Chapter 14

Human Chromosomes Karyotype: a picture of the chromosomes from a single cell. Used to determine the sex, or possible genetic disorders of an individual. 44 autosomes 2 sex chromosomes

Determining the sex of a zygote: Always determined by the father. All eggs contain one X chromosome Sperm either contain one X chromosome or one Y chromosome.

Pedigree charts Used to show how a particular trait is passed from one generation to the next in a family

Blood types Controlled by more than one gene A, B, O, AB Rh factor

Genetic disorders Recessive disorders: Most common To be afflicted with a recessive disorder, one must have 2 copies of each recessive allele.

PKU (phenylketonuria) The body cannot break down the amino acid phenylalanine Nutrasweet could be deadly If not detected early, or if a specific diet is not followed, serious brain damage can occur. 1 in 60 Caucasians are carriers of the gene that causes PKU. The gene is found on chromosome 12

Tay-Sachs Cannot break down certain fats. Results in brain damage The gene is found on chromosome 15 Mainly affects people of European Jewish ancestry (1 in 30 are carriers)

Cystic Fibrosis Affects digestive system and absorption of fats. Causes a build up of mucus in the lungs. CF kids are often more likely to develop pneumonia. One of the first disorders to be actively studied for gene therapy.

More CF Sweat test Gene found on chromosome 7 1 in 25 people are carriers. Most lethal autosomal recessive disorder in U.S. No cure

Treatment Respiratory therapy. Enzyme therapy (DNAse) Lung transplants. Boomer Esiason Foundation

Albinism Lack of pigment in skin, hair, and eyes. Approx. 1 in 17,000 people Dangers: 1.Eye problems 2.Severe sensitivity to sunburn.

Autosomal dominant disorders These disorders are expressed when the dominant allele is present in the genotype.

Achondroplasia A form of dwarfism The torso is of normal size, but arms and legs are very short. Average adult height of 4 feet. 1 in 25,000 births. Gene is found on chromosome 4

Huntingtons Results in a loss of muscle control and mental function.  The symptoms usually do not appear until after 30 years old. Approximately 1 in 10,000 births in Europe and N. America Gene on chromosome 4

Sickle cell disease (sickle cell anemia) Codominant disorder found in African Americans. Red blood cells are misshapen. Characterized by extreme pain in legs and arms because the cells get stuck in capillaries. Can be fatal The gene can prevent Malaria

Sickle-cell cont’d Approx 1000 babies born each year 1 in 400 African Americans Possible cure: bone- marrow transplants Treatment: –Avoid being overly active –Watch your diet

Sex-linked genes and disorders A situation in which an organism’s sex can affect the chances of inheriting a gene. First studied by Morgan with fruit flies Most sex-linked genes are found the X chromosome. Why? Much larger.

Color blindness gene Recessive gene located on the X chromosome. Does color blindness affect more men or women? Ans: MEN Men only have one X chromosome, thus only one copy of the color blind gene.

Color Blindness

Hemophilia A disorder in which a person’s blood does not clot properly. Gene found on X chromosome. 1 in 10,000 males born are afflicted.

More hemophilia: Main type: hemophilia a. Body cannot manufacture a specific protein needed for proper blood clotting. Traditionally treatment: periodic blood transfusions Known as the “royal disease” Why?

ALD (adrenoleukodystrophy) Similar to multiple sclerosis. Body is unable to break down long chain fatty acids. Results in destruction of myelin (insulating material around the nerves) Affects only boys. Fatal Depicted in the movie “Lorenzo’s Oil”

Duchenne muscular dystrophy Weakening and loss of muscle tissue. 1 out of 3000 males born in U.S. Genetic disorder website

Chromosomal disorders A disorder resulting from either the loss of or gain of part or a whole chromosome. Nondisjuntcion : most common chromosomal mutation. When a gamete contains either an extra or one less chromosome. Occurs during meiosis.

Nondisjunction diagram:

Down Syndrome Also known as Trisomy 21 because of the presence of an extra chromosome 21. Symptoms similar to mental retardation Approx 1 in 800 babies born in U.S. Chances of having a baby with Down Syndrome increases with the age of the mother.

Sex Chromosome Disorders: Turner’s syndrome: In females, a person only inherits one X chromosome (45,X) Klinefelter’s syndrome: In males, an extra X chromosome is present (47,XXY)

DNA analysis Testing for alleles : makes it possible to determine if a person can pass on a particular disorder to his or her children. DNA fingerprinting

Human Genome Project Began in The goal was to analyze the entire human DNA sequence (6 billion base pairs) Originally scheduled to be completed in 2005 In June 2003, the map was completed

Gene Therapy Replacing an absent or faulty gene with a copy of a “good” or working gene. Still considered a radical therapy. Has not been tested thoroughly.

Assignment: Page –1-10, 12,14,17,19,23,25,26,29