Chapter 11

Complex Inheritance and Human Heredity

11.1 Basic Patterns of Human Inheritance

The inheritance of a trait over several generations can be shown in a pedigree

Pedigrees can help us to track and understand genetic disorders

Genetic Disorders Review:

HH= homozygous dominantHh= heterozygoushh= homozygous recessive

A recessive trait is only expressed if it is homozygous recessive

If an individual is heterozygous for a recessive disorder, they are called a carrier.

Types of Recessive Genetic Disorders:

Cystic Fibrosis Affects the mucus-producing glands,

digestive enzymes, and sweat glands Chloride ions are not absorbed into the

cells of a person with cystic fibrosis but are excreted in sweat

Without sufficient chloride ions in the cells, a thick mucus is secreted

Location of the CF gene on chromosome 7

Breathing Treatment for CF

Albinism

Caused by altered genes, resulting in the absence of pigment in the skin and eyes

White hair Very pale skin Pink iris

Tay-Sachs Disease

Caused by the absence of the enzyme responsible for breaking down fatty acids called gangliosides

Gangliosides accumulate in the brain, inflating brain nerve cells and causing mental deterioration.

Dominant Genetic Disorders

You can be either heterozygous or homozygous dominant to inherit a dominant genetic disorder.

Huntington’s diseaseAffects the nervous system Caused by a genetic defect on

chromosome 4– Section of DNA repeats too many times– As the gene is passed down from one

generation to the next, the number of repeats gets larger

– This means that the symptoms develop at younger and younger ages.

AchondroplasiaGenetic

condition that causes small body size and limbs that are comparatively short

Pedigrees

A diagram that traces the inheritance of a particular trait through several generations

Pedigree Symbols

Normal Female Female that expresses the trait Female carrier (half shaded) Normal male Male that expresses the trait Male who is a carrier for the trait

Pedigree Symbols

Roman Numerals (I, II, III, etc.) = Generation number

Arabic numbers (1,2,3, etc) = individuals in a particular generation

Pedigree

I

II

III