What will be the effect on our body if chromosome number is altered from 46?

-A high school student from Pakistan

June 3, 2004

If a body has too few or too many chromosomes, it usually won't survive to birth. Getting the number of chromosomes right is so complicated that nature often makes mistakes. Believe it or not, around 10% of sperm and 50% of eggs contain abnormal chromosomes and more than half of first trimester spontaneous abortions are due to chromosome abnormalities.

How does a paternity test work?

-A curious adult from California

June 1, 2004

Did I find my real dad? Is that really my son? Did Michael Jackson really father Billie Jean's kid? Questions like these used to be very hard to answer. In the past, people used a blood test. This might rule out that you were the father but couldn't prove that you were.

Nowadays, DNA technology is used to figure out who is the father of a child. DNA paternity testing makes it possible to determine a child's biological father to a very high degree of certainty.

What is DNA made of?

-2 middle school students from Michigan

May 28, 2004

You may have heard of the "double helix" of DNA. Double helix refers to the shape of DNA, which is a ladder-like molecule that looks like the picture to the right. In DNA, two long strands (shown in yellow) wind around each other. These strands, the backbones of the ladder, are two long chains made of phosphate molecules.

The rungs of the ladder? Well, attached to each of these phosphates is the sugar that gives DNA its name, deoxyribose.

What does DNA do?

-A middle school student from Michigan

May 28, 2004

DNA is information. Think of DNA as a collection of cookbooks that contains all the recipes for making and running living things like worms, plants, birds, and people.

Who discovered DNA? What does DNA look like? What does DNA do? How does DNA replicate?

-A middle school student from Michigan

May 28, 2004

Well, at least you don't want to know a lot! We have split your questions into four separate parts (look for the other questions in our archived list). The first question will be answered here.

Who discovered DNA?

This is a tough question because it is hard to know what people mean by DNA. Do they mean genes, or the substance DNA or chromosomes or the structure of DNA or...

Here is a brief timeline of some discoveries about DNA:

I read someplace that scientists made a mouse with two moms and no dad. Does this mean that two women can have children now?

-A curious adult from California

May 27, 2004

No, two women can't have a baby without a sperm donor. Let's look at why it worked for these mice but wouldn't work for people.

In most animals, babies are made from sperm from the father and an egg from the mother. The sperm and egg each give half of the chromosomes or DNA to the embryo. (The mother's egg also gives the rest of cellular machinery the embryo needs to develop into a baby so making a baby with two fathers is definitely NOT possible!)

Where can you find out if you have a cancer gene that goes through your family? All my family seems to be getting cancer and it doesn't seem to leave anyone out.

-A curious adult from the United Kingdom

May 26, 2004

You have a very good question, and a great place to start would be to contact a genetic counselor. Where do you find a genetic counselor? Check with your primary or OB/GYN doctor who can refer you to one of these specialists. Alternatively, you can check for a local genetic counselor at the website of the National Society of Genetic Counselors (see link below). It is important to have the support and expertise of a genetic counselor through this process.

I read someplace that scientists made a mouse with two moms and no dad. Does this mean that two women can have children now?

No, two women can't have a baby without a sperm donor. Let's look at why it worked for these mice but wouldn't work for people.

In most animals, babies are made from sperm from the father and an egg from the mother. The sperm and egg each give half of the chromosomes or DNA to the embryo. (The mother's egg also gives the rest of cellular machinery the embryo needs to develop into a baby – so making a baby with two father is definitely NOT possible!)

Besides the father, is there anyone who could take a paternity test? Maybe his brother or sister?

-A curious adult from British Columbia, Canada

May 25, 2004

The short answer is that it is possible to determine paternity without the father. You are right that the way it is done without the father is to use other relatives. Aunts, uncles, cousins, siblings and grandparents can all be used.

Everyone, except identical twins, has a unique set of DNA. DNA is made up of 4 bases or letters, A, C, G, and T. These 4 letters form the written code that makes up the DNA sequence.

In Down syndrome besides regular trisomy there is a chance of having a translocation of chromosome no.21 with chromosomes 13, 14,or 15. One of the parents can be a balanced carrier of this translocation. I read that if a father is carrier then there

May 25, 2004

Good question. I knew about translocation mutations and Down syndrome but hadn't looked into it in too much detail before.

People usually have two copies of each chromosome (except for the sex chromosomes, X and Y). About 95% of Down syndrome cases are caused by having three copies of chromosome 21, as shown in the image to the right.

A balanced carrier is someone who has the right amount of chromosome 21 but one of the pairs is stuck to another chromosome (see the image to the right). These people still have 2 copies of chromosome 21 and so don't have any Down syndrome symptoms. However, they can give their kids Down syndrome.

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