Advanced Genetics


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Section 9 Part 2

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Advanced Genetics

  1. 1. Advanced Genetics McCammon Biology I
  2. 2. Mendelian Genetics <ul><li>These are the types of problems we had before Christmas. </li></ul><ul><li>Monohybrid crosses </li></ul><ul><li>Dihybrid crosses </li></ul><ul><li>Test cross </li></ul>
  3. 3. Incomplete Dominance <ul><li>This is a condition in which NEITHER allele for a particular trait is dominant over the other. </li></ul><ul><li>For example: red-flowered snapdragons crossed with white ones yield pink. </li></ul>
  4. 4. Incomplete Dominance <ul><li>For these problems, you should make a key for each problem in addition to the Punnett Square, genotype, and phenotype. </li></ul><ul><li>RR = Red (One of the two traits) </li></ul><ul><li>R’R’ or WW = White (The other trait) </li></ul><ul><li>RR’ or RW = Pink (Blending of the two traits) </li></ul>
  5. 5. ABO Blood Types: A Case of Codominance <ul><li>In codominance, both alleles are expressed in heterozygotes. </li></ul><ul><li>In codominance, instead of NEITHER allele being dominant, BOTH alleles are dominant. </li></ul>
  6. 6. ABO Blood Types: A Case of Codominance <ul><li>For these problems, you should also make a key for each problem in addition to the Punnett Square, genotype, and phenotype. </li></ul><ul><li>F B F B = Black Feathers (One Trait) </li></ul><ul><li>F W F W = White Feathers (The other Trait) </li></ul><ul><li>F B F W = Black and White Speckled Feathers (Heterozygous = spotted) </li></ul>
  7. 7. ABO Blood Types: A Case of Codominance <ul><li>Blood type is determined by markers produced by three genes – This is called multiple alleles. </li></ul><ul><ul><li>I A and I B are each dominant to I, but are codominant to each other. </li></ul></ul><ul><ul><li>Therefore, some persons can express I A and I B and have AB Blood Type. </li></ul></ul>
  8. 8. <ul><li>The four blood types are </li></ul><ul><li>A = I A I A or I A i </li></ul><ul><li>B = I B I B or I B i </li></ul><ul><li>AB = I A I B only </li></ul><ul><li>0 = ii only </li></ul>ABO Blood Types: A Case of Codominance
  9. 9. Autosomes and Sex Chromosomes <ul><li>There are 44 autosomes (22 pairs) and 2 sex chromosomes (1 pair) </li></ul>
  10. 10. Autosomes and Sex Chromosomes <ul><li>Gender is determined by sex chromosomes </li></ul><ul><ul><li>Human females have two X chromosomes </li></ul></ul><ul><ul><li>Human males have one X chromosome and one Y chromosome. </li></ul></ul><ul><ul><li>All normal human eggs carry only one X chromosome </li></ul></ul><ul><ul><li>Half of the sperm carry an X chromosome and the other half carry a Y chromosome. </li></ul></ul>
  11. 11. Autosomes and Sex Chromosomes <ul><li>Sex determination in humans </li></ul><ul><ul><li>If an X bearing sperm fertilizes an X bearing egg, a female results. </li></ul></ul><ul><ul><li>If a Y bearing sperm fertilizes an X bearing egg, a male results. </li></ul></ul><ul><ul><ul><li>XX – female </li></ul></ul></ul><ul><ul><ul><li>XY - male </li></ul></ul></ul>
  12. 12. Sex-Linked Traits <ul><li>Some genes are only found on sex chromosomes. </li></ul><ul><ul><li>Genes for color blindness; gene for male pattern baldness; gene for hemophilia. </li></ul></ul>
  13. 13. Sex-Linked Traits <ul><li>Here are the genotypes and you will need to know: </li></ul><ul><li>X B X B = Normal female </li></ul><ul><li>X B Y = Normal Male </li></ul><ul><li>X B X b = Normal female (but she’s a carrier) </li></ul><ul><li>X b X b = Affected female </li></ul><ul><li>X b Y = Affected female </li></ul><ul><li>Y will not have a letter. </li></ul>
  14. 14. Pedigrees <ul><li>A pedigree is a diagram that shows the history of trait. </li></ul><ul><li>Where Punnett’s squares predict the future, pedigrees map the past. </li></ul>
  15. 15. Pedigrees <ul><li>It is used by geneticists to determine if a trait is sex-liked. </li></ul><ul><ul><li>Squares represent males </li></ul></ul><ul><ul><li>Circles represent females </li></ul></ul><ul><ul><li>A horizontal line represents a mating </li></ul></ul><ul><ul><li>A vertical line represents children </li></ul></ul><ul><ul><li>If the circle or square is shaded in, this means they are affected </li></ul></ul>
  16. 16. Pedigrees <ul><ul><li>A triangle means abortion or miscarriage </li></ul></ul><ul><ul><li>A diamond indicates a person of unknown sex </li></ul></ul><ul><ul><li>A diagonal line through a circle or square means the person is dead. </li></ul></ul><ul><ul><li>A diagonal line through a mating means divorce or the pair is not together anymore. </li></ul></ul><ul><ul><li>The children are listed in birth order. </li></ul></ul><ul><ul><li>Each generation is marked with roman numerals </li></ul></ul><ul><ul><li>Each individual is marked with a number starting at the top left. </li></ul></ul>