Question 20N.2.HL.TZ0.a
| Date | November 2020 | Marks available | [Maximum mark: 1] | Reference code | 20N.2.HL.TZ0.a |
| Level | HL | Paper | 2 | Time zone | TZ0 |
| Command term | Identify | Question number | a | Adapted from | N/A |
Dachshunds have three basic coat types: wire-, smooth- or long-haired. These are affected by two genes, W and K. The presence of W always results in wire hair.
[Source: American Kennel Club, 2007. Available at:
https://www.slideshare.net/ghinck/dachshund-power-point.]
When long-haired dogs are crossed among themselves, they always produce long-haired puppies. When dogs heterozygous for both genes are crossed, they produce offspring in the ratio 12 wire-haired:3 smooth-haired:1 long-haired.
A male wire-haired dog was crossed with several long-haired females and the phenotypic ratio of the puppies was approximately 2 wire-haired:1 smooth-haired:1 long-haired.
Identify the genotype of the male wire-haired dog.
[1]
WwKk
Only 40 % of candidates answered this correctly. A surprisingly high number of candidates gave a genotype with only one allele for each gene, suggesting that they were not familiar with dihybrid crosses. In many cases it was hard to distinguish between upper and lower case letters -W/w and K/k. Candidates should be encouraged to make letters used for alleles as clear as possible.
