Development of Aneuploids

Phenotypic Effects of Aneuploidy

Genetics of Aneuploidy



Euploidy and Plant Speciation

Variation in Chromosome Number WWW Links

Genetic Topics

Phenotypic Effects of Aneuploidy

The table below is a list of some of the aneuploids of humans. The best known condition is probably Down's Syndrome which results from an extra copy of chromosome 21. An important point to remember is that aneuploidy is usually lethal in animals, but can be tolerated to a greater extent in plants.

Human Aneuploid Conditions

Condition Formula Nomenclature Birth
Down's Syndrome 2n+1 47,+21 1/700 Round, broad head;simian palm crease; narrow, high palatte; low IQ
Edward's Syndrom 2n+1 47,+18 1/7500 Mental retardation; multiple congenital defects of all organs; death within
6 months
Patau Syndrome 2n+1 47,+13 1/15,000 Simalr to Edward;s Syndrome; death within 3 months
Turner's Syndrome 2n-1 45,X 1/2000
Retarded development of feamle >sex organs; sterility
Poor male sex organ development; breast development; subfertility

As was mentioned above the effects of aneuploidy are not as severe in plants. Provided as examples are the following photos and description of wheat nullisomic and tetrasomic stocks. The diploid number of wheat is 21. Extensive analysis strongly suggests that it consists of seven groups (called homoeologous groups) containing three chromosomes each. The proposed development of this species will be discussed later. The data comes from: Dr. E.R. Sears, "The Aneuploids of Common Wheat", University of Missouri Research Bulletin, November 1954.

"Homoeologous Group I. The three nullisomics of this group are reduced in plant height in varying degrees and have spikes that are a little less dense than normal, with slightly stiffer glumes (Fig. 2). All three nullisomics are both female and male fertile. On the basis of vigor and fertility of the nullisomics, chromosome I is the least essential of the three with XIV slightly less essential than XVII. The tetrasomics are all slightly less fertile than the normal, tetra-XIV being the least fertile. The monosomics and trisomics are essentially normal under favorable conditions."

Effects of Nullisomics

  • male and female fertile
  • chromosome 1 less essential for fertility
Effects of Tetrasomics
  • slightly less fertile
Insert Group I Scan Here

"Homoeologous Group 2. This is a very distinctive group. All three nullisomics are very dwarfish, with greatly reduced tillering. All are male fertile but male sterile. The spikes have thin, papery glumes and are completely awnless. The three tetrasomics are virtually indistinguishable from each other. All have small culms and narrow leaves, with increased awn length, and with glumes somewhat stiffer than normal. The trisomics are distinguishable from normal by their rather narrower leaves and longer awns. The monosomics tend to be coarser than normal, with slightly shortened awns and reduced fertility except under very favorable conditions. In this series, deficiency for chromosome II seems to cause the greatest abnormality and XX the least."

Effects of Nullisomics

  • dwarf
  • less tillering
  • female fertile
  • male sterile
  • awnless
  • chromosome II has the greatest effect
Effects of Tetrasomics
  • small culms
  • narrow leaves
  • longer awns
Copyright © 1997. Phillip McClean