A2 3.4 Unit 4: 3.4.2 Growing up, growing old and passing on your genes

Genetic Counselling and Mendelian inheritance
Candidates should be aware that many conditions needing treatment, or with the potential to need treatment, are inherited.

Cystic fibrosis as an example of monohybrid inheritance. Sickle cell anaemia as an example of codominant alleles. ABO blood groups as an example of inheritance involving multiple alleles. Rhesus blood groups. The potential dangers inherent in a rhesus negative mother giving birth to rhesus positive babies.

Candidates should be able to give reasons why experimental results may only approximate to Mendelian ratios. They should be able to apply the chi-squared test to establish the significance of any differences from predicted ratios. Genetic counselling. The use of information from family history and genetic screening to advise parents, the screening of embryos.

Candidates should consider the ethical and moral issues relating to genetic counselling.

Sex-linked conditions and their inheritance
Sex-linked inheritance. Duchenne Muscular Dystrophy. The reasons why these conditions are rare in women.