Karyotypes and Pedigrees Inheritance of Genetic Traits

Karyotypes §Biologists photograph cells in mitosis, when the chromosomes are fully condensed and easy to see (usually in metaphase). §The chromosomes are then arranged in homologous pairs.

Karyotypes §The homologous pairs are then placed in order of descending size. The sex chromosomes are placed at the end. §A picture of chromosomes arranged in this way is known as a karyotype.

Labeling a Karyotype §To label a karyotype correctly, first list the number of chromosomes found in the karyotype. Ex. 46 §Secondly, list the type of sex chromosomes found in the karyotype. Ex. XX §Lastly, list the any abnormalities at the appropriate chromosome number. Normal Human Female: 46, XX Normal Human Male: 46, XY

What are abnormalities? §Sometimes, during meiosis, things go wrong. §The most common error is nondisjunction, which means “not coming apart”. §If nondisjunction occurs, abnormal numbers of chromosomes may find their way into gametes, and a disorder of chromosome numbers may result.

Autosomal Chromosome Disorders §Two copies of an autosomal chromosome fail to separate during meiosis, an individual may be born with THREE copies of a chromosome. §This is known as a “Trisomy” §Trisomy 13, Trisomy 18, Trisomy 21.

Down Syndrome §Most common, Trisomy 21 (down syndrome) §1 in 800 babies born in U.S. with Trisomy 21. §Mild to severe mental retardation §Increased susceptibility to many diseases and a higher frequency of other birth defects.

Down’s Syndrome or Trisomy 21

Kleinfelter’s syndrome XXY §Males with some development of breast tissue normally seen in females. §Little body hair is present, and such person are typically tall, have small testes. § Infertility results from absent sperm.

Turner’s Syndrome One X Female inherits only one X chromosome §Turner syndrome is associated with underdeveloped ovaries, short stature, webbed, and is only in women. §Bull neck, and broad chest. Individuals are sterile, and lack expected secondary sexual characteristics.

Turner’s Syndrome

Pedigrees §A type of “family tree” l Circle – female l Square – male l Shaded – has the trait l Unshaded – does not have the trait l ½ shaded – is a carrier of the trait l Horizontal line – represents marriage l Vertical line – connects parents to children

Male-DAD Female-MOM Carrier Female-daughter Male- Son Oldest to youngest Marriage Has the trait

Pedigrees Example of Sex linked. Notice only females are carriers and only males have the trait:

Pedigree Charts - Autosomes Autosomal Dominant – Trait appears in every generation Autosomal Recessive – Trait appears when two parents by chance carry the hidden allele.

More Genetic Disorders

Sickle Cell Anemia §An inherited, chronic disease in which the red blood cells, normally disc-shaped, become crescent shaped. As a result, they function abnormally and cause small blood clots within your veins §Most commonly found in African Americans (can be linked to the incidence of malaria).

Cystic Fibrosis §Body produces abnormally thick mucus in the lungs and intestines §The thick mucus fills the lungs making it hard to breathe §Common among Caucasians…1 in 20 are carriers §Most die from disease in Early 30’s

Tay-Sachs disease §Monogenic, autosomal recessive §Central nervous system degrades, ultimately causing death. §Most common among people of Jewish, eastern Europe descent.

§Musclular Dystrophy l Sex-linked, defective gene for muscle protein. l Progressive weakening and loss of skeletal muscle. Body get weaker and weaker and slowly stops working. l In U.S., 1 out of every 3000 males born has condition. Other Genetic Disorders

Hemophilia  A person’s blood clots very slowly or not at all  Do not produce one of the proteins needed for normal blood clotting  Small bumps and bruises may cause internal bleeding that can’t be controlled  One can bleed to death with only a small cut or bruise  Sex-linked disorder – occurs more frequently in males

X-linked Inheritance pedigree chart

Huntington’s Disease §Huntington's disease (HD) is an inherited, degenerative brain disorder which results in an eventual loss of both mental and physical control. Patients have "dance- like movements" which refers to the uncontrolled motions often associated with the disease.

Phenylketonuria or PKU People with PKU cannot consume any product that contains aspartame. PKU is a metabolic disorder that results when the PKU gene is inherited from both parents §A low protein diet must be followed. §Brain damage can result if the diet is not followed causing mental retardation…and mousy body odor (phenylacetic acid is in sweat).

§The disease strikes people between the ages of 40 and 70, and as many as 30,000 Americans have the disease at any given time §This mutation is believed to make a defective protein that is toxic to motor nerve cells. §A common first symptom is a painless weakness in a hand, foot, arm or leg, other early symptoms include speech swallowing or walking difficulty ALS

Color Blindness §Cause: x-linked recessive §1/10 males have, 1/100 females have. Why the difference? §Individuals are unable to distinguish shades of red-green. §Are you color blind?

Albinism §Patients are unable to produce skin or eye pigments, and thus are light-sensitive §Autosomal recessive

The very tragic disease… hairy ears Y-linked trait, which are rare §symptoms…hairy ears §Only 1 cure known….