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Human Inheritance A. Pedigree A map or graphic representation of genetic inheritance Used to map genetic disorders Similar to a family tree Use symbols that are shaded, un-shaded or half shaded Lines between two symbols indicate marriage Lines above symbols indicate offspring or siblings = unaffected male = unaffected female = affected female = affected male = female carrier (heterozygous) = male carrier (heterozygous) Parents Siblings (children) 1st born 2nd born B. Simple Recessive Heredity Most disorders are recessive Requires 2 recessive alleles (one from each parent) 1. Cystic Fibrosis Most common among white Americans Caused by a defective protein (mutation in DNA) Causes accumulation of thick mucous production in lungs and digestive tract 2. Tay Sachs Disease Common among Amish and Jews of Eastern European ancestry Caused by the absence of an enzyme that breaks down fat in the central nervous system (mutation in DNA where the code for this enzyme is missing or incorrect) Causes fat to accumulate in the spinal cord and brain and eventually crushes it 3. Phenylketonuria (PKU) Common in people of Norwegian and Swedish ancestry Caused by the absence of an enzyme that converts the amino acid phenylalanine to tyrosine Phenylalanine accumulates and damages the CNS Infants with PKU that drink milk rich in phenylalanine will have mental retardation Treated by altering the diet C. Simple Dominant Heredity Only one allele that codes for the disorder is required 1. Huntington’s Disease Lethal disease that causes the breakdown of certain parts of the brain Onset is not until ages 30-50 If you don’t know your family history you may have had children and passed the disease on to them by the time you are diagnosed D. Sex Determination Inherit one sex chromosome from each parent XX = female (one possible gamete = only X) XY = male (two possible gametes = X or Y) *** It is the male sperm that determines the sex of the child X X X XX XX Y XY XY 50% chance of being female 50% chance of being male 1. Sex-linked Inheritance Traits determined by genes on the sex chromosomes Remember females have matching chromosomes (XX) Males do not have matching chromosomes (XY) Most of the traits are found on the X chromosome a. Color Blindness X X = normal female X Y = normal male X Xc = female carrier Xc Y = color blind male Xc Xc = color blind female Q: What is the probability of having a female child with color blindness with a normal mother and a father who is color blind? X X x Xc Y Xc Y X X Xc X Y X X Xc X Y A: 0% b. Hemophilia X-linked disorder Causes problems with clotting the blood Severe bruising and difficulty stopping the bleeding Occurs more in males than females because males cannot be carriers X X = normal female X Y = normal male X XH = female carrier XH Y = hemophiliac male XH XH = hemophiliac female E. Other Inheritance Disorders and Traits 1. Sickle-Cell Anemia When the red blood cells become sickle shaped (crescent) The hemoglobin (protein) on the red bloods cells is not produced and the RBC cannot carry oxygen This causes anemia and pain to the tissues 2. Blood Typing Blood Types: A, B, AB, O “I” or “i” is the allele used for blood type 3 alleles: IA, IB, i Phenotype Genotype A IA IA or IA i B IB IB or IB i AB IA IB O ii Perform the following crosses 1. Heterozygous A x AB 2. Heterozygous A x Homozygous B 3. AB x AB 4. Heterozygous B x O F. Testing for Genetic Disorders 1. Karyotype: picture used to identify chromosomal abnormalities 22 pairs of autosomal chromosomes (non-sex chromosomes) 1 pair of sex chromosomes