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Sex-linked Inheritance

Sex-linked Inheritance. Sex chromosomes determine gender XX : female XY: 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.

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Sex-linked Inheritance

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  1. Sex-linked Inheritance

  2. 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 You already know…

  3. X-linked RECESSIVE Inheritance • 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

  4. Colour blindness • 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

  5. - Those with normal colour vision should read the number 74

  6. - Those with normal colour vision should read the number 6

  7. 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

  8. 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

  9. Hemophilia • 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

  10. X-linked DOMINANT Inheritance • 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

  11. Charcot-Marie Tooth Disease • 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

  12. Rickets • 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

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