Higher Human Biology

1. Higher Human Biology Unit 2 Physiology & Health KEY AREA 4: Ante- and Postnatal Screening

2. Higher Human Biology We are going to build on the knowledge and skills that you developed during N5 and will learn about the following Physiology & Health key areas : - Key Area 1 – Reproductive Organs Key Area 2 –Hormonal Control of Reproduction Key Area 3 – Biology of Controlling Fertility Key Area 4 – Ante- and Postnatal Screening Key Area 5 – Structure and Function of Arteries, Capillaries and Veins Key Area 6 – Structure and Function of the heart Key Area 7 – Pathology of Cardiovascular Disease (CVD) Key Area 8 – Blood Glucose Levels and Obesity

3. Physiology & Health Learning Intentions KEY AREA 4 – Ante- and Postnatal Screening • Antenatal Screening • Postnatal Screening

4. 4a) Antenatal (before birth) screening - Examples A variety of techniques can be used to monitor the health of the mother, developing foetus and baby. Antenatal (prenatal) screening identifies the risk of a disorder so that further tests and a prenatal diagnosis can be offered Examples of Antenatal Screening are:- Ultrasound imaging (Dating Scan and Anomaly Scan) Biochemical tests Diagnostic tests Use of Karyotype Amniocentesis Chorionic villus sampling

5. 4b) Antenatal (before birth) screening - Ultrasound Ultrasound Imaging When the ultrasound scanner is held against a pregnant women’s abdomen, it picks up high-frequency sounds that have bounced off the foetus. These are converted to an ultrasound image on a computer screen Dating Scan Ultrasound imaging is carried out at 8-14 weeks to produce a Dating Scan, which is used to determine the stage of the pregnancy and to calculate the date when the baby is due to be born. Dating scans are used with biochemical tests for marker chemicals which vary normally during pregnancy. Anomaly Scan Ultrasound imaging is carried out at 18-20 weeks, which detects the presence of any serious physical abnormalities in the foetus e.g. Spina bifida

6. 4c) Antenatal (before birth) screening - Biochemical Blood & Urine Tests Routine blood and urine tests are carried out throughout pregnancy to monitor the concentrations of marker chemicals. Biochemical tests monitor the physiological changes that occur during pregnancy e.g. the concentrations of human chorionic gonadotrophin (HCG), alpha-fetoprotein (AFP) Other routine tests to check the health of the pregnant women include:- Renal Function Tests Liver Function Tests Thyroid Function Tests White Blood Cell Counts Red Blood Cell Counts Protein concentration Glucose concentration Urea concentration Calcium concentration Measuring a chemical at the wrong time could lead to a false positive/false negative result. At certain stages of pregnancy a certain concentration of a marker chemical may be normal, but at another stage it could be atypical- this is why biochemical testing is closely synchronised with information gained from ultrasound scanning.

7. 4d) Antenatal (before birth) screening - Diagnostic Diagnostic Testing A screening test is one that is used to detect signs and symptoms associated with a certain condition or disorder. If the signs are found (i.e. atypical results have been confirmed from screening), the probability that the individual is suffering the condition can be assessed as a degree of risk A diagnostic test is a definitive test that produces results that can be used to establish without a doubt whether or not the foetus is suffering a specific condition or disorder. Diagnostic tests may be offered to a pregnant women if:- Screening tests have shown a potential problem There’s a family history of a genetic disorder She belongs to a high-risk group (e.g. women over age of 35)

8. 4e) Antenatal (before birth) screening - Diagnostic Amniocentesis and Chorionic Villus Sampling can be used to prepare a person’s karyotype which shows their complete chromosome complement arranged as homologous pairs Amniocentesis is carried out between 14-16weeks, and involves withdrawing amniotic fluid containing foetal cells. The cells are cultured, stained and examined under a microscope to create the karyotype and allows for chromosome abnormalities to be detected e.g. an extra chromosome 21 indicates Down’s Syndrome Disadvantage – risk of miscarriage Chorionic villus sampling (CVS) involves taking a tiny sample of placental cells using a fine tube inserted into the mothers reproductive tract. The cells are cultured and used for karyotyping. Benefit of CVS - it can be carried out at 8weeks whereas amniocentesis is 14-16weeks Disadvantage of CVS – causes a higher incidence of miscarriage than amniocentesis In deciding to proceed with these tests, the element of risk will be assessed, as will the decisions the individuals concerned are likely to make if a test is positive.

