biology DNA

?
  • Created by: rosemat12
  • Created on: 31-03-17 09:27

what is DNA? Gene? Chromosome? Order?

Chromosomes are X-shaped objects found in the nucleus of most cells. They consist of long strands of a substance called deoxyribonucleic acid, or DNA for short.

DNA is the complex chemical that carries genetic information.

A section of DNA that has the genetic code for making a particular protein is called a gene.

order?

Cell - Nucleus - Chromosome - DNA - Gene

1 of 4

Inheritance and chromosomes

The gene is the unit of inheritance, and each chromosome may have several thousand genes. We inherit particular chromosomes through the egg of our mother and sperm of our father. The genes on those chromosomes carry the code that determines our physical characteristics, which are a combination of those of our two parents.

In humans, each cell normally contains 23 pairs of chromosomes, for a total of 46. you get one set from your mother and one from your father. Twenty-two of these pairs, called autosomes, look the same in both males and females. The 23rd pair, the sex chromosomes, differ between males and females. Females have two copies of the X chromosome, while males have one X and one Y chromosome.

2 of 4

Alleles

Different forms of the same gene are called alleles. You inherit one allele for each gene from your father and one allele for each gene from your mother.These alleles determine your physical characteristics. the characteristics you get from your patrents will depend on the combination of your alleles.

recessive allele only shows if the individual has two copies of the recessive allele. For example, the allele for blue eyes is recessive. You need two copies of the allele to have blue eyes.

dominant allele always shows, even if the individual only has one copy of the allele. For example, the allele for brown eyes is dominant. You only need one copy of the allele to have brown eyes (and two copies will still give you brown eyes).

3 of 4

genetic disorders

Some diseases are inherited from our parents through our genes: they are called genetic disorders. They occur because of faulty alleles. Cystic fibrosis is an example of a genetic disorder.

People with cystic fibrosis have inherited two faulty alleles, one from their father and one from their mother. They produce unusually thick and sticky mucus in their lungs and airways. Their lungs become congested with mucus, and they are more likely to get respiratory infections.

It is hoped that it may one day be possible to repair the faulty alleles using gene therapy, perhaps by putting the normal allele into the cells of the lungs. This would greatly improve the lives of people with cystic fibrosis, who often need lung transplants as their illness progresses.

Members of some families are particularly at risk of developing certain types of breast cancer, because they carry faulty alleles. These alleles have been identified, and it is now possible to test people to see if they have an increased risk of developing breast cancer. This allows them to make decisions, if they wish, about whether to have surgery to remove breast tissue before any cancer develops in their breasts.

4 of 4

Comments

No comments have yet been made

Similar Biology resources:

See all Biology resources »See all DNA and inheritance resources »