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Human Heredity

Human Heredity. 14-1. What does it mean to be human? Compare our species to the rest of the world. Humans have 46 chromosomes 23 pairs One pair inherited from mother One pair inherited from father Two of the 46 chromsomes are sex chromosomes Male XY Female XX

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Human Heredity

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  1. Human Heredity • 14-1

  2. What does it mean to be human? Compare our species to the rest of the world...

  3. Humans have 46 chromosomes • 23 pairs • One pair inherited from mother • One pair inherited from father • Two of the 46 chromsomes are sex chromosomes • Male XY • Female XX • Remaining 44 chromosomes are autosomes • Karotype is a picture of arranged chromosomes in pairs

  4. All human egg cells carry a single X chromosome (23,X) • However, half of all sperm cells carry an X chromosome (23,X) and half carry a Y chromosome (23,Y) • This ensures that just about half of the zygotes will be 46, XX and half will be 46, XY • Complete Punnett Square for Male XY and Female XX

  5. Pedigree Charts • A pedigree chart show the relationships within a family • Genetic counselors analyze pedigree charts to infer genotypes of family members

  6. Genes and the Environment • Someone may have genes for a trait but the environmental conditions will decide if the traited is fully expressed • Example: Someone can have genes for height but if proper nutrition is not given the full potential will not be achieved

  7. Problem solving p. 343

  8. Blood Group Genes • Best known groups are: • ABO blood • Rh blood

  9. Rh Blood • The Rh blood group is determined by a single gene with two alleles; positive and negative • Rh stands for “rhesus monkey” the animal in which hte factor was discovered • The positive (Rh+) allele is dominant, so persons who are Rh+/Rh+ or Rh+/Rh- are said to be Rh positive • Individuals with two Rh- alleles are Rh negative

  10. ABO Blood • There are three alleles • Ia, Ib, and i • Ia and Ib are codominant • These alleles produce molecules known as antigens on the surface of red blood cells • Individuals with alleles Ia and Ib produce both A and B antigens, making them blood type AB • The i allele is recessive

  11. Individuals with alleles IaIa or IaI produce only the A antigen, making them blood types A • Those with IbIb pr Ibi alleles are type B • Those who are homozygous for the i allele (ii) produce no antigen are aid to have blood type O

  12. Autosomal Disorders • Disorders caused by recessive alleles • Albinism – lack of pigment in skin, hair, and eyes • Cystic fibrosis – excess mucus in lungs, digestive tract, liver: increased susceptibility to infections • Galactosemia – accumulation of galactose (a sugar) in tissues; lack of normal skin pigment; mental retardation • Phenylketonuria (PKU) – accumulation of phenylanine in tissues, lack of normal skin pigment; mental retardation • Tay-Sachs disease – lipid accumulation in brain cells; mental deficiency; blindness; death in early childhood

  13. Disorders caused by dominant alleles • Achondroplasia – dwarfism • Huntington’s disease – mental deterioration and uncontrollable movements; symptoms usually appear in middle age • Hypercholesterolemia – excess cholesterol in blood; heart disease

  14. Disorders caused by codominant alleles • Sickle cell disease – misshapen, or sickled, red blood cells; damage to many tissues

  15. In both cystic fibrosis and sickle cell disease, a small change in the DNA of a single gene affects the structure of a protein, causing a serious genetic disorder

  16. Cystic fibrosis • Common with people with genes from Northern Europe • Caused by a recessive allele on chromosome 7 • Severe digestive problems • Produce a thick heavy mucus that clogs their lungs

  17. Cystic fibrosis is caused by • A very small genetic change • Most cases are caused by a deletion of 3 bases in the middle of a sequence for a protein • This protein normally allow chloride ions to pass across biological membranes • The deletion of these 3 bases removes just once amino acid from the large protein, causing it to fold improperly

  18. Because of this the cells do not transport the protein to the cell membrane, and the misfolded protein is destroyed • Unable to transport chloride ions, tissues throughout the body malfunction • People with one normal copy of the allele are unaffected, because they can produce enough of the chloride channel protein to allow their tissues to function properly

  19. Sickle cell disease • Disorder found in African Americans • Sickle cell disease is characterized by the bent and twisted shape of the red blood cells • These sickle-shaped red blood cells are more rigid than normal cells and tend to get stuck in the capillaries, the narrowest blood vessels in the body • As a result, blood stops moving through these vessels in the body

  20. Sickle cell disease produces physical weakness and damage to the brain, heart, and spleen • In some cases it may be fatal • In sickle cell just one DNA base is changed, causing a abnormal hemoglobin to form • Red blood cell takes on a sickle shape and does not carry oxygen well

  21. Why do so many African American carry the sickle cell allele? • Most African American can trace their ancestry to west central Africa • Malaria, a serious parasitic disease in common in the region • People who are heterozygous for the sickle cell allele are generally healthy • In addition they have the benefit of being resistant to malaria • Low oxygen levels cause the RBCs to become sickle shaped • When the body destroys the sickled cells, it also destorys the parasites that cause malaria

  22. Dominant or Recessive? • What makes an allele dominant, recessive, or codominant? • It depends on the nature of a gene’s protein product and its role in the cell

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