Question 18M.2.HL.TZ1.b.i
| Date | May 2018 | Marks available | [Maximum mark: 1] | Reference code | 18M.2.HL.TZ1.b.i |
| Level | HL | Paper | 2 | Time zone | TZ1 |
| Command term | Distinguish | Question number | b.i | Adapted from | N/A |
The land snail Cepaea nemoralis is very common in North America and in Europe.
The base colour of its shell varies between brown, pink and yellow, and also in its intensity. Some shells are unbanded, but most show one to five bands of different width on top of the shell base colour.
The genes coding for the shell base colour and the presence of banding have linked loci. Allele C causes a dark pink shell and is dominant to allele c, which codes for a dark yellow shell. Allele B codes for the absence of bands and is dominant to allele b, which codes for the presence of bands.
Distinguish between sex-linked genes and genes with linked loci.
[1]
sex-linked genes are on sex/X chromosome(s)/on chromosome 23 whereas genes with linked loci are on the same autosome/chromosome
