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Gene Location and Pedigrees

Gene Location and Pedigrees. We refer to genes as either sex-linked (on the sex-determining chromosomes) or autosomal (not on the sex-linked chromosomes). Sex Linkage. Sex-linked traits: traits that are controlled by genes located on the sex chromosomes ex. X-linked recessive:

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Gene Location and Pedigrees

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  1. Gene Location and Pedigrees • We refer to genes as either sex-linked (on the sex-determining chromosomes) or autosomal (not on the sex-linked chromosomes)

  2. Sex Linkage • Sex-linked traits: traits that are controlled by genes located on the sex chromosomes • ex. X-linked recessive: • red-green colourblindness in humans: a recessive allele located on the X gene • More prevalent in males since females would have to inherit 2 recessive alleles to be red-green colourblind • Since males inherit only one X chromosome they require only one recessive allele to be colourblind

  3. Ex. X-linked dominant

  4. Why use Pedigrees? • Punnett squares work well for organisms that have large numbers of offspring and controlled matings, but humans are quite different: 1. Small families - Even large human families have 20 or fewer children. 2. Uncontrolled matings, often with heterozygotes.

  5. Goals of Pedigree Analysis 1. Determine the mode of inheritance: dominant, recessive, sex-linked, autosomal. 2. Determine the probability of an affected offspring for a given cross.

  6. Fraternal Twins Identical Twins Basic Symbols More Symbols

  7. Try and figure out the method of inheritance… X-linked recessive

  8. Try and figure out the method of inheritance… Autosomal recessive

  9. Try and figure out the method of inheritance… X-linked recessive

  10. Case Study: Sickle Cell Anemia • One of the most common genetic diseases that afflicts persons of African ancestry. • about 10% of such persons carry the allele for this trait • in some areas of Africa, upwards of 40% carry the allele • Homozygous individuals with sickle-cell disease suffer from: • “Crises” in joints and bones • Strokes, blindness • Damage to lungs, kidneys or heart

  11. Untreated, many sufferers die before the age of 20 • Modern medical treatments can prolong life to age 40-50 (for individuals who are homozygous for Sickle cell anemia) • Normal allele (A) and Sickle allele (S) are CODOMINANT • In heterozygous individuals (AS), both normal and abnormal hemoglobin are produced • Individuals are usually healthy, but may notice problem in conditions of low oxygen (high altitude) • Known as ‘carriers’

  12. Sickle Cell Disease • What does it actually do? • Affects the structure of hemoglobin • Help bind oxygen in blood, carry to body cells • Hemoglobin becomes ‘sticky’, and red blood cells collapse when there is no oxygen Normal red blood cells Sickled red blood cells

  13. Hemoglobin Hemoglobin subunit Red Blood Cell Oxygen molecule

  14. Sickle cell traits - malaria

  15. CTGACTCCTGAGGAGAAGTCT GACTGAGGACTCCTCTTCAGA CTGACTCCTGTGGAGAAGTCT GACTGAGGACACCTCTTCAGA Effects of Sickle Cell Mutation DNA order of amino acids L T P E E K S L T P V E K S protein shape cell function

  16. Case Study: Sickle Cell Anemia • Why do we see this more often in Africa, especially when it is deadly? • There must be a benefit to having this abnormal allele! • Malaria! • Caused by a blood parasite • Infect red blood cells • When a blood cell with defective hemoglobin are infected, the cells sickle and die • The parasite is trapped and infection is reduced

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