1 Infer How do genetic disorders such as CF support the theory of evolution

2 Review Explain two sex chromosome disorders3 Description Write a paragraph explaining the

process of nondisjunction

CH 14 HUMAN HEREDITY14.2 Human Genetic Disorders

Changes in DNA sequence can change proteins by altering the amino acid sequences, which may affect the phenotype.

African and European ancestry are more likely to have wet earwax (dominant form)

Asian or Native American ancestry most often have the dry form (recessive)

Single DNA base change from guanine (G) to adenine (A) in the gene for a membrane-transport protein causes this change.

Disorders Caused by Individual Genes

Lots of genetic disorders are caused by changes in individual genes.

Sickle Cell Disease

Caused by a defective allele for beta-globin (protein in hemoglobin)

Makes hemoglobin less soluble Causes hemoglobin molecules to stick together

with low blood oxygen level Molecules clump into long fibers.

Sickle Cell Disease

Sickle-shaped cells are more rigid than normal red blood cells

Get stuck in the capillaries Blood stops moving through the capillaries,

damaging cells, tissues, and organs.

Cystic Fibrosis

Results from deleting three bases in the gene for a protein CFTR (cystic fibrosis transmembrane conductance regulator).

CFTR normally allows chloride ions (Cl−) to pass across cell membranes

Deletion causes protein to fold improperly Misfolded protein is then destroyed.

Cell membranes unable to transport Cl−

Tissues malfunction Children have serious digestive problems and

produce thick, heavy lung mucus.

One normal copy of the CF allele are unaffected by CF

Two copies of the defective allele are needed to produce the disorder.

Huntington’s Disease

Caused by a dominant allele for a protein found in brain cells

Allele for this disease contains a long string of CAGs (glutamine) repeats over 40 times more repeats the more severe

Mental deterioration and uncontrollable movements usually do not appear until middle age.

Genetic Advantages

In the United States CF allele is found 1 person in 12 of African ancestry 1 person in 25 of European ancestry

Why that common if it can be fatal if you have 2 copies.

Most African Americans today are descended from west central Africa, where malaria is common

Malaria is a mosquito-borne infection caused by a parasite that lives inside red blood cells.

1 sickle cell gene- still heathly

AND are highly resistant to the malaria parasite.

Similar relationship between CF and Typhoid.

Chromosomal Disorders

Nondisjunction

Homologous chromosomes fail to separate

Results in gametes with an abnormal number of chromosomes.

Most common form of trisomy (3 copies of a chromosome) is Down syndrome (trisomy 21).

Nondisjunction of the X Chromosomes

Turner Syndrome 45, X Karyotype Usually short, underdeveloped, and sterile

Klinefelter Syndrome 47, XXY karyotype.

Geography of Malaria

Malaria is apotentially fatal disease transmitted by mosquitoes. Its cause is a parasite that lives inside red blood cells. The upper map shows the parts of the world where malaria is common. The lower map shows regions where people have the sickle cell allele.

The map is on the following slide

1. Analyze Data What is the relationship between where malaria and the sickle cell allele are found

2. Infer In 1805, a European expedition tried to find the source of the Niger River in Africa. During the expedition most of them died of malaria. Why do you think their native African guides survived

3. Form a Hypothesis Propose an explanation why the sickle cell allele is not found in populations of southern Africa.