Human heredity


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Human heredity

  1. 1. Human heredityInheritance of traits
  2. 2. Human chromosomes• 22 pairs of chromosomes called autosomes• 23rd pair are called the sex chromosomes• Males as XY determine the sex of the offspring- ~50% of the time passing X chromosome (female offspring) and ~50% of the time a Y (male offspring)
  3. 3. Sex chromosomes• Females- XX• Males- XY• Not all genes shared• Some genes of the X chromosome are not on the Y• There are a few genes on the Y that are not on the X• Genes that determine maleness are on the y Chromosome• Sex linked genes- are on the sex chromosomes• Recessive traits on the X chromosomes show up more often in males- hemizygous
  4. 4. Male and Female offspring
  5. 5. • Genetic analysis in humans follows a trait for several generations in a family to determine how it is inherited- pedigree analysis• A pedigree shows family information in a chart form. It cab be used as a toll in deterining patterns of inheritance and to help identify disorders.
  6. 6. Pedigree analysis
  7. 7. Karyotype
  8. 8. Spectral karyotyping• Special karyotyping• Each chromosome can have it’s own color• In the near future, each gene can have it’s own color
  9. 9. • Human inheritance involves the interaction of many genes- polygenic inheritance• Expression of traits is also affected by the environment• Multifactorial traits- genes and the environment
  10. 10. • Heteroygotes for recessive traits are often identified because their bodies produce half the amount of gene product, but only homozygous recessive are affected• An allele that codes for a genetic disorder codes for malfunctioning protein or none at all
  11. 11. • Recessive disorders can exhibit the most severe phenotypes because the allele can remain hidden in the heterozygotes• A dominant trait that prevented reproduction would quickly be eliminated from the population, because it could not be passed on
  12. 12. Genetic influences • Inherited genetic diseases • Somatic genetic diseases • Chromosomal aberration
  13. 13. • Genetic analysis of inheritance in humans requires: – Reconstruction of past histories for families – Construction of pedigrees and understanding of inheritance patterns – Modes of inheritance include autosomal dominant, autosomal recessive, X and Y linked inheritance and mitochondrial inheritance
  14. 14. Autosomal Recessive• Cystic fibrosis- mucous production blocks ducts of certain glands• Phenylketonuria- excess accumulation of the amino acid, phenylalanine, in blood to mental retardation• Tay-sachs – improper metabolism of nerve cells causes loss of nerve control• Sickle cell anemia-
  15. 15. Autosomal recessive• Albinism – Absence of pigment in skin, hair, and eyes – All children of affected (homozygous) individuals will be affected – Most affected individuals are the children of unaffected parents
  16. 16. Xeroderma Pigmentosum• Lack of DNA repair• Sensitivity to UV light• Skin cancers• Only about 250 people in the world with this condition
  17. 17. Autosomal Dominant– Marfan syndrome connective tissue defect; death by aortic rupture– Huntington disease- progressive degeneration of nervous system, dementia, and death– Porphyria- episodes of mental derangement and intermittent attacks of pain and dementia
  18. 18. Autosomal dominant • Achondroplasia – (Dwarfism) – Associated with defects in the growth regions of the long bones
  19. 19. • Polydactyly: – Extra fingers or toes• Brachydactyly- malformed hands or shortened fingers – Incomplete penetration and variably expressive
  20. 20. Sex-linked inheritance • Females have two X chromosomes, Males have an X and Y • Lack of genetic equivalence
  21. 21. X-linked Recessive• Color blindness- red or green – insensitivity to red or green light• Muscular dystrophy – Duchenne type progressive, fatal condition
  22. 22. X linked inheritance• Recessive allele• Ichthyosis – Results in skin disorder causing large dark scales to form on body
  23. 23. Hemophilia• Inability for blood to clot due to lack of clotting factor
  24. 24. Additional modes of Inheritance• Y – linked inheritance from father to son – Every Y-linked trait is expressed – Three hundred discovered so far – Mitochondrial inheritance is from mother to offspring • Transmitted through the cytoplasm to the egg • Involve defects in energy conversion and ATP production