Suppose an X-linked gene in mice exists as two alleles, B and b. X-chromosome inactivation, a process in which one X chromo- some is turned off, occurs in the somatic cells of female mammals (see Chapter 5). Allele B encodes an mRNA that is 900 nucleo- tides long, whereas allele b contains a small deletion that shortens the mRNA to a length of 825 nucleotides. Draw the expected Northern blot that will be obtained using mRNA isolated from so- matic tissue of the following mice: Lane 1. mRNA from an XºY male mouse Lane 2. mRNA from an XX¹ female mouse Lane 3. mRNA from an XBX¹ female mouse Note: The sample taken from the female mouse is not from a clone of cells. It is from a tissue sample, like that shown at the beginning of the experiment in Figure 5.6.

Suppose an X-linked gene in mice exists as two alleles, B and b. X-chromosome inactivation, a process in which one X chromo- some is turned off, occurs in the somatic cells of female mammals (see Chapter 5). Allele B encodes an mRNA that is 900 nucleo- tides long, whereas allele b contains a small deletion that shortens the mRNA to a length of 825 nucleotides. Draw the expected Northern blot that will be obtained using mRNA isolated from so- matic tissue of the following mice: Lane 1. mRNA from an XºY male mouse Lane 2. mRNA from an XX¹ female mouse Lane 3. mRNA from an XBX¹ female mouse Note: The sample taken from the female mouse is not from a clone of cells. It is from a tissue sample, like that shown at the beginning of the experiment in Figure 5.6.

Human Heredity: Principles and Issues (MindTap Course List)

11th Edition

ISBN:9781305251052

Author:Michael Cummings

Publisher:Michael Cummings

Chapter7: Development And Sex Determination

Section: Chapter Questions

Problem 19QP: Equalizing the Expression of X Chromosome Genes in Males and Females Individuals with an XXY...

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Occasionally, a mouse X chromosome is broken into two pieces and each piece becomes attached to a different autosome. In this event, the genes on only one of the two pieces undergo X inactivation. What does this observation indicate about the mechanism of X-chromosome inactivation?
In the Fast Forward Box Visualizing X Chromosome Inactivation in Transgenic Mice, suppose the investigators had looked at the expression of green and red fluorescent protein in early mouse embryos, when the embryos have fewer than 500 cells. What patterns would they likely have observed?
Explain about how X chromosome inactivation takes place in mammals at the chromosomal and molecular level. B. What genes are involved in inactivating a human X chromosome? . C. What role does X chromosome-specific inactivating transcript --XIST-- non coding RNA play in the inactivation of the human X chromosome.
Gunter Korge examined several proteins that are secreted from the salivary glands of Drosophila melanogaster during larval development (G. Korge. 1975. Proceedings of the National Academy of Sciences of the United States of America 72:4550–4554). One protein, called protein fraction 4, was encoded by a gene found by deletion mapping to be located on the X chromosome at position 3C. Korge observed that, about 5 hours before the first synthesis of protein fraction 4, an expanded and puffed-out region formed on the X chromosome at position 3C. This chromosome puff disappeared before the end of the third larval instar stage, when the synthesis of protein fraction 4 ceased. He observed that there was no puff at position 3C in a special strain of flies that lacked secretion of protein fraction 4. Explain these results. What is the chromosome puff at region 3, and why does its appearance and disappearance roughly coincide with the secretion of protein fraction 4?
Figure 19.25 shows that the Sxl protein binds to the mRNA of the msl-2 gene, inhibiting translation of the mRNA’s proper reading frame. The MSL-2 protein is a transcription factor that binds to the X chromosome in XY males to double the level of X-linked gene transcription, thus equalizing X-linked gene expression in XY males and XX females. a. In which sex, XY males or XX females, would the Sxl protein bind to the msl-2 mRNA? b. As discussed in Problem 35, some Sxl alleles are lethal to females and others are lethal to males. Is the function of Sxl in regulating the synthesis of Msl-2 protein sufficient to explain the sex-specific lethality caused by both kinds of alleles? c. Predict the effect of loss-of-function mutations in msl-2 on male and female fertility and viability.
For the Igf2 gene, where do de novo methylation and maintenancemethylation occur?a. De novo methylation occurs in sperm, and maintenancemethylation occurs in egg cells.b. De novo methylation occurs in egg cells, and maintenancemethylation occurs in sperm cells.c. De novo methylation occurs in sperm, and maintenancemethylation occurs in somatic cells of offspring.d. De novo methylation occurs in egg cells, and maintenancemethylation occurs in somatic cells of offspring.
Following X-chromosome inactivation, most of the genes on theinactivated X chromosome are silenced. Explain how. Name onegene that is not silenced.
In the Fast Forward Box Visualizing X ChromosomeInactivation in Transgenic Mice, suppose the investigators had looked at the expression of green and red fluorescent protein in early mouse embryos, when theembryos have fewer than 500 cells. What patterns wouldthey likely have observed? (Assume that the transgenesmake gene product this early in development.)
Q. Both histone deacetylase (HDAC) and Xist would be on a list of genes involved in X chromosome inactivation. In which of the following ways would the histone deacetylase gene be similar to the Xist gene? A. They would both be transcribed. B. They would both be translated. C. They would both undergo intron splicing. D. They would both be transported to the cytoplasm after transcription.
In humans, dosage compensation is accomplished by: inactivating one X chromosome in female somatic cells inactivating one homolog from each homologous pair of chromosomes in female somatic cells inactivating the Y chromosome in male somatic cells increasing gene expression from the X chromosome in male somatic cell
. Early in development, most human cells turn off expression of an essential component of telomerase, the enzyme responsible for addition of telomere repeat sequences (5’-TTAGGG) to the ends of chromosomes. Thus, as our cells proliferate their telomeres get shorter and shorter, but are normally not lost over the course of a lifetime. If cells are removed from the body and grown in culture, however they ultimately enter a state of replicative senescence and stop dividing when their telomeres get too short. By contrast, most human tumor cells express active telomerase, allowing them to maintain their telomeres and grow beyond the normal limit imposed by senescence - good for them, bad for us. Anticipating a universal cure for cancer, you set up a company to screen chemical ‘libraries’ for telomerase inhibitors. The company share price takes a dive, however, when a rival group generates a strain of telomerase-knockout mice. These mice breed happily for several generations, but…
Gunter Korge examined several proteins that are secreted from the salivary glands of Drosophila melanogaster during larval development . One protein, called protein fraction 4, was encoded by a gene found by deletion mapping to be located on the X chromosome at position 3C. Korge observed that, about 5 hours before the first synthesis of protein fraction 4, an expanded and puffed-out region formed on the X chromosome at position 3C. This chromosome puff disappeared before the end of the third larval instar stage, when the synthesis of protein fraction 4 ceased. He observed that there was no puff at position 3C in a special strain of flies that lacked secretion of protein fraction 4. Explain these results. What is the chromosome puff at region 3, and why does its appearance and disappearance roughly coincide with the secretion of protein fraction 4?