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Dihybrid Crosses, Gene Linkage and Recombination

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For the IB DP Biology course AHL: Genetics unit. To get the editable pptx file, please make a donation to one of my preferred charities. More information at http://sciencevideos.wordpress.com/about/biology4good/

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Dihybrid Crosses, Gene Linkage and Recombination

  1. 1. Dihybrid Crosses & Gene Linkage<br />Stephen Taylor<br />10.2 Dihybrid Crosses & Gene Linkage<br />1<br />http://sciencevideos.wordpress.com<br />
  2. 2. Mendel’s Law of Independent Assortment<br />“Can you remember it?”<br />10.2 Dihybrid Crosses & Gene Linkage<br />2<br />http://sciencevideos.wordpress.com<br />
  3. 3. Mendel’s Law of Independent Assortment<br />“The presence of an allele of one of the genes in a gamete has no influence over which allele of another gene is present.”<br />This only holds true for unlinked genes (genes on different chromosomes). <br />10.2 Dihybrid Crosses & Gene Linkage<br />3<br />http://sciencevideos.wordpress.com<br />
  4. 4. Mendel’s Law of Independent Assortment<br />“The presence of an allele of one of the genes in a gamete has no influence over which allele of another gene is present.”<br />Key to alleles:<br />Y = yellow<br />y = green<br />S = smooth<br />s = rough<br />This only holds true for unlinked genes (genes on different chromosomes). <br />meiosis<br />sy<br />Sy<br />sY<br />SY<br />10.2 Dihybrid Crosses & Gene Linkage<br />4<br />http://sciencevideos.wordpress.com<br />
  5. 5. Dihybrid Crosses<br />Consider two traits, each carried on separate chromsomes (the genes are unlinked). <br />Key to alleles:<br />Y = yellow<br />y = green<br />S = smooth<br />s = rough<br />In this example of Lathyrusodoratus (sweet pea), <br />we consider two traits: pea colourand pea surface. <br />What is the predicted phenotype ratio for a cross between two pea plants which are heterozygous at both loci?<br />Phenotype:<br />F0<br />Heterozygous at both loci<br />Heterozygous at both loci<br />Genotype:<br />Punnet Grid:<br />F1<br />10.2 Dihybrid Crosses & Gene Linkage<br />5<br />http://sciencevideos.wordpress.com<br />
  6. 6. Dihybrid Crosses<br />Consider two traits, each carried on separate chromsomes (the genes are unlinked). <br />Key to alleles:<br />Y = yellow<br />y = green<br />S = smooth<br />s = rough<br />In this example of Lathyrusodoratus (sweet pea), <br />we consider two traits: pea colourand pea surface. <br />What is the predicted phenotype ratio for a cross between two pea plants which are heterozygous at both loci?<br />Phenotype:<br />Smooth, yellow<br />Smooth, yellow<br />F0<br />Heterozygous at both loci<br />Heterozygous at both loci<br />SsYy<br />SsYy<br />Genotype:<br />Punnet Grid:<br />F1<br />10.2 Dihybrid Crosses & Gene Linkage<br />6<br />http://sciencevideos.wordpress.com<br />
  7. 7. Dihybrid Crosses<br />Consider two traits, each carried on separate chromsomes (the genes are unlinked). <br />Key to alleles:<br />Y = yellow<br />y = green<br />S = smooth<br />s = rough<br />In this example of Lathyrusodoratus (sweet pea), <br />we consider two traits: pea colourand pea surface. <br />What is the predicted phenotype ratio for a cross between two pea plants which are heterozygous at both loci?<br />Phenotype:<br />Smooth, yellow<br />Smooth, yellow<br />F0<br />Heterozygous at both loci<br />Heterozygous at both loci<br />SsYy<br />SsYy<br />Genotype:<br />Punnet Grid:<br />F1<br />10.2 Dihybrid Crosses & Gene Linkage<br />7<br />http://sciencevideos.wordpress.com<br />
  8. 8. Dihybrid Crosses<br />Consider two traits, each carried on separate chromsomes (the genes are unlinked). <br />Key to alleles:<br />Y = yellow<br />y = green<br />S = smooth<br />s = rough<br />In this example of Lathyrusodoratus (sweet pea), <br />we consider two traits: pea colourand pea surface. <br />What is the predicted phenotype ratio for a cross between two pea plants which are heterozygous at both loci?<br />Phenotype:<br />Smooth, yellow<br />Smooth, yellow<br />F0<br />Heterozygous at both loci<br />Heterozygous at both loci<br />SsYy<br />SsYy<br />Genotype:<br />Punnet Grid:<br />F1<br />Phenotypes: 9 Smooth, yellow : 3 Smooth, green : 3 Rough, yellow : 1 Rough, green<br />10.2 Dihybrid Crosses & Gene Linkage<br />8<br />http://sciencevideos.wordpress.com<br />
  9. 9. Dihybrid Crosses<br />Consider two traits, each carried on separate chromsomes (the genes are unlinked). <br />Key to alleles:<br />Y = yellow<br />y = green<br />S = smooth<br />s = rough<br />In this example of Lathyrusodoratus (sweet pea), <br />we consider two traits: pea colourand pea surface. <br />Calculate the predicted phenotype ratio for:<br />Phenotype:<br />F0<br />Heterozygous for S, homozygous dominant for Y <br />Heterozygous at both loci<br />Genotype:<br />Punnet Grid:<br />F1<br />Phenotypes:<br />10.2 Dihybrid Crosses & Gene Linkage<br />9<br />http://sciencevideos.wordpress.com<br />
  10. 10. Dihybrid Crosses<br />Consider two traits, each carried on separate chromsomes (the genes are unlinked). <br />Key to alleles:<br />Y = yellow<br />y = green<br />S = smooth<br />s = rough<br />In this example of Lathyrusodoratus (sweet pea), <br />we consider two traits: pea colourand pea surface. <br />Calculate the predicted phenotype ratio for:<br />Phenotype:<br />Smooth, yellow<br />Smooth, yellow<br />F0<br />Heterozygous for S, homozygous dominant for Y <br />Heterozygous at both loci<br />SsYY<br />SsYy<br />Genotype:<br />Punnet Grid:<br />F1<br />Phenotypes:<br />10.2 Dihybrid Crosses & Gene Linkage<br />10<br />http://sciencevideos.wordpress.com<br />
