Diseases and karyotypes Definitions Autosomes any chromosome that

Diseases and karyotypes • Definitions • Autosomes- any chromosome that is not a sex chromosome. Not the “X” or “Y” • Sex-linked- genes located on the sex chromosome. Usually on the “X” • Nondisjunction- A chromosome mishap in meiosis

Abnormal numbers of autosomes • Metaphase chromosomes are photographed; • the chromosome pictures are then enlarged and • arranged in pairs by a computer according to length and location of the centromere.

Abnormal numbers of autosomes • This chart of chromosome pairs is called a karyotype, and it is valuable in identifying unusual chromosome numbers in cells.

• A Karyotype is a photograph of the chromosomes of a single cell.

Another view

Normal Female

Normal Male

Colchicine added to cells Cells broken open Picture of chromosomes taken Microscope zooms in Chromosomes cut up and arranged

Chromosomal Disorders Individuals are missing a chromosome or have an extra chromosome

Down syndrome: Trisomy 21 • Down syndrome is the only autosomal trisomy in which affected individuals survive to adulthood. • It occurs in about one in 700 live births.

Down syndrome: Trisomy 21 • Down syndrome is a group of symptoms that results from trisomy of chromosome 21. • Individuals who have Down syndrome have at least some degree of mental retardation. • The incidence of Down syndrome births is higher in older mothers, especially those over 40.

Chromosome 21

Abnormal numbers of sex chromosomes • Many abnormalities in the number of sex chromosomes are known to exist. • An X chromosome may be missing (designated as XO) or there may be an extra one (XXX or XXY). There may also be an extra Y chromosome (XYY).

Klinefelter’s Syndrome

XXY • Poor beard growth • Tend to grow fewer chest hairs • Breast development • Wide hips • Long legs • Narrow shoulders

Karyotype of a male with Klinefelter’s syndrome

• Short (<59”) XO • Webbed neck • Sterile • Low hairline

Karyotype of a female with Turner’s syndrome

Autosomal Genetic Disorders • These are a result of genes on the 22 pairs of chromosomes that are not the sex chromosomes (not X and Y)

Sickle Cell Anemia • Autosomal Recessive • Affects the blood • Symptoms: impaired blood circulation, organ damage • Defect: Abnormal hemoglobin molecules – RBC’s • 1/500 African Americans -If heterozygous will not get malaria

Sickle-cell disease • Abnormally shaped blood cells, slow blood flow, block small vessels, and result in tissue damage and pain. Normal red blood cell Sickle cell

Cystic Fibrosis • Recessive allele • Affects the lungs and digestive tract • Characterized by thick mucus in lungs and digestive tract • Food is not digested properly • Breathing is difficult - frequent lung infections

• . Most common lethal genetic disorder in white Americans. • Approximately one in 28 white Americans carries the recessive allele, and one in 2500 children born to white Americans inherits the disorder.

Cystic Fibrosis On chromosome 7 there is a mutation in a gene that causes a thick mucus to develop This is a frame shift mutation

• Autosomal dominant—carriers GET the disease • Affects the central nervous system • Causes nerve death in the brain. Starts with spasms and eventually leads to a vegetable like state and death. Onset between 30 and 50.

Huntington’s Disease Huntington disease affects an estimated 3 to 7 per 100, 000 people of European ancestry. The disorder appears to be less common in some other populations, including people of Japanese, Chinese, and African descent. Defect on Chromosomes number 4

Typical Pedigree of Huntington’s Disease I 1 2 II 2 1 4 3 5 III 1 2 3 4 5

Phenylketonuria (PKU) • Autosomal recessive • Affects: brain • Symptoms: Failure of brain to develop in infancy; if untreated causes death. • Defect: Caused by absence of enzyme that converts phenylalanine to tyrosine (amino acids) • 1/18, 000 urine test, treated by diet until puberty.

Phenylketonuria (PKU) • Most common in people of Norwegian and Swedish descent.

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. Given a diet low in phenylalanine until the brain is fully developed.

Phenylketonuria Phenylketonurics: Contains Phenylalanine

Tay-Sachs disease • Tay-Sachs (tay saks) disease is a recessive disorder of the central nervous system. • In this disorder, a recessive allele results in the absence of an enzyme that normally breaks down a lipid produced and stored in tissues of the central nervous system. • Because this lipid fails to break down properly, it accumulates in the cells.

Symptoms of Tay-Sachs Disease • Blindness • Progressive loss of movement • Mental deterioration • Death by age 5.

I 1 2 Typical Pedigree for Tay-Sachs II 1 2 3 4 1 2 III 3 IV 1

Sex-linked traits • These are genes that are found on the X chromosome. They are generally more common in males than in females. • Females need to have it on both their X chromosomes ( get from mom and dad) • Since males only have 1 X chromosome, they only need to have received the allele from their mother for the trait to show.

Sex-linked trait

Hemophilia • X-linked recessive • Defect: defective form of blood-clotting agent. • Symptoms: failure of blood to clot • About one male in every 10 000 has hemophilia, but only about one in 100 million females inherits the same disorder.

Hemophilia: An X-linked disorder • Males inherit the allele for hemophilia on the X chromosome from their carrier mothers. One recessive allele for hemophilia will cause the disorder in males. • Females would need two recessive alleles to inherit hemophilia.

• Some genetic disorders are both genetic and environmental. People inherit the tendency to a trait, but how and when it is expressed depends on environmental factors such as diet, exercise, exposure to chemicals, etc.

Diabetes Asthma Cardiovascular Disease