Tuesday, January 30, 2007

Hairy Earlobes and the Y Chromosome

Scientists close to deciphering Y chromosome: Will it finally get

The article can be found at this web site:

Description of David Page research on the Y chromosome: www.hhmi.org/science/genetics/page.htm

Progress on sequencing chromosomes: http://www.ncbi.nlm.nih.gov/Genomes/

Common ancestor for male Y chromosome: http://haplogroup-a.com/Ancient-Root-AJHG2013.pdf

11 Facts about the Y Chromosome: http://www.genome.gov/27561885

Thursday, January 25, 2007

Extra Credit Article - 3rd Marking Period - Sex-Linked Diseases

Hand-Write 20 Facts, in complete sentences, on loose leaf.

Web address: http://www.sciencedaily.com/releases/2006/03/060322184446.htm

Source: JAMA and Archives Journals
Date: March 23, 2006
More on: Genes, Brain Tumor, Immune System, Diseases and Conditions, Stem Cells, Pregnancy and Childbirth

X Chromosomes Key To Sex Differences In Health
Science Daily — Females have two X chromosomes and males only have one--and this simple fact, along with the occurrence of what geneticists call mosaicism, may not only explain why women are less susceptible than men to certain genetic diseases, but also may account for the female prevalence in the incidence of other conditions and even sex differences in behavior, according to a special communication in the March 22/29 issue of JAMA, a theme issue on women's health.

Author Barbara R. Migeon, M.D., of The Johns Hopkins University School of Medicine, Baltimore, presented the article today at a JAMA media briefing on women's health in New York.

Women's diseases have typically been thought to involve female reproductive organs and hormones, Dr. Migeon writes. However, researchers have begun to recognize that diseases may be expressed differently in men and women, and that not all of the differences can be explained by hormones alone. For instance, male infants have a greater death rate than females and are more susceptible to infections, such as meningitis.

The sex chromosomes, known as X and Y, determine the sex of a child and may also offer additional explanations for sex differences in disease, Dr. Migeon writes. Females are born with two X chromosomes, one from each parent, and males inherit one X chromosome from their mothers and one Y chromosome from their fathers. More than 1,000 genes reside on the X chromosome and are therefore known as X-linked genes, she continues. In contrast, the Y-chromosome carries the instructions for male development and little else--probably fewer than 100 genes in all--and lacks working copies of many of the X-linked genes.

"Having only one copy of X-linked genes (one allele) makes males more vulnerable to deleterious mutations that adversely affect the function encoded by these genes, certainly more vulnerable than females with two copies (two alleles)," Dr. Migeon writes. "If his mutated allele is defective, a male cannot perform the function encoded by that gene. Yet the same mutated allele is usually less deleterious to a female, because she has a normal functioning copy (on the other X chromosome). This is why so many male-only diseases are attributable to defective genes on the X chromosome." Such diseases include Duchenne muscular dystrophy, hemophilia and Hunter syndrome, which causes dwarfing, abnormal bones and mental retardation in males but usually does not affect females who carry the same mutated gene.

This duplication of genes is generally advantageous to women, but is not as straightforward as having two copies of each gene to men's single copy. Only one copy of each X-linked gene can be expressed, or turned on, in each individual cell in a woman's body. This process of turning one chromosome on and the other off, known as X inactivation, occurs randomly as the female embryo develops. Because it happens in every cell, a woman usually ends up with a mixture of cells within the same tissue, some expressing genes inherited from her mother and some those from her father. Therefore, geneticists say that females are mosaics. "The bottom line is that although females have only a single working set of X-linked genes in each cell, they have a backup copy in reserve," Dr. Migeon writes. Also, even if some cells in a woman's body express mutated X-linked genes associated with genetic diseases, other cells usually express the normal gene, overriding or mitigating the effect of the mutation.

Mosaicism explains not only why some genetic diseases occur exclusively in males but also why some are female-specific. Some X-linked gene mutations may be so detrimental that males who carry them die before birth or shortly after. Women may still be affected by these mutations, but because they balance the defective genes with unaffected copies their symptoms are less severe, Dr. Migeon writes. For example, males with a genetic disorder known as incontinentia pigmenti usually die in utero, while females affected by the same mutation develop abnormalities in hair, teeth and skin. Mosaicism also leads to differences among females with such diseases; because women can have different ratios of cells expressing mutated and non-mutated genes, the conditions can manifest and progress at varying rates and with different symptoms.

