IGCSE Biology Extended 17.1.3—Allele as an alternative form Topic Practice

Red-green colour blindness is a sex-linked characteristic. It is controlled by a gene on the X chromosome.

There are two alternative versions of this gene:
- no colour blindness $\mathbf{X}^{\mathbf{A}}$
- colour blindness $\mathbf{X}^{\mathbf{a}}$.

State the term used to describe an alternative version of a gene.

The flowers of pea plants can be pollinated by bees.

Following fertilisation, seeds will form.

In pea plants there are two alleles for height:
- tall (T)
- dwarf (t)

Define the term allele.

Allele frequency in a population can be changed by natural selection and artificial selection.

State the meaning of the term allele.

Which name is given to different versions of a gene?

What are alleles?