Question

The genome of an organism is its total genetic material. What aspects of the genome can and cannot be determined through karyotyping?

Answer 1

 Best Answer:  A karyotype is an actual photograph of the chromosomes from one cell. Karyotypes are usually done using blood cells, fetal skin cells (from amniotic fluid or the placenta) and occasionally bone marrow cells. While a karyotype is used to confirm that a person has Down syndrome due to an extra chromosome number 21, it actually gives much more information. 

From a patient’s perspective, a karyotype is a simple blood test. But what happens to the blood after it is collected is actually quite complex. This step by step guide will help you understand why it takes so long (up to a week) to get karyotype results. 


GENETIC DISORDERS 
What a karyotype tells us 

Karyotype analysis determines the number of chromosomes in the cells and whether there are any pieces of chromosomal material that are missing, extra, or rearranged. Any variation from the normal chromosome number and arrangement can have implications for a person's fertility and the risk for having a baby with birth defects. The following chromosomal conditions can be detected by karyotype analysis: 



Down syndrome (an extra 21 chromosome) 

Turner syndrome (females with only one X chromosome) 

Klinefelter syndrome (males with two X chromosomes and a Y chromosome) 

Other sex chromosome conditions, such as XXX or XYY 

Any other aneuploidy, which is an extra or missing single chromosome 

Triploidy, which is an extra set of chromosomes, so there are three of each and 69 total 

Mosaic chromosome conditions, in which a portion of the cells show an abnormal number or arrangement of chromosomes and a portion show a normal number and arrangement 

Translocations, which are rearrangements of the chromosome material 

Large missing or extra pieces of chromosome material that are visible under a microscope 



What a karyotype cannot tell us 

There are many genetic conditions that are the result of single gene mutations. Additionally, there are many genetic conditions that are caused by multiple genes interacting. These conditions cannot be detected by chromosome analysis. Examples of conditions that cannot be detected by karyotyping are: 



Very small deletions of the chromosomal material 

Very small duplications of the chromosomal material 

Some very subtle chromosome rearrangements 

Cystic fibrosis 

Tay-Sachs disease 

Sickle cell disease 

Dwarfism 

Breast cancer 

Cleft lip/palate 

Heart defects 

These are only a few examples. The complete list would contain thousands of genetic conditions that cannot be detected by chromosome analysis.