Genetic diseases are not the only ones affected by mosaicism, Dr. Migeon explains. For example, autoimmune disorders such as thyroiditis and scleroderma, which occur when the body attacks its own tissues, are more common in women than men. If the ratio of X-linked genes from a woman's mother and father is drastically skewed in her cells, which could occur by chance or if cells expressing genes on one X chromosome have a growth advantage over the cells expressing the other X, some X-linked genes would be expressed in relatively few cells. This might increase the chance that immune cells in the body fail to protect these tissues from attack.

These differences in the expression of X-linked genes have the capability to affect many other processes in the body as well. "It is likely that the contribution of cellular mosaicism to sex differences is not limited to disease," Dr. Migeon writes. "Recent studies have shown that sex affects the way a person's brain responds to humor. It does not seem far-fetched to think that cellular mosaicism may have a role in some of these sex differences in behavior."

(JAMA. 2006;295:1428-1433. Available pre-embargo to the media at www.jamamedia.org)

Note: This story has been adapted from a news release issued by JAMA and Archives Journals.

Wednesday, January 24, 2007

New Jersey Meteorite

A metal object, which later was identified as a meteorite, is held by Freehold Township Police Lt. Robert Brightman during a news conference Jan. 3. No one was injured when the object crashed through the roof of the township home of Srinivasan and Shankari Nageswaran.


Meteor that crashed through house to go on display in N.J.
Associated Press
Posted Wednesday, January 24, 2007 at 2:32 pm
NEW BRUNSWICK, N.J. — It caused a sensation earlier this month when it crashed through the roof of a Freehold Township family's home, landing in the bathroom.

Now members of the public will have a chance to catch a glimpse of the golf ball-sized, silvery meteorite that came to the Garden State from outer space, Rutgers University announced Wednesday.

Rutgers' geology museum in New Brunswick plans to hold a one-day display of the meteorite during its annual open house, scheduled for Saturday. Admission is free.

Two geologists from Rutgers, along with an independent metallurgist, helped Freehold Township police and the homeowners, the Nageswaran family, identify the golf-ball-sized, 13-ounce object as a metal-rich meteorite, possibly from the deep interior of a broken-up asteroid.

The Nageswarans recently said they were still deciding what to do with their meteorite, but wanted it to serve an educational purpose.

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Saturday, January 20, 2007

What is a Dichotomous Key?

For students who were absent for the lesson on Making A Dichotomous Key, here is a web site that has an alternative lesson. Print out lesson 5es: Creating and Using A Dichotomous Key. Print out Butterflies to Key. Print out Butterfly Key Worksheet. Print out Butterfly Key Flow Chart. http://oceanica.cofc.edu/LoggerheadLessons/IdentificationHome.htm

See my 2/24/2009 post for more web sites on dicotomous keys:

Wednesday, January 17, 2007

Extra Credit Opportunity

Ancient Skull Has both Neanderthal, Modern Characteristics

You can visit this link:

and write 20 facts (complete sentences) from this article, or any of the related articles that are listed with it.

Thursday, January 11, 2007

Middletown Comet Sighting

Comet seen over Delaware

Reader submits photo taken from Middletown

The News Journal

Updated Thursday, January 11, 2007 at 6:29 pm

Comet McNaught as viewed from the Middletown area.

Submitted photo/ROBERT SLOBINS
Reader Robert Slobins submitted this photograph of Comet McNaught, which he says “is the fourth brightest comet since 1935.”

“I photographed this comet from Middletown as it was setting yesterday. This is a naked-eye object now, and may be visible in broad daylight this weekend as it rounds the sun,” Slobins said.

“Extreme caution is advised when one does this; please refer to web sites like www.space.com, www.spaceweather.com, or www.SkyandTelescope.com for more details on this.

“It is, by far, best to hide the sun behind a building or wall so as not to permit sunlight to fall on the face while trying to find the comet.

According to the spaceweather.com Web site, the comet is visible in the western sky, low and to the right of Venus, and a clear view of the horizon is needed to see it.

Slobins, 53, a Newark-area resident, says he’s been interested in comets since he was 5.

He took the photograph from a spot off Del. 15.

“That tail is made up of stuff that is as dark as copier toner. If it were fully reflective. it would shine just as bright as the sun itself,” said Slobins.

In the next few days, the comet will pass between the sun and Earth. leading to forward-scattered light, he said. “The light bounces off the dust and makes the comet appear even brighter to be visible during the daytime.”

This weekend’s weather may not be clear enough for a good look, though, he said.