9. 4f) Genetic Screening and Counselling Pedigree charts (family trees) can be used to analyse patterns of inheritance in genetic screening and counselling Once phenotypes of family members are known, the genotypes can be worked out The construction of a family tree looking at genetic conditions/disorders is carried out by a genetic counsellor, in particular when a couple are concerned about passing the trait to their children X and Y chromosomes are called Sex Chromosomes and all other chromosomes are called Autosomes

10. A geneticist can spot the following patterns in autosomal recessive inheritance:- The trait is expressed relatively rarely The trait may skip generations The trait is expressed in some of the offspring of a consanguineous marriage (cousins) Males and females are affected in approximately equal numbers Genotypes of sufferers are homozygous recessive (ff) Genotypes of non-sufferers are homozygous dominant (FF), or heterozygous (Ff) EXAMPLE: Cystic Fibrosis 4g) Autosomal recessive inheritance

11. 4g) Autosomal recessive inheritance

12. 4g) Autosomal recessive inheritance

13. A geneticist can spot the following patterns in autosomal dominant inheritance:- The trait is expressed in every generation Each sufferer of the trait has an affected parent When a branch of the tree fails to express the trait, the trait fails to reappear in future generations of that branch Males and females are affected in approximately equal numbers Genotypes of non-sufferers are homozygous recessive (hh) Sufferers are homozygous dominant(HH) or heterozygous (Hh) EXAMPLE: Huntington’s disease 4h) Autosomal dominant inheritance

14. 4h) Autosomal dominant inheritance

15. A geneticist can spot the following patterns in autosomal incomplete inheritance:- The fully expressed form occurs relatively rarely The partly expressed form occurs much more frequently Each sufferer of the fully expressed form has two parents who suffer from the partly expressed form Males and females are affected in approximately equal numbers All non-sufferers are homozygous for one incompletely dominant allele (HH) All sufferers of the fully expressed form are homozygous for the other incompletely dominant allele (SS) All sufferers of the partly expressed form are heterozygous for the two alleles (HS) EXAMPLE: Sickle-cell disease 4i) Autosomal incomplete dominance

16. 4i) Autosomal incomplete dominance

17. A geneticist can spot the following patterns in sex-linked recessive inheritance:- Many more males are affected than females (if any) None of the sons of an affected male show the trait Some grandsons of an affected male show the trait All sufferers of the trait are homozygous recessive (male XhY and very rarely the female XhXh) Non-sufferers are homozygous dominant (XHY or XHXH) or heterozygous carrier females (XHXh) EXAMPLE: Haemophilia 4j) Sex-linked recessive traits

18. 4j) Sex-linked recessive traits

19. 4k) Postnatal (after birth) Screening Diagnostic testing for metabolic disorders occurs when the baby is just a few days old In the UK, all new-born babies are screened for PKU (Phenylketonuria) by having their blood tested for the presence of excess phenylalanine. PKU sufferers have incurred a substitution mutation meaning that the enzyme that converts phenylalanine to tyrosine is non-functional (therefore causing excessive phenylalanine levels) PKU sufferers are then put on a restricted diet to prevent mental deficiency and other adverse effects.

20. Physiology & Health Questions KEY AREA 4 – Antenatal and Postnatal Screening • Testing Your Knowledge 1 Page 146 Q’s 1-4 2. Testing Your Knowledge 2 Page 155 Q’s 1-3 3. What You Should Know Page 156 Q’s 1-18 4. Quick Quiz