  11. 11. Dihybrid Crosses<br />Consider two traits, each carried on separate chromsomes (the genes are unlinked). <br />Key to alleles:<br />Y = yellow<br />y = green<br />S = smooth<br />s = rough<br />In this example of Lathyrusodoratus (sweet pea), <br />we consider two traits: pea colourand pea surface. <br />Calculate the predicted phenotype ratio for:<br />Phenotype:<br />Smooth, yellow<br />Smooth, yellow<br />F0<br />Heterozygous for S, homozygous dominant for Y <br />Heterozygous at both loci<br />SsYY<br />SsYy<br />Genotype:<br />Punnet Grid:<br />F1<br />Phenotypes:<br />10.2 Dihybrid Crosses & Gene Linkage<br />11<br />http://sciencevideos.wordpress.com<br />
  12. 12. Dihybrid Crosses<br />Consider two traits, each carried on separate chromsomes (the genes are unlinked). <br />Key to alleles:<br />Y = yellow<br />y = green<br />S = smooth<br />s = rough<br />In this example of Lathyrusodoratus (sweet pea), <br />we consider two traits: pea colourand pea surface. <br />Calculate the predicted phenotype ratio for:<br />Phenotype:<br />Smooth, yellow<br />Smooth, yellow<br />F0<br />Heterozygous for S, homozygous dominant for Y <br />Heterozygous at both loci<br />SsYY<br />SsYy<br />Genotype:<br />Punnet Grid:<br />F1<br />Phenotypes:<br />10.2 Dihybrid Crosses & Gene Linkage<br />12<br />http://sciencevideos.wordpress.com<br />
  13. 13. Dihybrid Crosses<br />Consider two traits, each carried on separate chromsomes (the genes are unlinked). <br />Key to alleles:<br />Y = yellow<br />y = green<br />S = smooth<br />s = rough<br />In this example of Lathyrusodoratus (sweet pea), <br />we consider two traits: pea colourand pea surface. <br />Calculate the predicted phenotype ratio for:<br />Phenotype:<br />Smooth, yellow<br />Smooth, yellow<br />F0<br />Heterozygous for S, homozygous dominant for Y <br />Heterozygous at both loci<br />SsYY<br />SsYy<br />Genotype:<br />Punnet Grid:<br />6 Smooth, yellow : 4 Rough, yellow<br />F1<br />Phenotypes: 3 Smooth, yellow : 2 Rough, yellow<br />Present the ratio in the simplest mathematical form. <br />10.2 Dihybrid Crosses & Gene Linkage<br />13<br />http://sciencevideos.wordpress.com<br />
  14. 14. Dihybrid Crosses<br />Common expected ratios of dihybrid crosses. <br />SsYy<br />SsYy<br />SsYy<br />SsYy<br />Heterozygous at both loci<br />Heterozygous at both loci<br />Heterozygous at both loci<br />Heterozygous at one locus, homozygous dominant at the other<br />3 : 2<br />9 : 3 : 3 : 1<br />Ssyy<br />SsYy<br />SSyy<br />ssYY<br />= All SsYy<br />Heterozygous at both loci<br />Heterozygous/<br />Homozygous recessive<br />SSYY<br />ssyy<br />= all SyYy<br />Ssyy<br />ssYy<br />= 1 : 1 : 1 : 1<br />4 : 3 : 1<br />10.2 Dihybrid Crosses & Gene Linkage<br />14<br />http://sciencevideos.wordpress.com<br />
  15. 15. Dihybrid Crosses<br />Consider two traits, each carried on separate chromsomes (the genes are unlinked). <br />Key to alleles:<br />Y = yellow<br />y = green<br />S = smooth<br />s = rough<br />In this example of Lathyrusodoratus (sweet pea), <br />we consider two traits: pea colourand pea surface. <br />A rough yellow pea is test crossed to determine its genotype.<br />Phenotype:<br />F0<br />Rough, yellow<br />Genotype:<br />Punnet Grid:<br />F1<br />Phenotypes:<br />10.2 Dihybrid Crosses & Gene Linkage<br />15<br />http://sciencevideos.wordpress.com<br />
  16. 16. Dihybrid Crosses<br />Consider two traits, each carried on separate chromsomes (the genes are unlinked). <br />Key to alleles:<br />Y = yellow<br />y = green<br />S = smooth<br />s = rough<br />In this example of Lathyrusodoratus (sweet pea), <br />we consider two traits: pea colourand pea surface. <br />A rough yellow pea is test crossed to determine its genotype.<br />Phenotype:<br />F0<br />Rough, yellow<br />ssYy<br />Genotype:<br />Punnet Grid:<br />F1<br />Phenotypes:<br />10.2 Dihybrid Crosses & Gene Linkage<br />16<br />http://sciencevideos.wordpress.com<br />
  17. 17. Dihybrid Crosses<br />Consider two traits, each carried on separate chromsomes (the genes are unlinked). <br />Key to alleles:<br />Y = yellow<br />y = green<br />S = smooth<br />s = rough<br />In this example of Lathyrusodoratus (sweet pea), <br />we consider two traits: pea colourand pea surface. <br />A rough yellow pea is test crossed to determine its genotype.<br />Phenotype:<br />F0<br />Rough, yellow<br />ssYy or ssYY<br />Genotype:<br />Punnet Grid:<br />F1<br />Phenotypes:<br />10.2 Dihybrid Crosses & Gene Linkage<br />17<br />http://sciencevideos.wordpress.com<br />
  18. 18. Dihybrid Crosses<br />Consider two traits, each carried on separate chromsomes (the genes are unlinked). <br />Key to alleles:<br />Y = yellow<br />y = green<br />S = smooth<br />s = rough<br />In this example of Lathyrusodoratus (sweet pea), <br />we consider two traits: pea colourand pea surface. <br />A rough yellow pea is test crossed to determine its genotype.<br />Phenotype:<br />F0<br />Rough, yellow<br />ssYy or ssYY<br />ssyy<br />Genotype:<br />Punnet Grid:<br />F1<br />Phenotypes:<br />Remember: A test cross is the unknown with a known homozygous recessive. <br />10.2 Dihybrid Crosses & Gene Linkage<br />18<br />http://sciencevideos.wordpress.com<br />
  19. 19. Dihybrid Crosses<br />Consider two traits, each carried on separate chromsomes (the genes are unlinked). <br />Key to alleles:<br />Y = yellow<br />y = green<br />S = smooth<br />s = rough<br />In this example of Lathyrusodoratus (sweet pea), <br />we consider two traits: pea colourand pea surface. <br />A rough yellow pea is test crossed to determine its genotype.<br />Phenotype:<br />F0<br />Rough, yellow<br />ssYy or ssYY<br />ssyy<br />Genotype:<br />Punnet Grid:<br />F1<br />Phenotypes:<br />10.2 Dihybrid Crosses & Gene Linkage<br />19<br />http://sciencevideos.wordpress.com<br />
