (correct)

To methylate the imprinted gene in both oocyte and sperm

To demethylate the imprinted gene

What happens to methylation in gamete-forming cells?

Methylation is replaced by histone modification

Methylation is removed (correct)

Methylation is maintained

Methylation is inherited from the parent

What is the result of methylation on gene transcription?

Inhibition of transcription (correct)

No effect on transcription

Variable effect on transcription

Activation of transcription

What is the unit of genomic imprinting?

All of the above Signup and view all the answers

What is the purpose of genomic imprinting in some species?

X inactivation Signup and view all the answers

In which cells is the pattern of methylation maintained?

Somatic cells Signup and view all the answers

What is the main purpose of dosage compensation?

To offset differences in the number of active sex chromosomes Signup and view all the answers

What is a characteristic of epigenetic inheritance?

It is caused by chromosomal modifications Signup and view all the answers

During which stages of development can epigenetic changes occur?

During oogenesis, spermatogenesis, or early embryonic development Signup and view all the answers

What is the mechanism of dosage compensation in placental mammals?

One of the X chromosomes in females is inactivated Signup and view all the answers

What is an example of a species where the X chromosome from the male parent is inactivated?

Certain species, but not humans Signup and view all the answers

Why does dosage compensation occur?

To offset differences in the number of active sex chromosomes Signup and view all the answers

What type of modifications can cause epigenetic changes?

Chromosomal and DNA modifications Signup and view all the answers

What is the significance of epigenetic inheritance?

It does not change the DNA sequence, but alters gene expression Signup and view all the answers

What is the primary function of the Xic during X-chromosome inactivation?

To maintain the inactivated X chromosome during subsequent cell divisions Signup and view all the answers

Which of the following statements about genomic imprinting is TRUE?

It is a mechanism that ensures monoallelic expression of imprinted genes Signup and view all the answers

What is the effect of the Igf2− allele on the size of a mouse?

It causes the mouse to be smaller in size, but only if inherited from the female parent Signup and view all the answers

What is the percentage of X-linked genes in humans that may escape full inactivation?

Up to 25% Signup and view all the answers

Which of the following genes is an example of genomic imprinting in the mouse?

Igf2 Signup and view all the answers

What is the term used to describe the phenomenon of genes being expressed from only one parent?

Monoallelic expression Signup and view all the answers

What is the mechanism thought to be involved in the escape of X-linked genes from inactivation?

Loosening of chromatin in specific regions Signup and view all the answers

Which of the following is a characteristic of genomic imprinting?

It is a heritable epigenetic phenomenon Signup and view all the answers

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.