1. Genetic Screening and Counselling Higher Human Biology Unit 1

2. Use of Family Histories A pattern of human inheritance can be revealed by collecting information about a particular characteristic from the members of a family and then using it to construct a family tree (pedigree) There are 3 types of pedigree that you need to know about

3. Autosomal recessive inheritance The trait is rarely expressed The trait tends to skip generations The trait is expressed in some cousins Males and females are equally affected All sufferers of the trait are homozygous recessive Non-sufferers are homozygous dominant or heterozygous

4. Autosomal recessive inheritance e.g Cystic Fibrosis

5. Autonomic Dominant inheritance The trait appears in every generation Each sufferer has an affected parent When a branch of the family does not express the trait it fails to reappear in future generations of that branch Males and females are equally affected All non-sufferers are homozygous Sufferers are homozygous dominant or heterozygous

6. Autosomal Dominant Inheritance e.g. Huntington’s Chorea

7. Sex-linked recessive More males are affected than females None of the sons of an affected male show the trait Some grandsons of affected males show the trait All sufferers of the trait are homozygous recessive Non-sufferers are homozygous dominantor or heterozygous carrier females

8. Sex-linked recessive trait e.g. haemophilia

9. Pre-natal Screening Two methods of pre-natal screening depend on fetal material being obtained to allow karyotypes to be examined

10. Amniocentesis Amniocentesis is carried out in the 18 th week of pregnancy It slightly increases risk of miscarriage

11. Chorionic Villus Sampling Cells are used for karyotyping CVS can be carried out at 8 weeks of pregnancy Causes a higher risk of miscarriage then amniocentesis

12. Post-natal Screening At present none of the inherited disorders can be successfully treated except for PKU Phenylketonuria results from an inborn error of metabolism If not detected soon after birth the baby suffers from mental retardation All British babies are routinely tested for excess phenylalanine after birth by means of a blood test

13. Testing for PKU