  20. 20. Dihybrid Crosses<br />Consider two traits, each carried on separate chromsomes (the genes are unlinked). <br />Key to alleles:<br />Y = yellow<br />y = green<br />S = smooth<br />s = rough<br />In this example of Lathyrusodoratus (sweet pea), <br />we consider two traits: pea colourand pea surface. <br />A rough yellow pea is test crossed to determine its genotype.<br />Phenotype:<br />F0<br />Rough, yellow<br />ssYy or ssYY<br />ssyy<br />Genotype:<br />Punnet Grid:<br />F1<br />Phenotypes:<br />Some green peas will be present in the offspring if the unknown parent genotype is ssYy. <br />No green peas will be present in the offspring if the unknown parent genotype is ssYY. <br />10.2 Dihybrid Crosses & Gene Linkage<br />20<br />http://sciencevideos.wordpress.com<br />
  21. 21. Dihybrid Crosses<br />Consider two traits, each carried on separate chromsomes (the genes are unlinked). <br />Key to alleles:<br />Y = yellow<br />y = green<br />S = smooth<br />s = rough<br />In this example of Lathyrusodoratus (sweet pea), <br />we consider two traits: pea colourand pea surface. <br />A smooth green pea is test crossed. Deduce the genotype. <br />Smooth green = nine offspring. Rough green = one offspring. <br />Phenotype:<br />F0<br />Smooth, green<br />Genotype:<br />Punnet Grid:<br />F1<br />Phenotypes:<br />10.2 Dihybrid Crosses & Gene Linkage<br />21<br />http://sciencevideos.wordpress.com<br />
  22. 22. Dihybrid Crosses<br />Consider two traits, each carried on separate chromsomes (the genes are unlinked). <br />Key to alleles:<br />Y = yellow<br />y = green<br />S = smooth<br />s = rough<br />In this example of Lathyrusodoratus (sweet pea), <br />we consider two traits: pea colourand pea surface. <br />A smooth green pea is test crossed. Deduce the genotype. <br />Smooth green = nine offspring. Rough green = one offspring. <br />Phenotype:<br />F0<br />Smooth, green<br />ssyy<br />Genotype:<br />Punnet Grid:<br />F1<br />Phenotypes:<br />10.2 Dihybrid Crosses & Gene Linkage<br />22<br />http://sciencevideos.wordpress.com<br />
  23. 23. Dihybrid Crosses<br />Consider two traits, each carried on separate chromsomes (the genes are unlinked). <br />Key to alleles:<br />Y = yellow<br />y = green<br />S = smooth<br />s = rough<br />In this example of Lathyrusodoratus (sweet pea), <br />we consider two traits: pea colourand pea surface. <br />A smooth green pea is test crossed. Deduce the genotype. <br />Smooth green = nine offspring. Rough green = one offspring. <br />Phenotype:<br />F0<br />Smooth, green<br />SSyy<br />ssyy<br />Genotype:<br />Punnet Grid:<br />F1<br />Phenotypes:<br />10.2 Dihybrid Crosses & Gene Linkage<br />23<br />http://sciencevideos.wordpress.com<br />
  24. 24. Dihybrid Crosses<br />Consider two traits, each carried on separate chromsomes (the genes are unlinked). <br />Key to alleles:<br />Y = yellow<br />y = green<br />S = smooth<br />s = rough<br />In this example of Lathyrusodoratus (sweet pea), <br />we consider two traits: pea colourand pea surface. <br />A smooth green pea is test crossed. Deduce the genotype. <br />Smooth green = nine offspring. Rough green = one offspring. <br />Phenotype:<br />F0<br />Smooth, green<br />SSyy or Ssyy<br />ssyy<br />Genotype:<br />Punnet Grid:<br />F1<br />Phenotypes:<br />10.2 Dihybrid Crosses & Gene Linkage<br />24<br />http://sciencevideos.wordpress.com<br />
  25. 25. Dihybrid Crosses<br />Consider two traits, each carried on separate chromsomes (the genes are unlinked). <br />Key to alleles:<br />Y = yellow<br />y = green<br />S = smooth<br />s = rough<br />In this example of Lathyrusodoratus (sweet pea), <br />we consider two traits: pea colourand pea surface. <br />A smooth green pea is test crossed. Deduce the genotype. <br />Smooth green = nine offspring. Rough green = one offspring. <br />Phenotype:<br />F0<br />Smooth, green<br />SSyy or Ssyy<br />ssyy<br />Genotype:<br />Punnet Grid:<br />F1<br />Phenotypes:<br />No rough peas will be present in the offspring if the unknown parent genotype is SSyy. <br />The presence of rough green peas in the offspring means that the unknown genotype must be Ssyy. <br />The expected ratio in this cross is 3 smooth green : 1 rough green. This is not the same as the outcome. Remember that each reproduction event is chance and the sample size is very small. With a much larger sample size, the outcome would be closer to the expected ratio, simply due to probability. <br />10.2 Dihybrid Crosses & Gene Linkage<br />25<br />http://sciencevideos.wordpress.com<br />
  26. 26. Sooty the Guinea Pig<br />Key to alleles*:<br />C = colour c = albino<br />A = agouti a = black<br />R = round ears r = pointy ears<br />L = long whiskers l = short whiskers<br />S = soft fur s = rough fur<br />N = sharp nails n = smooth nails<br />Sooty news story from the BBC:<br />http://news.bbc.co.uk/2/hi/uk_news/wales/1048327.stm<br />* C and A genes are real. The rest are made up for this story. <br />10.2 Dihybrid Crosses & Gene Linkage<br />26<br />http://sciencevideos.wordpress.com<br />
  27. 27. Sooty the Guinea Pig<br />Key to alleles:<br />S = soft fur s = rough fur<br />N = sharp nails n = smooth nails<br />Sooty has soft fur and sharp nails. <br />In one of his matings with a rough-furred, smooth-nailed female, the following guinea piglets are produced:<br />6 x rough fur, sharp nails; 3 x soft fur sharp nails. <br />DeduceSooty’s genotype. <br />Phenotype:<br />Rough fur, smooth nails<br />Soft fur, sharp nails<br />F0<br />Genotype: <br />Punnet Grid:<br />F1<br />Phenotypes:<br />10.2 Dihybrid Crosses & Gene Linkage<br />27<br />http://sciencevideos.wordpress.com<br />
