The Discworld Graphic Novels: The Colour of Magic and The Light Fantastic

Many fruit fly traits were inherited in a simple Mendeiian way, but some showed odd patterns of inheritance. When peas were crossed it made no difference which parent carried green or yellow seeds. The results were the same whether the male was green and the female yellow, or vice versa. Some traits in flies gave a different result. For certain genes — such as that controlling the colour of the eye, which may be red or white — it mattered whether the mother or the father had white eyes. When white-eyed fathers were crossed with red-eyed mothers all the offspring had red eyes but when the cross was the other way round (with white-eyed mothers and red-eyed fathers) the result was different. All the sons had white eyes and the daughters red. To Morgan's surprise, the sex of the parent that bore a certain variant had an effect on the appearance of the offspring. Morgan knew that male and female fruit flies differ in light is scanned across her retina her ability to tell the colour of the light changes as it passes from one group of cells to the next ...»