Section 4: Complex Patterns of Heredity Chapter 8 Section 4: Complex Patterns of Heredity Grade 10 Biology Spring 2011

Objectives Identify five factors that influence patterns of heredity Describe how mutations can cause genetic disorders List two genetic disorders, and describe their causes and symptoms Evaluate the benefits of genetic counseling

Characters Influenced by Several Genes Polygenic Inheritance: when several genes influence a character May be scattered along the same chromosome or located on different chromosomes Ex. Eye colour, height, weight, hair, skin colour (have degree of intermediate conditions)

Intermediate Characters Incomplete Dominance: individual displays a phenotype that is intermediate between two parents

Intermediate Characters Incomplete Dominance: Ex: snapdragons Red flower x white flower = pink flowers Neither the red or white allele is completely dominant over another Flowers appear pink because they have less red pigment than red flowers

Three of More Alleles Multiple Alleles: genes with three or more alleles Ex. ABO blood groups (blood types) Determined by 3 alleles: IA, IB, i IA and IB are dominant over i, but not over each other Therefore 4 different blood types: A, B, AB, O

Codominance Codominance: two dominant alleles are expressed at the same time, both forms of character are displayed Blood type is an example Different than incomplete dominance because both traits are displayed

Characters Influenced by the Environment An individuals phenotype often depends on conditions in the environment Hydrangea flowers display flowers from blue to pink Acidic soil = blue flowers Neutral to basic soil = pink flowers Ex. Siamese cat, arctic fox, humans

Genetic Disorders Mutation: changes in genetic material Genetic Disorders: harmful effects produced by inherited mutations

Human Genetic Disorders Dominant or Recessive Symptom Defect Frequency Sickle Cell Anemia Recessive Poor blood circulation Abnormal hemoglobin molecule 1 in 500 (African Americans) Hypercholesterolemia Dominant Excessive cholesterol levels in blood, leading to heart disease Abnormal form of cell surface receptor for cholesterol 1 in 500 Tay-Sachs Disease Recessive in early childhood Deterioration of central nervous system; death Defective form of a brain enzyme 1 in 3,500 (Ashkenazi Jews) Cystic Fibrosis Mucus clogs organs (lungs, liver, pancreas) Usually do not survive to old age. Defective chloride-ion transport protein 1 in 2,500 (Caucasians) Hemophilia A (Classical) Sex-linked recessive Failure of blood to clot Defective form of a blood clotting factor 1 in 10,000 males Huntington’s Disease Deterioration of brain tissue in middle age; shortened life expectancy Inhibitor of brain-cell metabolism is made 1 in 10,000

Treating Genetic Disorders Most cannot be cured Progress being made Genetic counseling: form of medical guidance that informs people about genetic problems that could affect them or their offspring Some disorders if caught early enough can be treated PKU in newborns

Gene Therapy Gene Therapy: replacing defective genes with copies of healthy ones First step is to isolate a copy of the gene Next step is to transfer a healthy gene into the body and have it replace the defective gene

Review What is the difference between incomplete and codominance? What are examples of some genetic disorders that are recessive? Why would one utilize genetic counseling?

Review- Answers Incomplete dominance is when an individual displays a phenotype that is intermediate between two parents. Codominance is when two dominant alleles are expressed at the same time, both forms of character are displayed. Examples of recessive genetic disorders are: sickle cell anemia, tay-sachs, cystic fibrosis, hemophilia A One may utilize genetic counseling if they believe they or their offspring is at risk for a genetic disorder.