Chapter 18, Problem 1VCQ

Figure 18.14 Which is most likely to survive, offspring with 2n+l chromosomes or offspring with 2n-l chromosomes?

Summary Introduction

To analyze:

The survival ability of an offspring with 2n+1 chromosomes or an offspring with 2n-1 chromosomes.

Introduction:

The accuracy of cell division is very important in the production and the survival of the normal offspring. Any error in the cell division can lead to the presence of an abnormal number of chromosomes in a cell. One such condition in which, a cell is missing one chromosome or showing an extra chromosome is called aneuploidy.

Explanation of Solution

Aneuploidy is observed when chromosomes undergo non-disjunction or do not separate properly between the two diving cells at the time of cell division. Two types of aneuploidy are the monosomy and the trisomy. Monosomy refers to lack of one chromosome of the normal chromosomal complement resulting in 2n-1 condition.

Trisomy refers to the presence of three copies of a particular chromosome resulting in 2n+1 condition. Monosomy is said to be harmful as the missing chromosome causes an imbalance in the genome or the genes are lost from the chromosome set. In most of the cases, such embryos with 45 chromosomes instead of 46 will die. Whereas, the presence of trisomy is less lethal as the genetic material is not lost and the embryos remain viable.

Conclusion

Thus, loss of genetic material is always lethal to any organism and therefore, an organism with 2n+1 chromosome is more likely to survive.