Phenotypic Effects of Aneuploidy
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 Frequency |
Phenotype |
|---|---|---|---|---|
| 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 females |
Retarded development of feamle >sex organs; sterility |
| Klinefelter's Syndrome |
2n+1 2n+2 2n+2 2n+3 2n+4 |
47,XXY 48,XXXY 48,XXYY ,49,XXXXY 50,XXXXXY |
1/500 Males |
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
- slightly less fertile
"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
- small culms
- narrow leaves
- longer awns