Chapter 8

Chapter 8Chapter 8Section 4: Complex Patterns of Heredity

Grade 10 BiologySpring 2011

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.