Name:
Pd. Date
Introduction:
Chromosomes are compact spools of DNA. If you were to stretch out all the DNA from one of your cells, it would be over 1 meter long from end to end! You can think of chromosomes as "DNA packages" that enable all of this DNA to fit in the nucleus of each cell. Normally, we have 46 of these “packages” in each cell; we received 23 from our mother and 23 from our father. A karyotype is an organized picture of a person's chromosomes. We can learn a lot by looking at chromosomes! They can tell us everything from the likelihood that an unborn baby will have a genetic disorder to whether a person will be male or female. Scientists often analyze chromosomes in prenatal testing and in diagnosing specific diseases. Fetal cells from an unborn child are contained in the amniotic fluid (fluid surrounding the baby) and can be tested for hereditary disorders. In a karyotype, chromosomes are arranged and numbered by size, from largest to smallest. This arrangement helps scientists quickly identify chromosomal alterations that may result in a genetic disorder. Scientists can also look at the banding patterns on chromosomes (regions that are lighter or darker) to compare chromosomes to one another. The darker regions of chromosomes are the areas where the DNA is more tightly wound and not often read.
To make a karyotype, scientists take a picture of someone's chromosomes, cut them out and match them up using size, banding pattern and centromere position as guides. Homologous pairs are arranged by size in descending order (largest to smallest) with the sex chromosomes (XX for female or XY for male) as the last or 23rd pair. See below:
Homologous chromosomes have genes for the same trait at the same location.
Since humans have 46 chromosomes in their somatic (body cells), they have 23 pairs of chromosomes in their karyotype. If chromosomes fail to separate in meiosis (sex cell production), a condition called nondisjunction, a person may have more or less than the normal 46 chromosomes on their karyotype. Having more or less information in cells can lead to genetic disorders.
Materials: 1 chromosome sheet, stick glue, scissors, envelope (if you do not complete in class)
Procedure:
q Examine the karyotype chart provide. 1/2 of the homologous pairs have been organized for you.
q Cut out the scrambled chromosomes and try to match them up with their homologous pairs. Paste the matching chromosome next to its homologue.
q Remember that homologous pairs should be the same size and shape. In addition, centromeres and banding patterns (genes loci) should line up.
Analysis:
1. How can a karyotype be useful to a couple wanting to have children?
- What 3 things can you determine by looking at a persons karyotype?
Question: / Answer:
How many pairs of chromosomes are in your karyotype?
How many total chromosomes are in this karyotype?
How many types of chromosomes were unpaired in the karyotype?
How many autosomes does this karyotype show?
How many sex chromosomes does this karyotype show?
Are the sex chromosomes XY or XX?
What is the sex of this individual?
What is the diploid number (2n) of chromosomes for a human body cell?
What is the haploid number (n) of chromosomes for a human body cell?
Is your karyotype of a human body cell or a sex cell?
Help!! à If you are having trouble matching up your homologous pairs go to the following website for assistance:
http://learn.genetics.utah.edu/content/begin/traits/karyotype/