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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 - PowerPoint PPT Presentation
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ObjectivesObjectivesIdentify five factors that
influence patterns of heredityDescribe how mutations can
cause genetic disordersList two genetic disorders, and
describe their causes and symptoms
Evaluate the benefits of genetic counseling
Characters Influenced by Characters Influenced by Several GenesSeveral GenesPolygenic 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 CharactersIntermediate CharactersIncomplete Dominance:
individual displays a phenotype that is intermediate between two parents
Intermediate CharactersIntermediate CharactersIncomplete 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 AllelesThree of More AllelesMultiple Alleles: genes with
three or more allelesEx. 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
CodominanceCodominanceCodominance: 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 Characters Influenced by the Environment 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 DisordersGenetic DisordersMutation: changes in genetic
material Genetic Disorders: harmful
effects produced by inherited mutations
Human Genetic Disorders
Disorder 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
Recessive 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
Dominant Deterioration of brain tissue in middle age; shortened life expectancy
Inhibitor of brain-cell metabolism is made
1 in 10,000
Treating Genetic Treating Genetic Disorders Disorders Most cannot be cured
◦Progress being madeGenetic 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 TherapyGene TherapyGene 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
ReviewReview
1. What is the difference between incomplete and codominance?
2. What are examples of some genetic disorders that are recessive?
3. Why would one utilize genetic counseling?
Review- AnswersReview- Answers1. 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.
2. Examples of recessive genetic disorders are: sickle cell anemia, tay-sachs, cystic fibrosis, hemophilia A
3. One may utilize genetic counseling if they believe they or their offspring is at risk for a genetic disorder.