In this article we will discuss about:- 1. Meaning of Gynandromorphs 2. Types of Gynandromorphs 3. Origin and Occurrence.
Meaning of Gynandromorphs:
Gynander or gynandromorphs are the organisms in which the body consists of both male and female parts. Such organisms showing both female and male characteristics are called gynanders or gynandromorphs.
The term is derived from the Greek words (gyne = woman; aner = man and morphe = form). Thus, in these animals one part of the body shows female and the other part male features. These occur in silkworms, bees and fruit flies. Gynandromorphs were first described in Drosophila by Morgan and Bridges.
Types of Gynandromorphs:
Depending upon the position of sex tissue, the gynanders may be of the following types:
1. Bilateral Gynanders:
Some times one half of the body shows female characters while other half shows male characters. Sex intermediates of this type are called bilateral gynanders.
2. Anterior-Posterior Gynanders:
In such gynanders anterior region of the animal body has the characteristics of one sex and posterior half region has the characteristics of the other sex.
3. Sex Piebalds:
In these gynandromorphs the body consists of female tissue having spots of male tissue scattered irregularly. There are certain cases in which a few cells of the body show sex difference.
Origin and Occurrence of Gynandromorphs:
The gynandromorphs are supposed to have produced mainly by two or three methods:
(i) By Elimination of X-chromosome:
Generally, gynander begins its development with two X’s. But in later stage of cell division one X gets disappeared or lost in daughter cells. Two X chromosomes in the mitosis become divided in to four X daughters chromosomes.
One daughter cell receives two X’s, and the other daughter cell gets only one X while fourth X becomes lost due to abnormal cell division. The daughter cells receiving two X’s forms the female tissue while the other daughter cell receiving one X develops in to male tissue. The example is Drosophila.
(ii) By Retention (= holding) of Polar Nucleus in the Egg:
In silk worms female is XY. During Meiosis X and Y get separated, either of one X or Y going to egg and polocyte. But some times polar body nucleus remains in the egg along with egg nucleus. Thus, these eggs will be bi-nucleate (XY). As a result of fertilization two sperm cells which contain X, fuse with X and Y chromosome separately giving rise to male (XX) and female (XY) tissues respectively.
In bees also bi-nucleate eggs are found either due to fusion of polar body nucleus with egg nucleus or parthenogenetically producing gynanders. If this bi-nucleate egg was fertilized by single X carrying sperm then, only one of the two nuclei will be fertilized and this one will give rise to female tissue. The unfertilized nucleus will give rise to male tissue.
Another possibility is that normal egg is fertilized by two X carrying sperm cells one of which combines with egg nucleus as usual, but the other one does not. The later then might give rise to haploid tissue, this would be male tissue.
The fertilized nucleus would give rise to female tissue. Muller described another possibility of the gynander formation in a parasitic wasp-Habrobracon. In this wasp, female are heterozygous (XY) and males are either homozygous or haploid (XX).
The egg during oogenesis may come to contain polar nucleus as a result of fusion. Suppose egg nucleus is ‘a’ and polar nucleus is ‘b’, then both ‘a’ and ‘b’ will be inside the egg as it is bi-nucleate egg. If this bi-nucleate egg is fertilized by two sperms (suppose having ‘b’) the fertilized nuclei will be ‘ab’ and ‘bb’. The first ‘ab’ will form female tissue and ‘bb’ will develop in to male tissue.
Thus gynanders are produced mainly by the bi-nucleate eggs which are characteristic of certain bee races. These changes may also be brought about by sex hormones secreted by the primary sex glands. In rigid sense ‘gynandroniorph’ should be confined to individuals in which secondary sexual characters are not under the control of sex hormones.