  28. 28. Sooty the Guinea Pig<br />Key to alleles:<br />S = soft fur s = rough fur<br />N = sharp nails n = smooth nails<br />Sooty has soft fur and sharp nails. <br />In one of his matings with a rough-furred, smooth-nailed female, the following guinea piglets are produced:<br />6 x rough fur, sharp nails; 3 x soft fur sharp nails. <br />DeduceSooty’s genotype. <br />Phenotype:<br />Rough fur, smooth nails<br />Soft fur, sharp nails<br />F0<br />Genotype: ssnn<br />Punnet Grid:<br />F1<br />Phenotypes:<br />10.2 Dihybrid Crosses & Gene Linkage<br />28<br />http://sciencevideos.wordpress.com<br />
  29. 29. Sooty the Guinea Pig<br />Key to alleles:<br />S = soft fur s = rough fur<br />N = sharp nails n = smooth nails<br />Sooty has soft fur and sharp nails. <br />In one of his matings with a rough-furred, smooth-nailed female, the following guinea piglets are produced:<br />6 x rough fur, sharp nails; 3 x soft fur sharp nails. <br />DeduceSooty’s genotype. <br />Phenotype:<br />Rough fur, smooth nails<br />Soft fur, sharp nails<br />F0<br />Genotype: ssnn SSNN or SsNN or SsNn<br />Punnet Grid:<br />F1<br />Phenotypes:<br />10.2 Dihybrid Crosses & Gene Linkage<br />29<br />http://sciencevideos.wordpress.com<br />
  30. 30. Sooty the Guinea Pig<br />Key to alleles:<br />S = soft fur s = rough fur<br />N = sharp nails n = smooth nails<br />Sooty has soft fur and sharp nails. <br />In one of his matings with a rough-furred, smooth-nailed female, the following guinea piglets are produced:<br />6 x rough fur, sharp nails; 3 x soft fur sharp nails. <br />DeduceSooty’s genotype. <br />Phenotype:<br />Rough fur, smooth nails<br />Soft fur, sharp nails<br />F0<br />Genotype: ssnn SSNN or SsNN or SsNn<br />Punnet Grid:<br />F1<br />Soft fur<br />Sharp nails<br />Soft fur<br />Smooth nails<br />Rough fur<br />Sharp nails<br />Rough fur<br />Smooth nails<br />Phenotypes:<br />10.2 Dihybrid Crosses & Gene Linkage<br />30<br />http://sciencevideos.wordpress.com<br />
  31. 31. Sooty the Guinea Pig<br />Key to alleles:<br />S = soft fur s = rough fur<br />N = sharp nails n = smooth nails<br />Sooty has soft fur and sharp nails. <br />In one of his matings with a rough-furred, smooth-nailed female, the following guinea piglets are produced:<br />6 x rough fur, sharp nails; 3 x soft fur sharp nails. <br />DeduceSooty’s genotype. <br />Phenotype:<br />Rough fur, smooth nails<br />Soft fur, sharp nails<br />F0<br />Genotype: ssnn SSNN or SsNN or SsNn<br />Punnet Grid:<br />F1<br />Soft fur<br />Sharp nails<br />Soft fur<br />Smooth nails<br />Rough fur<br />Sharp nails<br />Rough fur<br />Smooth nails<br />Phenotypes:<br />Only these two phenotypes have been produced. <br />Sooty has only produced SN and sN gametes. <br />10.2 Dihybrid Crosses & Gene Linkage<br />31<br />http://sciencevideos.wordpress.com<br />
  32. 32. Sooty the Guinea Pig<br />Key to alleles:<br />S = soft fur s = rough fur<br />N = sharp nails n = smooth nails<br />Sooty has soft fur and sharp nails. <br />In one of his matings with a rough-furred, smooth-nailed female, the following guinea piglets are produced:<br />6 x rough fur, sharp nails; 3 x soft fur sharp nails. <br />DeduceSooty’s genotype. <br />Phenotype:<br />Rough fur, smooth nails<br />Soft fur, sharp nails<br />F0<br />Genotype: ssnn SSNN or SsNN or SsNn<br />Punnet Grid:<br />F1<br />Soft fur<br />Sharp nails<br />Soft fur<br />Smooth nails<br />Rough fur<br />Sharp nails<br />Rough fur<br />Smooth nails<br />Phenotypes:<br />Only these two phenotypes have been produced. <br />Sooty has only produced SN and sN gametes. <br />It is most likely that his genotype is SsNN. <br />10.2 Dihybrid Crosses & Gene Linkage<br />32<br />http://sciencevideos.wordpress.com<br />
  33. 33. Sooty the Guinea Pig<br />Key to alleles:<br />R = round ears r = pointy ears<br />L = long whiskers l = short whiskers<br />DeduceSooty’s genotype.<br />Offspring = five with pointy ears and long whiskers <br />Phenotype:<br />Pointy ears, short whiskers<br />Pointy ears, long whiskers<br />F0<br />Genotype: <br />Punnet Grid:<br />F1<br />Phenotypes:<br />10.2 Dihybrid Crosses & Gene Linkage<br />33<br />http://sciencevideos.wordpress.com<br />
  34. 34. Sooty the Guinea Pig<br />Key to alleles:<br />R = round ears r = pointy ears<br />L = long whiskers l = short whiskers<br />DeduceSooty’s genotype.<br />Offspring = five with pointy ears and long whiskers <br />Phenotype:<br />Pointy ears, short whiskers<br />Pointy ears, long whiskers<br />F0<br />Genotype: rrllrrLL or rrLl<br />Punnet Grid:<br />F1<br />Phenotypes:<br />10.2 Dihybrid Crosses & Gene Linkage<br />34<br />http://sciencevideos.wordpress.com<br />
  35. 35. Sooty the Guinea Pig<br />Key to alleles:<br />R = round ears r = pointy ears<br />L = long whiskers l = short whiskers<br />DeduceSooty’s genotype.<br />Offspring = five with pointy ears and long whiskers <br />Phenotype:<br />Pointy ears, short whiskers<br />Pointy ears, long whiskers<br />F0<br />Genotype: rrllrrLL or rrLl<br />Punnet Grid:<br />F1<br />Pointy ears<br />Long whiskers<br />Pointy ears<br />Short whiskers<br />Phenotypes:<br />10.2 Dihybrid Crosses & Gene Linkage<br />35<br />http://sciencevideos.wordpress.com<br />
  36. 36. Sooty the Guinea Pig<br />Key to alleles:<br />R = round ears r = pointy ears<br />L = long whiskers l = short whiskers<br />DeduceSooty’s genotype.<br />Offspring = five with pointy ears and long whiskers <br />Phenotype:<br />Pointy ears, short whiskers<br />Pointy ears, long whiskers<br />F0<br />Genotype: rrllrrLL or rrLl<br />Punnet Grid:<br />F1<br />Pointy ears<br />Long whiskers<br />Pointy ears<br />Short whiskers<br />Phenotypes:<br />Only this phenotype has been produced. <br />Sooty has only produced rL gametes. <br />10.2 Dihybrid Crosses & Gene Linkage<br />36<br />http://sciencevideos.wordpress.com<br />
