Building a Karyotype

Medical Science I

A chart that shows the size, shape and arrangement of chromosomes.

Karyotype:

What do you notice about these karyotypes?

A normal male karyotype. Notice that the 23rd pair doesn’t appear to match.In humans, the last set of chromosomes determines whether a person will be male or female. If a person received a normal “X’s” from each parent they are female. If they received an “X” from mom and a “Y” from dad, however, then they are male. Women can only donate X’s. Men can donate X or Y.

A normal female karyotype. Notice that all of the chromosomes match their partners; there are no mistakes or alterations. Each chromosome has exactly one partner, for a total of 46.

• Two chromosomes for each number• The 23rd set doesn’t match• Except for the 23rd set, the chromosomes get smaller and smaller• The chromosome contain dark bands• All of the sets are numbered except for 23• There are 46 total chromosomes

Remember:

What else do you observe on this chromosome?

All human chromosomes have 2 arms -- a short arm and a long arm -- that are separated from each other only by the centromere, the point at which the chromosome is attached to the spindle during cell division. The short arm is termed the "p arm" while the long arm of the chromosome is termed the "q arm."

The symbol "p" was chosen to designate the short arm because "p" stands for "petit", "small" in French. The letter "q" was selected to signify the long arm merely because "q" is the next letter in the alphabet.

About the chromosome

What do you think can go wrong with chromosomes?

What are chromosome abnormalities?

There are many types of chromosome abnormalities. However, they can be organized into two basic groups:

1. Numerical Abnormalities

2. Structural Abnormalities

Numerical Abnormalities:1. Monosomy- when an individual

is missing a chromosome from a pair 2. Trisomy- has more than two

chromosomes of a pair

Turner Syndrome is an example of monosomy, where the individual - in this case a female - is born with only one sex chromosome, an X.

An example of a condition caused by numerical abnormalities is Down Syndrome, also known as Trisomy 21 (an individual with Down Syndrome has three copies of chromosome 21, rather than two).

Structural Abnormalities:When the chromosome's structure is altered. This can take several forms:

Translocations: When a portion of one chromosome is transferred to another chromosome. There are two main types of translocations. In a reciprocal translocation, segments from two different chromosomes have been exchanged. In a Robertsonian translocation, an entire chromosome has attached to another at the centromere.

Robertsonian translocation

Inversions: A portion of the chromosome has broken off, turned upside down and reattached, therefore the genetic material is inverted.

Deletions: A portion of the chromosome is missing or deleted.

Duplications: A portion of the chromosome is duplicated, resulting in extra genetic material.

1.Deletion2.Duplication3.Inversion