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 problems2. 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 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