Biology, Eighth Edition (Raven)

Chapter 15: Genes and How They Work

Changes in Chromosome Structure

Why do genes exist in chromosomes? The pairing of homologous chromosomes during prophase I of meiosis can lead to a number of errors. This animation describes how miss-pairings can result in duplication or deletion of entire sections of chromosomes or inversions of sections so that the order of a DNA sequence is reversed with respect to the rest of the chromosome. Given the potential problems associated chromosome pairing in meiosis, why are genes organized onto chromosomes. Why is the DNA for each gene not an independent unit? There are two probable answers to this question. One is that regulatory sites are usually located next to the protein coding genes they control. Regulation that is based on location requires that genes be organized onto larger structures. Also, if each gene was an independent unit during meiosis, the cell would have to pair up thousands and thousands of alleles. Even if cells were capable of doing this the rate of error would be extremely high.

View the animation below, then complete the quiz to test your knowledge of the concept.



1.

Which of the following causes an extra copy of a chromosomal region to occur?
A)inversion
B)duplication
C)deletion
D)simple translocation
E)reciprocal translocation
2.

When a chromosome is broken in two places and reconnected so that a region is flipped from the normal order, this is called...
A)inversion
B)duplication
C)deletion
D)simple translocation
E)reciprocal translocation
3.

Which of the following occurs when a piece of one chromosome breaks off and is attached to another chromosome?
A)inversion
B)duplication
C)deletion
D)simple translocation
E)reciprocal translocation
4.

A chromosomal mutation is a substantial change in the structure of a chromosome or chromosomes.
A)True
B)False
5.

Both inversions and translocations can lead to overall deficiencies and duplications of genetic material.
A)True
B)False
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