Chapter 14 Human Chromosomes Karyotype a picture of

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 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. v. 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: bonemarrow 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 1990. • 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 363 -364 – 1 -10, 12, 14, 17, 19, 23, 25, 26, 29