Chapter 12, Problem 10P

Indicate which of the four major classes of rearrangements (deletions, duplications, inversions, and translocations) are most likely to be associated with each of the following phenomena. In each case, explain the effect.

a.	semisterility
b.	lethality
c.	vulnerability to mutation
d.	altered genetic map
e.	haploinsufficiency
f.	neomorphic mutation
g.	hypermorphic mutation
h.	crossover suppression
i.	aneuploidy

Summary Introduction

a.

To determine:

The major chromosomal rearrangement that is associated with semisterility.

Introduction:

The process by which the chromosomes are rearranged is termed as chromosomal rearrangement. The chromosomal rearrangements can alter the sequence of DNA. There are many types of chromosomal rearrangements, such as deletions, inversions, and duplications.

Explanation of Solution

Translocation is also an important type of chromosomal aberration in which the chromosome segment moves to a new location within the genome. The process of translocation leads to semistability. The gametes that produce half viable progenies and half non-viable progenies are called semi-sterile gametes.

For example, Robertsonian translocation involves the breaking of the centromere. The chromosomes break the centromere in this type of translocation. The broken centromere affects genetic material and cause semisterility.

Thus, the major chromosomal reraggegement that is associated with semisterility is translocation.

Summary Introduction

b.

To determine:

The major chromosomal rearrangement that is associated with lethality.

Introduction:

The process by which the wild-type genes are lost and the organism dies is termed as lethality. There are many types of lethality, such as embryonic lethality and age-specific lethality.

Explanation of Solution

Lethality is associated with the deletion. Deletion is a type of chromosomal rearrangement that includes the removal of base pairs. The effects caused by reversions can never be reverted as the base pair that are removed cannot be inserted again. The deletion of important bases leads to lethality.

Thus, the major chromosomal rearrangement that is associated with lethality is deletion.

Summary Introduction

c.

To determine:

The major chromosomal rearrangement that is associated with vulnerability to mutation.

Introduction:

The changes in the sequence of nucleotides are called mutations. The agents that cause mutations are known as mutagens. There are many types of mutations, such as point mutation, silence mutations, and neutral mutations. Mutations can cause many severe diseases like cancer.

Explanation of Solution

The chromosomal rearrangement that is associated with vulnerability to mutation is deletion. This is because the deletion of important bases is the most common source for mutations. The deleted bases lead to different types of mutation. For example, the removal of a single nucleotide causes point mutation.

Thus, deletion is the major chromosomal rearrangement that is associated with vulnerability to mutation.

Summary Introduction

d.

To determine:

The major chromosomal rearrangement that is associated with altered genetic map.

Introduction:

Genetic mapping is an important method that indicates the relative location of genes on the chromosomes. The distance between two genes in a chromosome map is known as the map distance.

Explanation of Solution

The genetic map is associated with three types of chromosomal rearrangements. It is associated with deletion, duplication, and translocation because the map distance is affected by deletions and translocations. These two chromosomal rearrangements decrease the length of map distance. Similarly, the duplication of genes increases the length of a map distance.

Thus, deletion, duplication, and translocation are the major chromosomal rearrangement that is associated with altered genetic map.

Summary Introduction

e.

To determine:

The major chromosomal rearrangement that is associated with haploinsufficiency.

Introduction:

The condition in which the half of the genes produce a normal amount of proteins, while the rest half produces an insufficient amount of proteins is termed as haploinsufficiency. Many disorders are caused by haploinsufficiency.

Explanation of Solution

Copy number variation is the process in which a particular segment of nucleotides is repeated continuously in the genome of an organism. It is the cause of haploinsufficiency. The copy number variations are associated with deletions. The disorder 22q11.2 is a type of syndrome that is caused by deletion mutation and leads to haploinsufficiency.

Thus, deletion is the major chromosomal rearrangement that is associated with haploinsufficiency.

Summary Introduction

f.

To determine:

The major chromosomal rearrangement that is associated with neomorphic mutation.

Introduction:

There are several types of mutation. The neomorphic mutation is also a type of mutation. This type of mutation affects both the expression and functions of genes. The neomorphic mutation is also a cause of many disorders.

Explanation of Solution

The neomorphic mutation is associated with duplication. The chromosomal rearrangement that causes the formation of duplicate genes within the genome is termed as duplication. The neomorphic mutations are caused by duplication.

Thus, duplication is the major chromosomal rearrangement that is associated with neomorphic mutation.

Summary Introduction

g.

To determine:

The major chromosomal rearrangement that is associated with hypermorphic mutation.

Introduction:

The mutation that causes an increase in the level of gene expression is called hypermorphic mutation. It affects the gene expression of a gene. The hypermorphic mutation also affects the activity of proteins produced by a hypermorphic gene.

Explanation of Solution

The hypermorphic gene is associated with duplication because duplication is the chromosomal rearrangement that causes hypermorphic mutation. The presence of duplicated genes is very common in the hypermorphic mutation.

Thus, duplication is the major chromosomal rearrangement that is associated with hypermorphic mutation.

Summary Introduction

h.

To determine:

The major chromosomal rearrangement that is associated with crossover suppression.

Introduction:

Chromosomes are present in the eukaryotic organisms. They are “thread-like” in appearance. A chromosome is made up of two units: DNA and proteins. The genes are located on the chromosomes.

Explanation of Solution

Inversion is a region in the chromosome that is caused by two breaks. These breaks rotate some part of the chromosome to 180° and form a loop-like structure. This is called inversion loop.

The way by which chromosomes can exchange the genetic material is termed as a crossover. The crossover suppression is a condition in which there are no crossovers on the inversion loop.

Thus, inversion is the major chromosomal rearrangement that is associated with crossover suppression.

Summary Introduction

i.

To determine:

The major chromosomal rearrangement that is associated with aneuploidy.

Introduction:

Certain cells show chromosome aberrations. They either lack one or more chromosomes, or they have one or more extra chromosomes. They do not have an exact number of complete chromosomes. The process by which cells lack one or more chromosomes or have one or more extra chromosome is termed as aneuploidy.

Explanation of Solution

Aneuploidy is generally associated with duplication. This is because the presence of extra chromosomes generally causes the aneuploidy. The extra chromosomes are generated as a result of the duplicated gene. The process by which duplicate genes are formed within the genome is termed as duplication.

Thus, duplication is major chromosomal rearrangement that is associated with aneuploidy.