  37. 37. Sooty the Guinea Pig<br />Key to alleles:<br />R = round ears r = pointy ears<br />L = long whiskers l = short whiskers<br />DeduceSooty’s genotype.<br />Offspring = five with pointy ears and long whiskers <br />Phenotype:<br />Pointy ears, short whiskers<br />Pointy ears, long whiskers<br />F0<br />Genotype: rrllrrLL or rrLl<br />Punnet Grid:<br />F1<br />Pointy ears<br />Long whiskers<br />Pointy ears<br />Short whiskers<br />Phenotypes:<br />Only this phenotype has been produced. <br />Sooty has only produced rL gametes. <br />It is most likely that his genotype is rrLL. <br />10.2 Dihybrid Crosses & Gene Linkage<br />37<br />http://sciencevideos.wordpress.com<br />
  38. 38. Gene Interaction<br />The expression of one gene is dependent upon the prior expression of another.<br />10.2 Dihybrid Crosses & Gene Linkage<br />38<br />http://sciencevideos.wordpress.com<br />
  39. 39. Gene Interaction<br />The expression of one gene is dependent upon the prior expression of another.<br />Key to alleles:<br />C = colour c = albino<br />A = agouti a = black<br />In the case of guinea pigs, there is gene interaction for fur colour. <br />The first gene, C, determines whether colour is present. <br />The second gene, A, is only expressed if C is first expressed. <br />It determines which colourwill be produced.<br />10.2 Dihybrid Crosses & Gene Linkage<br />39<br />http://sciencevideos.wordpress.com<br />
  40. 40. Gene Interaction<br />The expression of one gene is dependent upon the prior expression of another.<br />Key to alleles:<br />C = colour c = albino<br />A = agouti a = black<br />In the case of guinea pigs, there is gene interaction for fur colour. <br />The first gene, C, determines whether colour is present. <br />The second gene, A, is only expressed if C is first expressed. <br />It determines which colourwill be produced.<br />Genotypes<br />ccAA<br />ccAa<br />ccaa<br />CCAA<br />CcAa<br />CCaa<br />Ccaa<br />If the genotype ‘cc’ is present, there will be no expression of colour. <br />A will also not be expresssed. <br />10.2 Dihybrid Crosses & Gene Linkage<br />40<br />http://sciencevideos.wordpress.com<br />
  41. 41. Gene Interaction<br />The expression of one gene is dependent upon the prior expression of another.<br />Key to alleles:<br />C = colour c = albino<br />A = agouti a = black<br />In the case of guinea pigs, there is gene interaction for fur colour. <br />The first gene, C, determines whether colour is present. <br />The second gene, A, is only expressed if C is first expressed. <br />It determines which colourwill be produced.<br />Phenotype ratios do not fit the normal 9 : 3 : 3 : 1 ratio. <br />Genotypes<br />ccAA<br />ccAa<br />ccaa<br />CCAA<br />CcAa<br />CCaa<br />Ccaa<br />If the genotype ‘cc’ is present, there will be no expression of colour. <br />A will also not be expresssed. <br />9 agouti : 3 black : 4 albino<br />10.2 Dihybrid Crosses & Gene Linkage<br />41<br />http://sciencevideos.wordpress.com<br />
  42. 42. Autosomes and Sex Chromosomes<br />Humans have 23 pairs of chromosomes in diploid somatic cells (n=2). <br />22 pairs of these are autosomes, which are homologous pairs. <br />One pair is the sex chromosomes. <br />XX gives the female gender, XY gives male. <br />Karyotype of a human male, showing X and Y chromosomes:<br />http://en.wikipedia.org/wiki/Karyotype<br />SRY<br />The X chromosome is much larger than the Y. <br />X carries many genes in the non-homologous region which are not present on Y.<br />The presence and expression of the SRY gene on Y leads to male development. <br />Chromosome images from Wikipedia:<br />http://en.wikipedia.org/wiki/Y_chromosome<br />10.2 Dihybrid Crosses & Gene Linkage<br />42<br />http://sciencevideos.wordpress.com<br />
  43. 43. Autosomal Gene Linkage vs Sex-Linked Disorders<br />Sex-linked disorders are carried on the non-homologous regions<br />of the X chromosome. <br />Alleles are expressed whether they are dominant or recessive, as there is no alternate allele carried on the Y chromosome. <br />Gene-related disorders which are sex-linked include red-green colour blindness and hemophilia. <br />Males are more frequently affected by sex-linked disorders. <br />A<br />B<br />SCN5A<br />a<br />b<br />(voltage-gated sodium channel)<br />Linked genes are pairs or groups of genes which are inherited together, carried on the same chromosome. <br />Locus 1<br />Locus 2<br />PDCD10<br />Y X<br />(programmed cell death)<br />SOX2<br />(transcription factor - promoter region)<br />There are about 2000 genes on X and 86 on Y.<br />Gene linkage is therefore also common on X and Y. <br />Chromosome 3 from:<br />http://en.wikipedia.org/wiki/Chromosome_3_%28human%29<br />10.2 Dihybrid Crosses & Gene Linkage<br />43<br />http://sciencevideos.wordpress.com<br />
  44. 44. Autosomal Gene Linkage<br />Linked genes are pairs or groups of genes which are inherited together, carried on the same chromosome. <br />10.2 Dihybrid Crosses & Gene Linkage<br />44<br />http://sciencevideos.wordpress.com<br />
  45. 45. Autosomal Gene Linkage<br />Linked genes are pairs or groups of genes which are inherited together, carried on the same chromosome. <br />SCN5A<br />(voltage-gated sodium channel)<br />The SCN5A, PDCD10 and SOX2 genes <br />are all linked by being on chromosome 3. <br />They are a linkage group, and alleles of each will therefore be inherited together. <br />Independent assortment does not occurbetween linked genes. <br />PDCD10<br />(programmed cell death)<br />SOX2<br />(transcription factor - promoter region)<br />Chromosome 3 from:<br />http://en.wikipedia.org/wiki/Chromosome_3_%28human%29<br />10.2 Dihybrid Crosses & Gene Linkage<br />45<br />http://sciencevideos.wordpress.com<br />
