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Name____________________________ Per____
Ch. 7 STUDY GUIDE
DUE___________
Chromosomal Alterations
Read and annotate the following article to answer the questions and complete the coloring diagrams on the back.
Permanent changes in chromosomes known as mutations may be passed to the offspring of a mating pair if
they exist in cells that produce sperm or egg cells.
One kind of mutation affects only a single gene, while other types of mutations involve the rearrangement of
several of them. For instance, pieces of chromosomes may be lost or exchanged between nonhomologous
chromosomes. When altered chromosomes are passed to offspring, variation increases.
The diagram (on back of page) displays four different types of alterations that can occur in chromosomes.
Focus on the first two alterations, entitled Deletion and Inversion.
The first chromosomal alteration we will discuss is deletion, which is illustrated in the upper left portion of
the diagram. You should begin by coloring the normal chromosomes with genes A to G using seven distinct colors.
When gene deletion occurs, a portion of the chromosome is lost, usually from the end. In our diagram, the
chromosome that has undergone deletion is missing gene A. The remainder of the chromosome should be colored
with the same colors that were used in the normal chromosome. A deletion sometimes results in the loss of an
important gene, with severe consequences to the organism.
We will now turn to the second chromosomal alteration, called inversion. You should continue to use the same
colors for the genes. We will now show how inversion differs from deletion.
We will start again by looking at the normal chromosome, which contains genes A through G (A to G).
When an inversion takes place, a segment of chromosome turns around 180°. Notice that genes C and D have
inverted, so that the sequence of genes in the altered chromosome is different.
At first glance, it may seem that the chromosome is not affected because the genes are present, but the
position of a gene in a chromosome is very important. For example, a gene may be separated from its nearby
regulatory gene as a result of inversion, so its rate of expression may be altered, or it may cease to be expressed at
all. Scientists believe that chromosomal inversion may be a factor in developing cancer cells.
We will now focus on a third type of alteration called Translocation, in which two chromosomes are involved.
Continue your colored as you read below.
A translocation involves the movement of a chromosomal segment from one chromosome to another. The
two chromosomes involved are nonhomologous, which means that they are chromosomes from different
chromosomal pairs. Begin by coloring genes A through G with the colors you used above, and then color the genes
of the second chromosome, genes H to N, with different colors. ( Note: if you do not have enough different colors,
feel free to use green stripes, green dots, red squiggles, etc. to differentiate the gene colors.) Now take a look at
the point at which translocation has taken place. Genes F and G from the first chromosome have moved to the
second chromosome, and genes M and N have moved from the second chromosome to the first. Chromosomes 1
and 2 are now considerably different than they were originally. Certain translocations have been linked to cancer,
and abnormal gametes can result from this alteration.
The final type of chromosomal alteration that we will consider is Duplication. Focus on the lower right portion of the
diagram. The same colors that you used for the genes labeled before should be used here.
In duplication, a chromosomal segment doubles itself. For instance, here we see the normal chromosome with
genes A to G on the left, but genes D and E appear twice after duplication occurs in the abnormal chromosome.
Duplication occurs when a broken segment of one chromosome attaches to its homologous chromosome.
One effect of the repeating genes may be duplicate proteins in an individual. For example, there are two alpha
chains in hemoglobin molecules in human red blood cells. The two molecules may result from a single gene that
duplicated in an ancient ancestor so that the modern descendent now produces two proteins instead of one.
Therefore, duplication may be a factor in evolution.
Questions:
1. What are mutations?
2. What is a deletion mutation? What could be the result?
3. Explain what an inversion mutation is.
4. What is one abnormality that may result from a chromosomal inversion?
5. What is a translocation mutation?
6. Duplication mutations are thought to possibly be a factor in _____________________, which is when
species change over a long period of time.
Biology Student
EQ: Do I carry deadly genes?
Karyotype
Study Guide
Targeted Skills
analysis
Enduring Understanding
Nucleic acids transfer genetic information from generation to generation.
Broad Brush Knowledge
chromosomal disorders
Concepts Important to Know and Understand
Heredity
Core Objectives
9. Interpret the role of genetics in determining heredity and as it applies
to biotechnology.
BACKGROUND INFORMATION
Problems in the number of chromosomes (called chromosomal abnormalities) can be detected in an
organism. In order to do this, cells from the organism are grown in a laboratory. After the cells have
reproduced a few times, they are treated with a chemical that stops cell division at the metaphase stage.
During metaphase, the chromosomes are at the best length for identification. Each chromosome has two
identical chromatid pairs attached at the centromere. The appearance of each chromosome resembles an Xshape. The cells are treated further, stained, and then placed on a glass slide. The chromosomes are
observed under the microscope where they are counted, checked for abnormalities, and photographed. The
photograph is then enlarged, and the chromosomes are individually cut out. The chromosomes are
identified and arranged in homologous pairs. Homologous chromosomes are identical, or matching,
chromosomes. One chromosome in a homologous chromosome pair comes from the mother, the other
from the father. The arrangement of homologous chromosome pairs is called a karyotype. Humans have
46 chromosomes, 23 pairs. A human karyotype would show 23 pairs of homologous chromosomes, lined
up from largest to smallest.
The most common chromosomal abnormalities are caused when the chromosomes do not separate properly
during meiosis (called nondisjuction). A monosomy is when only one homologous chromosome is present
in the organism and a trisomy is when the organism has three copies of a homologous chromosome. The
following are examples of three of the more common nondisjunction chromosomal abnormalities.
If there is a nondisjunction at chromosome 21, the result could be trisomy 21 (3 #21 chromosomes) also
called Down Syndrome.
If there is a nondisjunction at chromosome 23, the result could be trisomy 23 with XXY also called
Klinefelter’s Syndrome.
If there is a nondisjunction at chromosome 23, the result could be monosomy 23 with XO also called
Turner’s Syndrome.
Define
1. karyotype ___________________________________________________________________________
_____________________________________________________________________________________
2. homologous chromosome ______________________________________________________________
_____________________________________________________________________________________
3. centromere __________________________________________________________________________
_____________________________________________________________________________________
4. chromatid pair _______________________________________________________________________
_____________________________________________________________________________________
5. chromosomal abnormality ______________________________________________________________
_____________________________________________________________________________________
6. nondisjunction _______________________________________________________________________
_____________________________________________________________________________________
7. two types of nondisjunction
a) monosomy ________________________________________________________________________
_____________________________________________________________________________________
b) trisomy __________________________________________________________________________
_____________________________________________________________________________________
8. Define Down Syndrome _______________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
9. Define Klinefelter syndrome ____________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
10. Define Turner syndrome ______________________________________________________________
_____________________________________________________________________________________
_____________________________________________________________________________________
Directions
Use the attached pictures to complete the table below.
Figure
1
2
3
4
5
Number of
Autosomes
Number of
Sex
Chromosomes
Gender
Normal or
Abnormal
Type of
Abnormality
Which
Chromosome
has the
Abnormality?
Figure 1
Figure 2
Figure 3
Figure 4
Figure 5