Karyotype Testing

KARYOTYPING AND GENETICS TESTING INSTRUCTIONS

Introduction:

In the chromosome labs, we used a simulation and defined what a chromosome is, and we took a look at its structure and the copying and distribution of chromosomes during cell division. We also considered some genetic abnormalities resulting from the non-disjunction or inability of chromosomes to segregate properly during cell division.

In this lab, we want to take a closer look at human chromosomes and the concept of non-disjunction by looking at actual photos of human chromosomes. These photos are called karyotypes and these are used in clinical medicine. Karyotypes from a single cell are used in the hospital clinic to determine genetic abnormalities due to non-disjunction. Samples are taken from parents or unborn children and cells are cultured (grown in the lab) and then analyzed to see if the full complement of chromosomes are in each cell. Here is a quote from a fertility clinic website describing the karyotyping procedure:

A karyotype can be performed on any tissue but most often it is done from a blood sample, a sample of amniotic fluid or a piece of placenta obtained through chorionic villi sampling. Karyotyping is a complex process that involves growing the cells, obtaining the chromosomes, staining and analyzing the chromosomes and reporting the results. A karyotype is an actual photograph of the chromosomes from one cell.

Why do the cells have to be cultured? Think about it and see the answer at the bottom of page 2. Since in some cases individual genetic abnormalities are due to non-disjunction of certain chromosomes, each of the 23 pairs of chromosomes is observed so that abnormalities can be detected. A complete set of chromosomes is determined by locating each pair of the 23 chromosomes. How can this be done if they all look the same? They can be the same because each pair of chromosomes is actually very different from all other pairs. For instance, chromosomes can differ in appearance by their length, the position of their centromere, and their banding pattern. The banding pattern on a chromosome is a series of stripes seen on chromosomes and is the result of the way the DNA is packed into the chromosome. Chromosome pairs show identical (or nearly identical) banding patterns. In this activity, you will be completing an actual karyotype by observing and arranging chromosomes in clinically-derived karyotype samples.

Reading:

Lewis text: chs. 13, 2021 (Section 21.3)

Activity:

Proceed to this website (below). Read the Introduction and Patient Histories, then complete the karyotypes. After you successfully complete them, you will be asked to choose the genetic abnormality present in the patient sample. Write down your answers and then answer the questions below in the fill-in-the-blank problem section.

http://www.biology.arizona.edu/human_bio/activities/karyotyping/patient_a/patient_a.html

Assessment: 

Each of the following questions involves a single-word answer or number answer. Upload your answers and number them 13.

Short Answer (30 pts):

1. According to your analysis of patient As karyotype, you believe that this patient has the genetic condition known as ________________________ 21. (1 word answer) 

2. According to your analysis of patient Bs karyotype, you believe that this patient has the genetic condition known as ________________________ syndrome. (1 word answer) 

According to your analysis of patient Cs karyotype, you believe that this patient has the genetic condition known as Trisomy _______________. (1 number answer)

Short Essay (30 pts): 

Use internet and book resources to determine the circumstances under which karyotyping is done in a health clinic setting. Also, share your thoughts regarding whether you or one of your family members would choose to undergo a karyotype test. The short essay must be 100140 words and demonstrate course-related knowledge, and it must include 1 citation from the Bible and 1 from an outside source other than your course textbook. Sources must be cited in current Turabian format. (References are not included in the final word count.)

Answer: Remember that chromosomes are only condensed in their classic X shape during cell division, so cells must be cultured or grown so that they proceed through the cell cycle. This allows the clinician to find cells with condensed chromosomes.