If a person has a total gender reassignment - (sex change) no matter how extreme the operation goes with hormone injections etc; on a DNA level, the sex of that person is absolute?

-A curious adult from Singapore

July 23, 2004

No amount of surgery, hormone injections or anything else will change someone's DNA from a man's to a woman's (or vice versa).

As you know, for humans, sex is determined by the presence of a Y chromosome -- humans with an X and a Y chromosome are male and those with two X chromosomes are female. No current (or probably future) technology can replace a chromosome in all of our trillions of cells.

What is a polymorphic micro-satellite? How can the PCR reaction help us determine if the gene is polymorphic or not?

-A curious adult from Malaysia

July 22, 2004

A micro-satellite* is a small sequence of DNA that is repeated many times. The size of the repeated sequence is usually between 1 and 4 base pairs. When the number of repeats varies between people, a micro-satellite is called polymorphic.

Micro-satellites are usually located in DNA outside of genes and are found in all sorts of plants and animals. They are useful in figuring out who the father of a child is or who committed a crime.

The DNA from a PCR reaction is then run on an agarose gel. In an agarose gel, smaller pieces of DNA run faster and so are more towards the bottom of the gel. From looking at the figure on the right, can you guess who has a copy of A and B and who has two copies of A? That's right, Bob has a copy of A and B meaning he is heterozygous for this allele. Terri has two copies of A and so is homozygous.

My husband was recently diagnosed with FH-Familial Hypercholesterolemia. I\'m concerned that the extremely high cholesterol levels will likely lead to chest pains, high blood pressure and a heart attack. Can you tell me more about FH?

-A curious adult from California

Familial Hypercholesterolemia or FH is a genetic disease where you get really high levels of the bad cholesterol, LDL. If left untreated, high levels of LDL can lead to early heart attack and stroke. (I couldn't find any evidence that high cholesterol leads to high blood pressure.)

I recently found out I was pregnant with baby#4. My first 2 children are normal, #3 was born with cystic hygroma, I am wondering if this is genetic and the possibilities of this reoccurring. Thanks.

-A curious adult from Oregon

July 20, 2004

Cystic hygromas aren't usually inherited so they aren't genetic in that sense. Most cases (60-80%) are caused by problems with chromosomes and not single genes. These chromosomal abnormalities are problems that happen during egg or sperm production and are generally random; not something that runs in families. As a mother gets older, these types of chromosomal problems increase (Down syndrome is the classic example). This may make having another baby with a cystic hygroma more likely.

I have read, \"Genetically speaking, nothing differentiates one race from another. All humans share the same set of genes. There is no African gene, no Caucasian gene, no Asian gene.\" However, I also understand that there are genetic markers such

-A curious adult from California

July 14, 2004

At the gene level, people are much more the same than they are different. In fact, individual humans vary between each other much less than do individuals of almost any other species. All of this argues that we came from a small group of common ancestors in the recent past.

I have heard a lot about Down syndrome and chromosome 21. I have also heard a lot about chromosome 21 and Alzheimer\'s. Is there any correlation between Alzheimer\'s and Down syndrome? Isn\'t chromosome 21 the chromosome that is duplicated when some

-A curious adult from Michigan

July 13, 2004

You are right, both Alzheimer's and Down syndrome have been linked to chromosome 21. As you probably know, chromosomes have lots of genes, many of which can cause disease when mutated. Chromosome 21, which has around 225 genes, is involved in many diseases.

Alzheimer's and Down syndrome are caused by different changes in chromosome 21. Down syndrome is caused when some or all of chromosome 21 is duplicated. The Alzheimer's link is to a single gene, APP, found on chromosome 21.

Eye color against the rules 1

Curious adults from California, Pennsylvania, Kentucky, and the United Kingdom

July 2, 2004

These are excellent questions. People are often very confused by eye color genetics because reality seems to fly in the face of the simple genetics we are taught in school.

What we are taught in high school biology is generally true, brown eye genes are dominant over green eye genes which are both dominant over blue eye genes.  However, because many genes are required to make each of the yellow and black pigments, there is a way called genetic compensation to get brown or green eyes from blue-eyed parents.

Now imagine that when his sperm is being made, the middle part of the eye color gene is switched between the two genes resulting in one brown eye gene and one blue eye gene with two mutations.  Now dad can produce a brown-eyed child.  (Again, the same argument works for a green eye gene as well.)

Another way to get brown eyes from blue-eyed parents is for something in the environment to affect the eye color gene.  Even though there are well-documented cases in which this happens, the reasons for it are pretty poorly understood.  

I have had two miscarriages in a row and am worried. I am a 35-year-old female with no genetic family history problems. My partner has no genetic family history problems either. I have a 10-year-old normal boy by my first marriage, and a normal 3-y

-A curious adult from Florida

June 22, 2004

If I read your questions correctly, you are mostly worried about having another miscarriage after having had two possibly Turner's syndrome related miscarriages in a row. Odds are, based on the evidence that you've presented and what I know about Turner's syndrome, you are not any more likely to have a Turner's syndrome related miscarriage because of what happened.

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