Rare characteristics

Some inherited characteristics are met only rarely. They are inherited in exactly the same way as the eight on the last page — they are simply far less common.

Syndactyly

Two neighbouring fingers or toes joined by skin for part of their length.

Polydactyly

Six fingers on a hand, or six toes on a foot, instead of five.

Albinism

Very pale skin with white hair and white eyelashes. It returns later in this chapter, where its cause is explained.

Eye colour

Brown or blue. Not rare everywhere, but in Sri Lanka blue eyes are uncommon enough to be noticed.

Figure to be added

Figures 20.13 to 20.16 — photographs of each of these characteristics: two joined fingers and two joined toes, a hand and a foot with six digits, the pale skin and white hair of albinism, and a brown iris beside a blue one.

Rare does not mean wrong

These are variations, inherited by the same machinery as hair colour, and the people who have them are not ill. Later in the chapter you will meet inherited conditions that do affect health; keep the two apart, because being unusual and being harmful are different things.

It is not only people

Transmitting inherited characteristics is common to every living thing. Other animals and plants have them just as humans do.

Assignment 20.1

Choose a few plants in your garden and a few animals you come across.
Identify and record a few unchanging characteristics of those plants and animals that you have observed over a period of time.

From what you collect you will find that features such as the nature of an animal's skin, ears, teeth, feet, feathers, colour pattern and beak — and of a plant's flower colour, pods, seeds, fruit taste and height — are all inherited.