11 2,3,4 mendgen part2 2010 for pdf


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11 2,3,4 mendgen part2 2010 for pdf

  1. 1. Mendelian Genetics, part II<br />From Section 11-3, 11-4, 14-1<br />
  2. 2. Beyond simple dominant and recessive alleles (other possibilities out there in the real world).<br />
  3. 3. The real world of genetics<br />Some alleles are neither dominant nor recessive, and many traits are controlled by multiple alleles or multiple genes.<br />
  4. 4. Incomplete dominance<br />Incomplete dominance – neither allele is completely dominant over the other. <br />Therefore, in this case, the heterozygote’s phenotype is in between the two homozygous phenotypes (intermediate phenotype).<br />
  5. 5. Incomplete dominance - snapdragons<br />
  6. 6. Incomplete dominance<br />?<br />Allow these to self-pollinate<br />?<br />
  7. 7.
  8. 8. Incomplete dominance, cont.<br />A brown horse bred with a white horse produces…<br />tan-colored foals<br />
  9. 9. Incomplete dominance<br />Make a Punnett square and give the genotypic and phenotypic ratios for a cross between two heterozygotes for a trait with incomplete dominance. <br />(B allele for black fur, b allele for white fur)<br />
  10. 10. Example: incomplete dominance in fur color<br />BB = Black Fur<br />Bb = Gray Fur<br />Bb = White Fur<br />Parents: Bb x Bb<br />Both gray<br />The heterozygous phenotype is in between the homozygous phenotypes. The alleles are incompletely dominant.<br />
  11. 11. Codominance<br />In codominance, both alleles contribute to the phenotype (neither allele is completely dominant nor completely hidden by the other-it’s a combination).<br />
  12. 12. Codominance in Shorthorn cattle<br />red<br />white<br />×<br />roan<br />
  13. 13. Codominance in Rhododendrons<br />
  14. 14. Codominance<br />Make a Punnett square and give the genotypic and phenotypic ratios for a cross between two heterozygotes for a trait with Codominance. <br />G allele for green leaves, g allele for yellow leaves)<br />
  15. 15. Example: Codominance in leaf color<br />Parents: Gg x Gg<br />Both green and yellow leaves<br />GG = Green<br />Gg = BOTH green and yellow<br />gg = yellow<br />The heterozygous phenotype Expresses both the green and yellow leaf color of the homozygotes. The alleles are codominant.<br />
  16. 16. Multiple Alleles<br />When there are more than two alleles for a gene the trait is said to have multiple alleles.<br />
  17. 17. Multiple Alleles<br />Human blood type is controlled by multiple alleles.<br />There are 3 alleles:<br />IA IB i<br />Two different things are going on—codominance and dominance.<br />codominant<br />Recessive to<br />
  18. 18. What are the possible combinations of the three alleles and what blood types result from each combination?<br />IA IB i<br />
  19. 19. Genotypes and Phenotypes for ABO blood groups (alleles IA, IB, i)<br />Genotypes<br />Phenotypes<br />IA IA<br />IA i<br />IB IB<br />IB i<br />IA IB<br />ii<br />Type A blood<br />Type B blood<br />Type AB blood<br />Type O blood<br />
  20. 20. Polygenic Traits<br />Polygenic traits are those traits that are controlled by two or more genes (poly=many, genic=genes).<br />Polygenic traits often show a wide range of phenotypes.<br />
  21. 21. Multiple Gene (Polygenic) Inheritance of skin color<br />Parent 1 genotype: AaBbCc<br />Parent 2 genotype: AaBbCc<br />Each capital letter represents an allele for dark skin, each lower-case letter represents an allele for light skin. Count the number of capital letters each possible child has to determine the how dark or light their skin would be.<br />
  22. 22. Sex Chromosomes<br />Two of the 46 chromosomes in humans are known as the sex chromosomes.<br />The remaining 44 chromosomes (22 pairs) are known as autosomes.<br />
  23. 23. X and Y chromosomes<br />
  24. 24. end<br />