  46. 46. Autosomal Gene Linkage<br />Linked genes are pairs or groups of genes which are inherited together, carried on the same chromosome. <br />Standard notation for linked genes:<br />A<br />B<br />“heterozygous at both loci”<br />SCN5A<br />a<br />b<br />(voltage-gated sodium channel)<br />The line denotes the chromosome, or the fact that the two genes are linked. <br />Locus 1<br />Locus 2<br />The SCN5A, PDCD10 and SOX2 genes <br />are all linked by being on chromosome 3. <br />They are a linkage group, and alleles of each will therefore be inherited together. <br />Independent assortment does not occurbetween linked genes. <br />Syllabus examples of Linkage Groups: <br />Sweet peas (Lathyrusodoratus):<br />flower colour(P/p)<br />linked with pollen grain shape (L/l)<br />Corn (Zea mays):<br /> Kernel colour(C/c) <br />linked with Waxiness of kernels (W/w)<br />PDCD10<br />(programmed cell death)<br />SOX2<br />(transcription factor - promoter region)<br />Chromosome 3 from:<br />http://en.wikipedia.org/wiki/Chromosome_3_%28human%29<br />10.2 Dihybrid Crosses & Gene Linkage<br />46<br />http://sciencevideos.wordpress.com<br />
  47. 47. Notation of Gene Linkage<br />Linked genes are pairs or groups of genes which are inherited together, carried on the same chromosome. <br />The genes A and B are linked. <br />The genotype of an individual is AaBb (“heterozygous at both loci”.) <br />10.2 Dihybrid Crosses & Gene Linkage<br />47<br />http://sciencevideos.wordpress.com<br />
  48. 48. Notation of Gene Linkage<br />Linked genes are pairs or groups of genes which are inherited together, carried on the same chromosome. <br />The genes A and B are linked. <br />The genotype of an individual is AaBb (“heterozygous at both loci”.) <br />So in questions or problems you will be given the standard notation or enough information to be able to deduce which allele is on which chromosome. <br />Confusing! <br />Could be..<br />Standard notation:<br />The line denotes the chromosome, or the fact that the two genes are linked. <br />10.2 Dihybrid Crosses & Gene Linkage<br />48<br />http://sciencevideos.wordpress.com<br />
  49. 49. Notation of Gene Linkage<br />Linked genes are pairs or groups of genes which are inherited together, carried on the same chromosome. <br />The genes A and B are linked. <br />The genotype of an individual is AaBb (“heterozygous at both loci”.) <br />A<br />B<br />A<br />b<br />So in questions or problems you will be given the standard notation or enough information to be able to deduce which allele is on which chromosome. <br />a<br />b<br />a<br />B<br />Confusing! <br />Could be..<br />Standard notation:<br />The line denotes the chromosome, or the fact that the two genes are linked. <br />Locus 1<br />Locus 1<br />Locus 2<br />Locus 2<br />Alternative notation:<br />Ab/aB<br />Alternative notation:<br />AB/ab<br />10.2 Dihybrid Crosses & Gene Linkage<br />49<br />http://sciencevideos.wordpress.com<br />
  50. 50. Linkage Groups<br />Are carried on the same chromosomeand are inherited together. They do not assort independently. <br />In sweet peas (Lathyrusodoratus), the genes for flower colour and pollen grain shape are carried on the same chromosome. <br />Plants which are heterozygous at both loci are test-crossed. <br />What ratio of phenotypes is expected?<br />Key to alleles:<br />P = purple p = white<br />L = long l = short<br />Genotype: <br />Phenotype:<br />Image: 'Sweet Pea' http://www.flickr.com/photos/69166981@N00/3600419425<br />10.2 Dihybrid Crosses & Gene Linkage<br />50<br />http://sciencevideos.wordpress.com<br />
  51. 51. Linkage Groups<br />Are carried on the same chromosomeand are inherited together. They do not assort independently. <br />In sweet peas (Lathyrusodoratus), the genes for flower colour and pollen grain shape are carried on the same chromosome. <br />Plants which are heterozygous at both loci are test-crossed. <br />What ratio of phenotypes is expected?<br />Key to alleles:<br />P = purple p = white<br />L = long l = short<br />p<br />l<br />Locus 1<br />Locus 2<br />p<br />l<br />Genotype: <br />Phenotype:<br />White; Short<br />Image: 'Sweet Pea' http://www.flickr.com/photos/69166981@N00/3600419425<br />10.2 Dihybrid Crosses & Gene Linkage<br />51<br />http://sciencevideos.wordpress.com<br />
  52. 52. Linkage Groups<br />Are carried on the same chromosomeand are inherited together. They do not assort independently. <br />In sweet peas (Lathyrusodoratus), the genes for flower colour and pollen grain shape are carried on the same chromosome. <br />Plants which are heterozygous at both loci are test-crossed. <br />What ratio of phenotypes is expected?<br />Key to alleles:<br />P = purple p = white<br />L = long l = short<br />P<br />L<br />p<br />l<br />Locus 1<br />Locus 1<br />Locus 2<br />Locus 2<br />p<br />l<br />p<br />l<br />Genotype: <br />Phenotype:<br />Purple; Long<br />White; Short<br />Image: 'Sweet Pea' http://www.flickr.com/photos/69166981@N00/3600419425<br />10.2 Dihybrid Crosses & Gene Linkage<br />52<br />http://sciencevideos.wordpress.com<br />
  53. 53. Linkage Groups<br />Are carried on the same chromosomeand are inherited together. They do not assort independently. <br />In sweet peas (Lathyrusodoratus), the genes for flower colour and pollen grain shape are carried on the same chromosome. <br />Plants which are heterozygous at both loci are test-crossed. <br />What ratio of phenotypes is expected?<br />Key to alleles:<br />P = purple p = white<br />L = long l = short<br />P<br />L<br />p<br />l<br />Locus 1<br />Locus 1<br />Locus 2<br />Locus 2<br />p<br />l<br />p<br />l<br />Genotype: <br />Phenotype:<br />Purple; Long<br />White; Short<br />Punnet Grid:<br />Phenotypes:<br />Ratio:<br />Image: 'Sweet Pea' http://www.flickr.com/photos/69166981@N00/3600419425<br />10.2 Dihybrid Crosses & Gene Linkage<br />53<br />http://sciencevideos.wordpress.com<br />
