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

2. 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

3. 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)

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

5. 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

7. 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

8. 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

9. 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

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

11. 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

12. 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

13. 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

14. 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?

15. 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.