Chapter 12Patterns of Heredity and

Human GeneticsSection 1

Mendelian Inheritance of Human Traits

Pedigree

• A pedigree is a graphic representation of genetic inheritance.

• Symbols are used to show the trait being studied and family relationships

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Answer the following about the above pedigree

• a. What is the sex of I 1? ___________________

• b. How many children does IV 2 have? ___________

• c. How many children of IV 12 have cancer? ____________

• d. List all of the males who have polyps (carriers) __________

Dominant Autosomal Heredity

• Follow Rule of Dominance

• Tongue curling

• Free earlobes

• Huntington’s disease

Huntington’s Disease

• Lethal genetic disorder caused by rare autosomal dominant allele

• Nervous system disintegrates causing loss of control of limbs and mental deterioration.

Huntington’s disease

• Since onset occurs between ages 30 and 50, this defect can be transmitted to new generations before the parent knows that he is a carrier.

Huntington’s

• Genetic testing can determine if a person is a carrier.

• Carriers will get disease because allele is dominant.

www.about-dementia.com/huntingtons/hd-causes.php

Recessive Autosomal Heredity

• Genetic disorders caused by recessive alleles.

• Most genetic disorders are caused by this type of allele.

• Cystic fibrosis, sickle -cell anemia, Tay - Sachs disease, Phenylketonuria (PKU).

Cystic Fibrosis• Most common lethal genetic

disorder in white Americans.• Characterized by thick mucus

in lungs and digestive tract.• Food is not digested properly• Breathing is difficult - frequent

lung infections

Tay- Sachs• Absence of enzyme that breaks

down a lipid that is produced and stored in the central nervous system. Lipid builds up in brain membranes

• Common in Eastern European Jews and Pennsylvania Dutch.

Symptoms of Tay-Sachs Disease

• Blindness

• Progressive loss of movement

• Mental deterioration

• Death by age 5.

• See pg 312 for pedigree

Phenylketonuria (PKU)

• Most common in people of Norwegian and Swedish descent.

• Caused by absence of enzyme that converts phenylalanine to tyrosine (amino acids).

Symptoms of PKU

• New born appears normal.

• Once baby starts drinking milk, which is high in phenylalanine, damage occurs

Symptoms

• Build up in phenylalanine causes severe central nervous system damage resulting in mental retardation.

Treatment of PKU• All newborns are tested for

PKU.

• Changes in diet can prevent damage.

New Problems With PKU

• If a homozygous recessive female becomes pregnant, high levels of phenylalanine in her blood can damage baby.