Name:____________________________________________ Period: ____________

 

Chromosomal Mutations of Insects by

Karyotype Analysis

 

Introduction: A chromosome mutation changes the number or structure of a chromosome. Changes in number include monosomy (containing only one copy of a particular chromosome) and trisomy (containing three copies of a chromosome). Normally, individuals contain two copies of each chromosome. Two examples of structural changes are deletions (loss of part of a chromosome containing several genes) and duplications (when part of a chromosome containing several genes is repeated). Chromosomal mutations can be identified through a karyotype. A karyotype is a chart displaying the homologous chromosome pairs in an individualís cells. The chromosomes are stained and then photographed through a microscope during metaphase of the cell cycle. The stain shows the banding patterns on the chromosomes. The photograph is enlarged. Then the chromosome are cut from the photograph and arranged in homologous pairs according to size, centromere position, and banding pattern. Once the chart is organized, the chromosome pairs can be analyzed for defects. Large defects such as changes in chromosome number are obvious. Smaller defects such as duplications or deletions are more difficult to observe.

Procedure:

  1. Look at Figure 1. This figure shows the normal karyotype for a male and female insect. Each banded X represents a chromosome. (They are actually doubled chromosomes, but we will still count them as one chromosome.) The chromosomes are arranged in their homologous pairs. Answer questions 1-3.

 

Text Box: 1.
Text Box: 3.
Text Box: 2.

 
 

Procedure (conít):

 

  1. Cut out the chromosomes for insect #1 ONLY!!!!
  2. Arrange the chromosomes in pairs next to Insect #1 in the section labeled DATA. The chromosome pairs should be placed in the same order as the normal karyotypes in Figure 1.
  3. Glue or tape the chromosomes into place. The centromere (the bead at the center) should be directly on the line provided.
  4. Compare the karyotype of insect #1 you just made with the normal karyotypes. Determine the sex of the insect, the chromosomal error (refer to the chromosome mutation/ genetic disorder table) and the genetic disorder and record in the table in the analysis section. HINT: Two of the insects are normal and have no genetic disorder.
  5. Repeat steps 2-5 for all of the other insects.
  6. Answer questions 4-9.

 

Analysis:

Insect #

Sex (Male or Female)

Chromosomal Mutation (List the type of mutation that occurred and the chromosome # affected) see column one from the Chromosome Mutations and Genetic Disorders Data Table

Genetic Disorder (Write the name of the genetic disorder)

see column two from the Chromosome Mutations and Genetic Disorders Data Table

1

 

 

 

 

 

2

 

 

 

 

 

3

 

 

 

 

 

4

 

 

 

 

 

5

 

 

 

 

 

6

 

 

 

 

 

Questions:

  1. Look at Figure 1. How many chromosomes are present in a normal male and a normal female insect?

 

 

  1. Look at Figure 1. How many chromosome pairs are present in a normal male and a normal female insect?

 

 

  1. Look at Figure 1. Look at the third pair of chromosomes in the male and female insect. These are the sex chromosomes. What is different about the sex chromosomes in the male and female insect?

 

 

 

  1. Which type(s) of chromosomal mutation is the most difficult to detect by means of a karyotype? Explain why.

 

 

 

  1. Which type(s) of chromosomal mutation is the easiest to detect by means of a karyotype? Explain why.

 

 

 

  1. Which two types of chromosomal mutations change the number of chromosomes in the insect?

 

 

  1. Which chromosomal mutation causes monosomy or trisomy to occur? Explain what happens to cause this mutation.

 

 

 

 

  1. On which chromosome number is the gene that determines insect size? How do you know?

 

 

 

  1. What information would you need if karyotype analysis were to be used to detect the genetic disorders of real organisms?

 

 

 

 

 

 

Chromosome Mutations and Genetic Disorders

Chromosome mutation

Genetic Disorder

Picture of Insect

Monosomy of chromosome #3

Size Reduction disorder

Insect is smaller than normal

 

Duplication of part of chromosome #1

Clear Wing disorder

Wings have no coloring and insects are sterile.

Trisomy of chromosome #2

Double disorder

Insect has a double head, bands on wings and extra body segments.

 

Deletion of part of chromosome #3

Unsegmented disorder

Reduction in size, loss of body segments.

 

 

DATA:

 

Insect #1         ____________________________________________________________

 

 

 

 

 

 

 

Insect #2         ____________________________________________________________

 

 

 

 

 

 

 

Insect #3         ____________________________________________________________

 

 

 

 

 

 

 

Insect #4         ____________________________________________________________

 

 

 

 

 

 

 

Insect #5         ____________________________________________________________

 

 

 

 

 

 

 

Insect #6         ____________________________________________________________