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Genetic Screening and Counselling

Genetic Screening and Counselling. Higher Human Biology Unit 1. 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)

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Genetic Screening and Counselling

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  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 inheritancee.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 Inheritancee.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 traite.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 18th 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

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