  54. 54. Linkage Groups<br />Are carried on the same chromosomeand are inherited together. They do not assort independently. <br />In sweet peas (Lathyrusodoratus), the genes for flower colour and pollen grain shape are carried on the same chromosome. <br />Plants which are heterozygous at both loci are test-crossed. <br />What ratio of phenotypes is expected?<br />Key to alleles:<br />P = purple p = white<br />L = long l = short<br />P<br />L<br />p<br />l<br />Locus 1<br />Locus 1<br />Locus 2<br />Locus 2<br />p<br />l<br />p<br />l<br />Genotype: <br />Phenotype:<br />Purple; Long<br />White; Short<br />Punnet Grid:<br />Purple; Long<br />White; Short<br />Phenotypes:<br />Ratio: 1 : 1<br />Image: 'Sweet Pea' http://www.flickr.com/photos/69166981@N00/3600419425<br />10.2 Dihybrid Crosses & Gene Linkage<br />54<br />http://sciencevideos.wordpress.com<br />
  55. 55. Linkage Groups<br />Are carried on the same chromosomeand are inherited together. They do not assort independently. <br />In sweet peas (Lathyrusodoratus), the genes for flower colour and pollen grain shape are carried on the same chromosome. <br />Plants which are heterozygous at both loci are test-crossed. <br />A small number of purple;short and white;long individuals have appeared in the offspring. Explain what has happened. <br />Key to alleles:<br />P = purple p = white<br />L = long l = short<br />Image: 'Sweet Pea' http://www.flickr.com/photos/69166981@N00/3600419425<br />10.2 Dihybrid Crosses & Gene Linkage<br />55<br />http://sciencevideos.wordpress.com<br />
  56. 56. Recombination <br />of alleles occurs as a result of crossing-over between non-sister chromatids. Exchange of alleles gives new genotypes of gametes.<br />Key to alleles:<br />P = purple p = white<br />L = long l = short<br />Plants which are heterozygous at both loci are test-crossed. <br />A small number of purple;short and white;long individuals have appeared in the offspring. Explain what has happened. <br />Diploid cell<br />Heterozygous at both loci<br />10.2 Dihybrid Crosses & Gene Linkage<br />56<br />http://sciencevideos.wordpress.com<br />
  57. 57. Recombination <br />of alleles occurs as a result of crossing-over between non-sister chromatids. Exchange of alleles gives new genotypes of gametes.<br />Key to alleles:<br />P = purple p = white<br />L = long l = short<br />Plants which are heterozygous at both loci are test-crossed. <br />A small number of purple;short and white;long individuals have appeared in the offspring. Explain what has happened. <br />Possible gametes:<br />The test cross individual is homozygous recessive at both loci, so only one type of gamete is produced. <br />Test individual:<br />p<br />l<br />Heterozygous individual:<br />Diploid cell<br />Heterozygous at both loci<br />Chromosomes replicate in Synthesis phase<br />10.2 Dihybrid Crosses & Gene Linkage<br />57<br />http://sciencevideos.wordpress.com<br />
  58. 58. Recombination <br />of alleles occurs as a result of crossing-over between non-sister chromatids. Exchange of alleles gives new genotypes of gametes.<br />Key to alleles:<br />P = purple p = white<br />L = long l = short<br />Plants which are heterozygous at both loci are test-crossed. <br />A small number of purple;short and white;long individuals have appeared in the offspring. Explain what has happened. <br />P<br />L<br />P<br />L<br />Possible gametes:<br />The test cross individual is homozygous recessive at both loci, so only one type of gamete is produced. <br />Test individual:<br />p<br />l<br />Alleles segregate in meiosis, giving two possible gametes:<br />Heterozygous individual:<br />p<br />l<br />p<br />l<br />Diploid cell<br />Heterozygous at both loci<br />Chromosomes replicate in Synthesis phase<br />10.2 Dihybrid Crosses & Gene Linkage<br />58<br />http://sciencevideos.wordpress.com<br />
  59. 59. Recombination <br />of alleles occurs as a result of crossing-over between non-sister chromatids. Exchange of alleles gives new genotypes of gametes.<br />Key to alleles:<br />P = purple p = white<br />L = long l = short<br />Plants which are heterozygous at both loci are test-crossed. <br />A small number of purple;short and white;long individuals have appeared in the offspring. Explain what has happened. <br />P<br />L<br />Possible gametes:<br />Test individual:<br />p<br />l<br />Heterozygous individual:<br />p<br />l<br />Diploid cell<br />Heterozygous at both loci<br />Chromosomes replicate in Synthesis phase<br />Crossing Over<br />Prophase I<br />Alleles are exchanged<br />Crossing-over occurs occasionally. It is more likely to happen between linked genes which are further apart. <br />10.2 Dihybrid Crosses & Gene Linkage<br />59<br />http://sciencevideos.wordpress.com<br />
  60. 60. Recombination <br />of alleles occurs as a result of crossing-over between non-sister chromatids. Exchange of alleles gives new genotypes of gametes.<br />Key to alleles:<br />P = purple p = white<br />L = long l = short<br />Plants which are heterozygous at both loci are test-crossed. <br />A small number of purple;short and white;long individuals have appeared in the offspring. Explain what has happened. <br />P<br />L<br />P<br />l<br />Possible gametes:<br />Test individual:<br />p<br />l<br />Heterozygous individual:<br />p<br />l<br />Recombinants:<br />Diploid cell<br />Heterozygous at both loci<br />Chromosomes replicate in Synthesis phase<br />Crossing Over<br />Prophase I<br />Alleles are exchanged<br />Sister chromatids are separated in anaphase II.<br />Recombined gametes are produced. <br />p<br />L<br />Crossing-over occurs occasionally. It is more likely to happen between linked genes which are further apart. <br />10.2 Dihybrid Crosses & Gene Linkage<br />60<br />http://sciencevideos.wordpress.com<br />
