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.

I read from an article that many bony fish which include Nemo, the clownfish, change sex throughout their life-spans. How does changing sex impact their DNA? Were they born with both X and Y chromosomes or somehow they were changed when the sex wa

-A curious adult from California

June 25, 2004

It is amazing the variety of ways Mother Nature has come up with to determine whether an animal is going to have a boy or a girl. 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.

I have a bunch of questions about genes, their locations on chromosomes, and \"junk\" DNA. Do genes on one chromosome have some functional characteristic or are genes scattered across chromosomes without regard to their function? How important is

-A curious adult from California

June 16, 2004

First off, it doesn't really matter on which chromosome a gene is located. The best evidence for this is found by comparing mouse and human chromosomes. What you can quickly see is that at a high level, mouse chromosomes are really just mixed up bits of human chromosomes. In other words, you can mix and match parts of chromosomes and everything works out OK.

How does DNA replicate itself?

-A middle school student from Michigan

June 14, 2004

Cells need to copy their DNA when they divide. This process is called DNA replication. To understand how DNA is copied, we first need to understand the structure of DNA.

DNA is made of two long strands that wrap around each other to make the famous double helix. Each strand is composed of a sequence of molecules called nucleotides. Bases are a part of the nucleotides.

The other night on CSI they used a medical term (I think it started with a C) for a person that had two different DNA\'s. Have you ever heard of this?

-A curious adult from Alabama

June 8, 2004

What you are thinking of is "chimera." In the TV show, CSI, a woman claimed a man raped her, but DNA taken from his blood did not match the DNA of the suspect. The test also revealed that the most likely suspect was a relative of the man. When further DNA tests cleared his relatives, the man's DNA was tested again. This time it was from a hair sample and this time it was a perfect match to the suspect's DNA. Can one person have two types of DNA in different parts of his body?

What is the difference between dominant vs. recessive? Can you tell me what I could do to show my class about this without this being long?Thank you.

-A middle school student from New York

June 4, 2004

Good question. Remember that for most genes, you have two copies of each gene that you inherited from your mother and your father.

Each copy of the gene could be different. For example one copy may give you blue eyes while another may give you brown.

So, what color are your eyes if you have both the brown and blue eye version of the eye color gene? Brown. This is where the idea of dominant and recessive comes in.