Biologically there are three sexes: female, male and intersex. The sex of a creature is defined by internal and external bodies, sexual anatomy, chromosomes and hormones. Although most of animals fit into either female or male category, intersex in animal kingdom is more common than you might think. It can be represented in many different ways such as ambiguous genitals or DNA chromosomes that are responsible for determining the gender. This time let’s take a look at the strange nature phenomenon known as bilateral gynandromorphs.
Image Source: Wikimedia Commons
What are bilateral gynandromophs? Gynandromorphs are individuals that have some male and some female characteristics or in other words, they belong to intersex gender. Bilateral gynandromorphs are animals that are half male and half female, divided lengthways. Lepidoptera species that include moths and butterflies have shown a big number of such specimens. For example, in the picture above you can seePolyommatus icarus also known as the Common Blue butterfly that is half male and half female.
Image Source: Wikimedia Commons
This phenomenon is occasionally spotted among other species such as crustaceans, although the likelihood to see a bilateral gynandromorph specimen outside of lepidoptera species is very, very low. If we take a look at lobsters, for example, the chance of meeting a bilateral gynandromorph lobster is 1 in 30 million. The odds are a bit higher if you look at the insect world. Fruit flies sometimes look like they have been split right in the middle and glued together – half brown, half yellow. Sometimes one eye is white while other is red. The genitalia of these specimens can be unique such as two full sets of both male and female genitalia. However, most of the time the genitalia is a mix of tissues that don’t look like either male or female reproductive organs.
Image Source: Wikimedia Commons
The reason why this happens is because of chromosome mutations. Normally sex is determined using the XX/XY system, where females have 2X chromosomes and males have 1X and 1Y chromosome. Occasionally a mutation can happen where one female chromosome is lost during the first mitotic division in a female zygote. In this situation, one of the daughter nucleus has 2X chromosomes (XX), and the other daughter nucleus contains only 1X chromosome (XO). The XX nucleus will create a female body while XO nucleus will create a male body in spite of the lack of Y chromosome. That means that the “splitting” of the body has happened during the first mitotic division, when the sex of both the left and the right side has been determined.
Image Source: Wikimedia Commons
When it comes to why the physical features are so different such as the body or eye color, the reason of this is that the eye and body color genes are found within the X chromosome. If the loss of X chromosome happens after the first mitotic division, the animal will become a mosaic gyandromorph. That means it would have patches or regions that are male and female instead of the sharp bilateral contrast between the male and female body halves. These creatures are also known as chimeras, which are essentially the opposite of identical twins, where one embryo turns into two.
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