1. Chapter 14: Genetic Screening and Counselling. Higher Human Biology Unit 1: Cell Function and Inheritance 07/09/20151Mrs Smith: Ch14: Genetic Screening and Councilling

2. Learning Intentions By the end of this lesson you should be able to- – describe Genetic screening and counselling. –Explain the use of family histories in determining genotypes. Examples might include albinism, Huntington’s chorea, cystic fibrosis, phenylketonuria, haemophilia and muscular dystrophy. –Explain the use of karyotypes of foetal material where there is a possibility of genetic disorder. –Discuss risk evaluation in cases of polygenic inheritance. –Understand post-natal screening for conditions which have a genetic basis. 07/09/20152Mrs Smith: Ch13: Mutations an Chromosomal Abnormalities

3. You need to know these words 07/09/2015Mrs Smith: Ch13: Mutations an Chromosomal Abnormalities 3

4. 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) 07/09/20154Mrs Smith: Ch14: Genetic Screening and Councilling

5. Types of pedigree There are 3 types of pedigree that you need to know about –Autosomal recessive inheritance –Autosomal dominant inheritance –Sex-linked recessive trait. 07/09/2015Mrs Smith: Ch14: Genetic Screening and Councilling 5

6. The Geneticist recognises Autosomal Recessive Inheritance because.... 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. 07/09/20156Mrs Smith: Ch14: Genetic Screening and Councilling

7. Autosomal recessive inheritance e.g Cystic Fibrosis 07/09/20157Mrs Smith: Ch14: Genetic Screening and Councilling

8. The Geneticist recognises Autosomal Dominant Inheritance because.... 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. 07/09/20158Mrs Smith: Ch14: Genetic Screening and Councilling

9. Autosomal Dominant Inheritance e.g. Huntington’s Chorea 07/09/20159Mrs Smith: Ch14: Genetic Screening and Councilling

10. The Geneticist recognises Sex- linked recessive because..... 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 07/09/201510Mrs Smith: Ch14: Genetic Screening and Councilling

11. 07/09/2015Mrs Smith: Ch14: Genetic Screening and Councilling 11 Sex-linked recessive trait e.g. haemophilia

12. 07/09/201512Mrs Smith: Ch14: Genetic Screening and Councilling

13. FYI - Genetic code In 1966, the Genetic code was discovered Human Genome Project to determine nucleotide sequence of human DNA began in 1990 and was completed in 2003. Scientists are now able to predict characteristics by studying DNA. This leads to genetic engineering, genetic counseling. 07/09/201513Mrs Smith: Ch14: Genetic Screening and Councilling

14. Genetic code An international team of scientists began the project to map the human genome. 07/09/201514Mrs Smith: Ch14: Genetic Screening and Councilling

15. Genetic Code 07/09/201515Mrs Smith: Ch14: Genetic Screening and Councilling

16. Genetic Code In 1990, gene therapy was used on patients for the first time 07/09/201516Mrs Smith: Ch14: Genetic Screening and Councilling

17. Assessing the risk! Once the genetic councillor has constructed the family tree(s) and established as many genotypes as possible, he/she is in a position to assess the risk and state the possibilities. 07/09/2015Mrs Smith: Ch14: Genetic Screening and Councilling 17

18. Assessing the risk – Autosomal recessive. e.g. cystic fibrosis If a couple were considering having a family, however the female knows cystic fibrosis runs in her family but not in her partners. They could approach a genetic councillor. By analysing her family tree the councillor could work out there was a 2:3 chance that the female is a carrier. The councillor would already know the frequency in the British population as 1:25 for carrying the heterozygous allele for CF – this is the risk of her partner being a carrier. The councillor would then conclude the risk of having a child with CF as low. Mrs Smith: Ch14: Genetic Screening and Councilling 18

19. Assessing the risk – Autosomal Dominant. e.g. Huntington’s chorea Consider a brother and sister, unlike their siblings they are too young to know if they have received the harmful allele from an affected parent. They could approach a genetic councillor. The councillor would already know the frequency in the British population, and there is a 1:2 chance that each is heterozygous allele for HC By analysing her family tree the councillor would then conclude the risk of having of each sibling suffering this debilitating disease as high. Mrs Smith: Ch14: Genetic Screening and Councilling 19

20. Assessing the risk – sex-linked. e.g. Haemophilia If a couple were considering having a family, however the female knows Haemophilia runs in her family but not in her partners. She is anxious to know if she could pass the trait onto her sons. They could approach a genetic councillor. By analysing her family tree the councillor would note that the woman's brother and sisters son her nephew have developed this sex linked trait. This shows her sister and mother are carriers. The councillor would then conclude a she has a 1:2 risk of being carrier and a 1:4 risk that each son will be a haemophiliac. Mrs Smith: Ch14: Genetic Screening and Councilling 20

21. Advantage and disadvantagr of Genetic counselling The aim of genetic counselling is to help people to make well informed decisions for themselves based on information available. Advantage: Analysis of a family tree allows the expert to chart he pattern of the disorder. Disadvantage: It is of limited value in that it can only offer an assessment of risk. 07/09/2015Mrs Smith: Ch14: Genetic Screening and Councilling 21

22. Pre-natal Screening If after assessing the risk of having baby with a genetic disorder. AND IF the couple decide to go ahead and have a baby pre- natal screening can be employed. Two methods of pre-natal screening depend on foetal material being obtained to allow karyotypes to be examined –Amniocentesis –Chorionic villus sampling (CVS) 07/09/201522Mrs Smith: Ch14: Genetic Screening and Councilling

23. Amniocentesis Amniocentesis is carried out in the 18 th week of pregnancy. It involves the withdrawal of a little amniotic fluid containing foetal cells. These cells can be analysed and a full karotype made. It slightly increases risk of miscarriage 07/09/201523

24. Chorionic Villus Sampling A small tube is inserted into the womans reproductive tract, placental cells are removed, these cells are used for karyotyping ADV: CVS can be carried out at 8 weeks of pregnancy DISADV: Causes a higher risk of miscarriage then amniocentesis 07/09/201524

25. 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 for 1:10000 b irths in Britain. 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 07/09/201525Mrs Smith: Ch14: Genetic Screening and Councilling

26. Testing for PKU: Guthrie's test 07/09/201526Mrs Smith: Ch14: Genetic Screening and Councilling

27. Task: TYK -Torrance pg106 Qu’s 1-3 07/09/201527Mrs Smith: Ch13: Mutations an Chromosomal Abnormalities

28. Task: AYK -Torrance pg 106-7 Qu’s 1-4 07/09/201528 Mrs Smith: Ch13: Mutations an Chromosomal Abnormalities

29. Essay Question Guide to H-Grade essays pg 64 By means o examples you have studied discuss genetic conditions of medical importance with reference to the following: – Family History – Use of Karyotypes –Post-natal Screening. (15) 07/09/2015Mrs Smith29