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Human Heredity 14.1 Human Chromosomes Humans have 46 chromosomes Occurs in 23 pairs (most autosomes) 2 of the 46 are sex-determining chromosomes (X and Y) XX=Female, XY=Male Picture of chromosomes=karyotype Doctors use to determine sex of baby and genetic abnormalities SAMPLE KARYOTYPE Pedigree Chart that shows relationships within families often used to trace lineage of a disease/disorder Circle=Female Square=Male Shaded=Affected __ marriage I children Human Genes Autosomal Recessive Disorders-caused by 2 recessive alleles present (ex: PKU, Tay Sach’s, CF) Autosomal Dominant Disorders-only one allele present causes affliction (ex: dwarfism, Huntington’s Disease) Codominant Alleles-Sickle Cell Recessive Disorders A.Cystic fibrosis: Homozygous recessives (cc) have cystic fibrosis - body cannot make needed chloride channel, high concentrations of extracellular chloride causes mucous to build up, infections, pneumonia. Diet, antibiotics and treatment can extend life to 25 years or more. B.Tay-Sachs: Enzyme that breaks down brain lipids is non-functional in homozygous recessives (tt). Buildup of lipids causes death by age 2-3 Dominant Disorders *Achondroplasia (dwarfism): AA = Homozygous dominant is lethal - fatal (spontaneous abortion of fetus). Aa = dwarfism. aa = no dwarfism. 99.96% of all people in the world are homozygous recessive (aa) Dominant Disorders B. Polydactyly (extra fingers or toes): PP or Pp = extra digits, aa = 5 digits. 98% of all people in the world are homozygous recessive (pp) Co Dominant Alleles ss= sickle cell anemia (misshapen Sickle Cell: many believe sickle cell anemia co evolved with malaria cells lead to death) SS= normal red cells, healthy Ss= not enough sickle cells to kill and resistant to malaria! (body destroys the sickle cells and the parasite)