Essential Questions…

What is a karyotype? What can it help you determine? What does a karyotype of a human

look like?

Karyotyping Lab

50 points40 points for correct karyotype10 points questionsDue tomorrow

Objective

In this lab, you will create and analyze a karyotype of cells from a fetus to count chromosomes & determine the sex of the fetus.

What is a Karyotype?

A karyotype is made from a photomicrograph (photo taken through a microscope) of the chromosomes from a cell in some phase of meiosis.

The photographic images of the chromosomes are cut out and arranged in homologous pairs by their size and shape.

The karyotype can be analyzed to determine the sex of the individual and whether there are any chromosomal abnormalities. For example, the karyotype of a female shows two X

chromosomes, and the karyotype of a male shows an X chromosome and a Y chromosome.

A karyotype is a diagram that shows a cell’s chromosomes arranged in order from largest to smallest.

Directions

In groups of two, read through and follow directions.

Create your karyotype, analyze it, and answer the associated questions.

You will turn in: Karyotype Answers to questions One worksheet per group of two with both partn ers’ name on it.

A Common Abnormality…Down Syndrome

Trisomy is an abnormality in which a cell has an extra chromosome, or section of a chromosome. This means that the cell contains 47 chromosomes instead of 46. Down syndrome, or trisomy 21, is a chromosomal abnormality that results from having an extra number 21 chromosome. This extra chromosome means too many genes and developmental problems generally result.

A variety of developmental problems from functional (able to drive, live alone) to seriously debilitating (mental retardation that requires 24-hr monitoring) can result.

1:1000 births

Other Chromosome Anomalies Trisomy X

Three ‘x’ chromosomes Most “common” affects: Generally normal development but can be taller

and more slender (generality that can be subject to scrutiny)

Social integration difficulties. 1:1000

Turner’s Syndrome

Generally only female with only 1 ‘x’ chromosome. If the infant female survives will be underdeveloped. Usually petite (4’7” average height) 1:2000

More

Klinefelter syndrome XXY (1:500-1000) Feminized male.

Little body hair Underdeveloped male organs, little if any testosterone

production, usually infertile Supermale

XYY (1:1000) Over-developed male but otherwise normal.

Above average height (6’3” average) Extra testosterone production, excessive acne during

adolescence. Others can occur with the other chromosomes as well.

Chromosomal Abnormalities How Do They Happen?

Chromosomal abnormalities often result from nondisjunction, the failure of chromosomes to separate properly during meiosis.

Nondisjunction results in cells that have too many or too few chromosomes.

What’s the Problem?

47Chromosomes

in gamete

Procedure:Make sure to write the letter of the version of your chromosome spread on your karyotype spread!

1. READ the directions page. This is a class set so please do not take or write on this.

2. CUT OUT EACH CHROMOSOME from the chromosome spread in Figure 2. Be sure to leave a slight margin around each chromosome.

3. ARRANGE THEM IN HOMOLOGOUS PAIRS. The members of each pair will be the same length, have similar banding, and will have the centromere in the same location. Use the banding patterns and compare them to the key. Arrange the pairs according to their length, from largest to smallest.

4. TAPE OR GLUE each homologous pair to a human karyotyping form positioning the centromeres on the same lines. Place the pairs in order, with the longest pair at position 1, the shortest pair at position 22, and the sex chromosomes at position 23.

5. CLEAN UP your materials before leaving the lab.6. ANALYZE the karyotype to determine the sex of the individual and

whether or not the individual will have Down syndrome.7. ANSWER THE QUESTIONS in pairs.

Questions: One paper per Group vII 1. What is your karyotype spread letter (lower right corner of your paper).2. Why are karyotypes important tools for geneticists, or those scientists who study

genetics?3. What would you be looking for to verify if your fetus has Down’s syndrome?4. Diagram how a non-disjunction could occur. Refer to pg. 324 of your texts.5. Examine your karyotype.

1. Is the fetus male or female? How do you know?2. How many chromosomes does your karyotype reveal?3. What chromosomal abnormality does the child demonstrate?4. Is your karyotype show a haploid or diploid organism?5. Research what type of abnormality your karyotype reveals. What is the

technical diagnosis (the name) for this disorder? What are some of the difficulties this child will face?

6. If your job (such as a doctor) were to inform the parents of the fetus of their test results, what would you say?

7. Imagine you are a parent about to have this child. What could you do with this information, knowing how the results can impact your life? Do you agree with this type of test? Why or why not?

8. Are you always able to easily distinguish a person with a chromosomal abnormality? Do individuals with disorders show “telltale” signs or can symptoms of their conditions be subtle? Can you determine if an individual is suffering from a genetic disorder and why does this matter?