Case cracker 8 ��������������������������������������������������������

9 Suggest why it might be important for a breeder to know if an animal is homozygous or heterozygous for a particular trait.

10 Suggest why some aspiring parents might request genetic tests before the woman becomes pregnant.

CASE CRACKER 8

KEY SCIENCE SKILL – ANALYSE AND EVALUATE DATA AND INVESTIGATION METHODS

Haemophilia in the royal family

One of the most commonly used case studies for demonstrating inheritance is that of European royalty, particularly the descendants of Queen Victoria. Queen Victoria ruled the United Kingdom from 1837 until 1901. Her descendants went on to marry into royal families from Prussia, Denmark, Norway, Russia, Romania and Spain, taking their genetic inheritance with them.

Queen Victoria was a carrier of the X-linked recessive condition haemophilia, which occurred as a result of a random mutation in either the F8 or the F9 gene on the X chromosome. Haemophilia is a condition in which the blood does not clot properly, and it can cause excessive bleeding internally and externally after even a simple injury. Because there is no record of haemophilia in the royal family before Victoria, it is believed the condition began with her, a possibility made more likely by the fact her father was over the age of 50 when she was conceived (older fathers are more likely to have offspring with haemophilia). 1 Explain why the inheritance of haemophilia in these royal families is a useful case study.

2 A family with a history of a genetic condition will often consider whether they want to have children of their own and risk passing on the condition. Describe the options that are currently available to people who are carriers of the haemophilia allele.