-Sex chromosomes determine gender XX: femaleXY: male -In humans the X chromosome is much larger than the Y chromosome and contains thousands of more genes  Very little homologous DNA -X chromosomes are responsible for many non-sexual traits

-Recessive allele carried on the X chromosome but not on the Y chromosome -More common in males... WHY? Males- one X chromosome One copy of a recessive allele results in expression of the trait Females- two X chromosomes Heterozygote: recessive allele is hidden so no expression of the trait  BUT… she is a carrier Homozygote recessive: trait is expressed Examples: Colour blindness and Hemophilia

-Inability to distinguish between certain colours -Absence of certain cells in the eyes or cells with limited sensitivity -Approximately 1 out of 12 males and 1 out of 20 females are colour blind -A person who is colour blind has trouble seeing red, green, blue or mixtures of these colours  most common type: red-green colour blindness -Ishihara test for red-green colour blindness

- Those with normal colour vision should read the number 74

- Those with normal colour vision should read the number 6

-Those with normal colour vision should read the number 29 -Those with red-green deficiencies read the number 70 -Those with total colour blindness can not read any number

-Those with normal colour vision should not be able to read any number -Those with red-green deficiencies read the number 5 -Those with total colour blindness can not read any number

-Low levels of blood plasma clotting factors -The body’s ability to control blood clotting is impaired -Hemophiliac’s can bleed for a long time -May also bleed internally: knees, ankles, elbows - Can range from mild to severe

Males: -100% of daughters will be affected -0% of sons will be affected Heterozygous female: -50% of daughters will be affected -50% of sons will be affected Homozygous female: -100% of daughters will be affected -100% of sons will be affected

-Neurological disorder affecting the peripheral nervous system -Periphery nerves control muscles and relay information from our arms and legs to our brain -Characterized by the progressive loss of muscle tissue and touch sensation across various parts of the body -Symptoms usually begin in your feet and legs but may eventually affect your hands and arms -Foot deformities include high arches and hammertoes

-Hereditary hypophosphate rickets due to low levels of phosphate -Also due to deficiency or impaired metabolism of vitamin D, phosphorus or calcium  May be a result of severe malnutrition, little exposure to sunlight, lactose intolerance, digestive disorders, kidney diseases, or liver diseases -Causes the softening of bones which leads to fractures and deformities -Other symptoms include bone pain, low calcium blood levels and uncontrolled muscle spasms