-Sex (gender) DeterminationDr. Thomas Hunt Morgan (1866-1945) -worked with fruit flies (Drosophila melanogaster)-pioneer in the use of fruit flies to study genetics and heredity

Normal Fly

White Eyes

Short Wings

Curly Wings Yellow Body Ebony Body

Fruit Fly (Drosophila melanogaster) Phenotypes

-Early in his work, he viewed karyotypes of fruit fly chromosomes,and noticed that male and female Flies had slightly different chromosomes.

Fruit flies have 4 pairs of chromosomes, so the diploid number is 8.

The Fruit Fly Karyotype

3 of the pairs are homologous, and thesame in male and female. The 4th pair is different in male and female.

The 3 pairs that are the same are called autosomal, and are not involved in gender determination.

Sex-Linked Traits-In 1910, Dr. Morgan found that the trait of white eyes was found mostlyin males (but does happen in females).-He hypothesized that the recessive gene for eye color was on the X chromosome, and that the trait was sex-linked.

He carried out 2 crosses to test hishypothesis.1) Cross a white-eyed male with a red-eyed female. Result: 1/2 red eyed females 1/2 red eyed males

So what will the genotypes of the parents look like?

Xr Y

XR

XR

XRXr

XRXr

XRY

XRY

2) Cross one of the F1 red-eyedfemales with a red-eyed maleResult: 1/2 red-eyed females

1/4 red-eyed males 1/4 white-eyed males

Start with the genotypes of the parents.

XR Y

XR

Xr

XRXR

XRXr

XRY

XrY

He predicted that he could produce awhite-eyed female by crossing an F1red-eye female with a white-eye male.

XRXr x XrY

Xr Y

XR

Xr

XRXr

XrXr

XRY

XrY

Many sex-linked abnormalities arecaused by a recessive gene on the Xchromosome.

Examples:Red-green color blindnessHemophilia

Nondisjunction-failure of chromosomes to segregateduring meiosis, resulting in abnormalchromosome numbers in future generations. -Nondisjunction may happen to anychromosome, autosomal or not.

Nondisjunction in sex chromosomescan result in many genotypes, such as:

XY (not viable)XXX (“super females”)XXYXXXY (not viable)

The following diseases are caused by a

nondisjunction of the

chromosomes.

Down’s Syndrome:-caused by a nondisjunction in the 21st pair of chromosomes.

-symptoms include mental retardation,abnormal facial traits, short arms and legs, many internal defects.

Downes Syndrome

Turner Syndrome:-caused by a nondisjunction of sexchromosomes.-X genotype (therefore female)Symptoms: sterile, usually short, below average intelligence, usually fail to develop normal female characteristics.

Turner Syndrome

Klinefelter’s Syndrome

-Individuals have an XXY genotype, so therefore are male.-Sterile, usually fail to develop normal male sex characteristics. -Very long arms and legs-Below average intelligence

Klinefelter’s Syndrome

Affected individuals rarely live past infancy because of the life-threatening medical problems associated with this condition.

-skeletal abnormalities, including polydactyly and syndactyly

-weak muscle tone (hypotonia)

-a cleft lip-an opening in the roof of the mouth (a cleft palate)These abnormalities include: small eyes

-a chromosomal condition that is associated with severe cognitive disability and certain physical abnormalities.

Trisomy 13 (Patau Syndrome)

Patau Syndrome

Polydactyly

http://upload.wikimedia.org/wikipedia/commons/1/1c/Polydactyly_01_Lhand_AP.jpg

Syndactyly

Most cases of trisomy 13 result when each cell in the body has three copies of chromosome 13 instead of the usual two copies.

A small percentage of cases occur when only some of the body's cells have an extra copy of chromosome13, resulting in a mixed population of cells with a differing number of chromosomes. Such cases are sometimes called mosaic trisomy 13.

Mosaic trisomy 13 results from a non-disjunctionin a somatic cell during early development.

A young boy (7) sufferingfrom Patau Syndrome.

He is deaf, and legally blind.

The following diseases are not caused by a nondisjunction in any chromosomes.

Tay-Sachs Disease-Affects mostly Jewish people.-caused by a homozygous recessivegene. Symptoms: nervous system does Not develop normally, causes inability to move. Death by age 2 or 3.

PKU-caused by a homozygous recessive gene.Symptoms: missing enzyme, can lead to severe mental retardation. this condition can be helped with a special diet. (no phenylalanine)NO!- Diet sodas, nutra-sweet

Huntington’s Disease-due to a dominant gene, thereforea person heterozygous can have the condition. Symptoms: deterioration of the brain,leading to memory loss, and lossof control of movement.

Cystic Fibrosis-caused by a recessive gene on the 7th chromosome pair.Symptoms: lining of lungs does notproduce fluid, causing particles tobe retained in lungs. Chronic cough,difficulty breathing. Death usuallyby 20 years of age.

Sickle-Cell Anemia-This disease affects mostly African Americans. -Homozygous recessive disease.-Causes irregular shaped red blood cells,hemoglobin that does not hold oxygen well. -Clotting due to cell shape, anemia due to low affinity of hemoglobin for oxygen.

In equatorial Africa, where the disease originated, it is actuallybeneficial to have sickle cell, because it protects you from having malaria, which is far more deadly.

Methods of Disease Detection1) Amniocentesis: Fluid that surrounds the fetus is withdrawn with a needle, and analyzed for chromosome abnormalities

Examples: Downs Syndrome,Turner Syndrome Klinefelter Syndrome

2) Ultrasound: High frequency soundwaves “echo” from the fetus, and givea picture.-can be used to see any physical abnormalities.EX: limb development, internal organs

DNA needs to be in the form of chromosomes to be seen clearly.Sex of fetus can also be determined.

3) Fetoscopy:fetus is viewed with a small camera called an endoscope.

The endoscope is inserted through a small incision in the mothers abdomen.

EX: heart septum repairs, digestivetract repairs.

Small samples of tissue or blood maybe taken, some surgical procedures are now performed.