  61. 61. Recombination <br />of alleles occurs as a result of crossing-over between non-sister chromatids. Exchange of alleles gives new genotypes of gametes.<br />Key to alleles:<br />P = purple p = white<br />L = long l = short<br />Plants which are heterozygous at both loci are test-crossed. <br />A small number of purple;short and white;long individuals have appeared in the offspring. Explain what has happened. <br />P<br />L<br />P<br />l<br />Normal gametes<br />(majority)<br />Possible gametes:<br />Test individual:<br />p<br />l<br />Heterozygous individual:<br />p<br />l<br />Recombinants:<br />p<br />L<br />Crossing-over occurs occasionally. It is more likely to happen between linked genes which are further apart. <br />10.2 Dihybrid Crosses & Gene Linkage<br />61<br />http://sciencevideos.wordpress.com<br />
  62. 62. Recombination <br />of alleles occurs as a result of crossing-over between non-sister chromatids. Exchange of alleles gives new genotypes of gametes.<br />Key to alleles:<br />P = purple p = white<br />L = long l = short<br />Plants which are heterozygous at both loci are test-crossed. <br />A small number of purple;short and white;long individuals have appeared in the offspring. Explain what has happened. <br />P<br />L<br />P<br />l<br />Normal gametes<br />(majority)<br />Possible gametes:<br />Test individual:<br />p<br />l<br />Heterozygous individual:<br />Purple; long<br />White, short<br />p<br />l<br />Recombinants:<br />p<br />L<br />Crossing-over occurs occasionally. It is more likely to happen between linked genes which are further apart. <br />10.2 Dihybrid Crosses & Gene Linkage<br />62<br />http://sciencevideos.wordpress.com<br />
  63. 63. Recombination <br />of alleles occurs as a result of crossing-over between non-sister chromatids. Exchange of alleles gives new genotypes of gametes.<br />Key to alleles:<br />P = purple p = white<br />L = long l = short<br />Plants which are heterozygous at both loci are test-crossed. <br />A small number of purple;short and white;long individuals have appeared in the offspring. Explain what has happened. <br />P<br />L<br />P<br />l<br />Normal gametes<br />(majority)<br />Recombinant gametes<br />(small number)<br />Possible gametes:<br />Test individual:<br />p<br />l<br />Heterozygous individual:<br />White, long<br />Purple; long<br />White, short<br />Purple; short<br />p<br />l<br />Recombinants:<br />p<br />L<br />Crossing-over occurs occasionally. It is more likely to happen between linked genes which are further apart. <br />10.2 Dihybrid Crosses & Gene Linkage<br />63<br />http://sciencevideos.wordpress.com<br />
  64. 64. Crossing-Over<br />Increases genetic variation through recombination of linked alleles. <br />Synapsis<br />Homologous chromosomes associate<br />Chiasma Formation<br />Neighbouring non-sister chromatids are cut at the same point. <br />A Holliday junction forms as the DNA of the cut sections attach to the open end of the opposite non-sister chromatid. <br />Recombination<br />As a result, alleles are swapped between non-sister chromatids. <br />10.2 Dihybrid Crosses & Gene Linkage<br />64<br />http://sciencevideos.wordpress.com<br />
  65. 65. Crossing-Over<br />Increases genetic variation through recombination of linked alleles. <br />10.2 Dihybrid Crosses & Gene Linkage<br />65<br />http://sciencevideos.wordpress.com<br />
  66. 66. Gene Linkage & Recombination<br />The further apart a pair of alleles are on a chromosome, the more likely it is that crossing over may occur between them - leading to recombination.<br />Knowing this, researchers can map the position of genes on a chromosome based on the frequency of recombination between gene pairs: the further apart they are, the more often they cross over. <br />SCN5A<br />(voltage-gated sodium channel)<br />Crossing-over is more likely to occur between SCN5A and PDCD10 than between PDCD10 and SOX2. <br />PDCD10<br />(programmed cell death)<br />SOX2<br />(transcription factor - promoter region)<br />Chromosome 3 from:<br />http://en.wikipedia.org/wiki/Chromosome_3_%28human%29<br />Animation and quiz from:<br />http://www.csuchico.edu/~jbell/Biol207/animations/recombination.html<br />10.2 Dihybrid Crosses & Gene Linkage<br />66<br />http://sciencevideos.wordpress.com<br />
  67. 67. Gene Linkage & Recombination<br />Which description best fits this image? <br />Four chromosomes, four chiasmata<br />Four chromatids, two chiasmata, two centromeres<br />Two chromosomes, four chiasmata<br />A pair of sister chromatids<br />10.2 Dihybrid Crosses & Gene Linkage<br />67<br />http://sciencevideos.wordpress.com<br />
  68. 68. Gene Linkage & Recombination<br />Which description best fits this image? <br />Four chromosomes, four chiasmata<br />Four chromatids, two chiasmata, two centromeres<br />Two chromosomes, four chiasmata<br />A pair of sister chromatids<br />10.2 Dihybrid Crosses & Gene Linkage<br />68<br />http://sciencevideos.wordpress.com<br />
  69. 69. Gene Linkage & Recombination<br />Which description best fits this image? <br />chiasmata<br />Sister chromatids<br />Chromosome 1a<br />Chromosome 1b<br />Sister chromatids<br />centromeres<br />Four chromosomes, four chiasmata<br />Four chromatids, two chiasmata, two centromeres<br />Two chromosomes, four chiasmata<br />A pair of sister chromatids<br />10.2 Dihybrid Crosses & Gene Linkage<br />69<br />http://sciencevideos.wordpress.com<br />
  70. 70. Gene Linkage & Recombination<br />The genes for kernel colour and waxiness are linked in the corn plant (Zea mays). In a cross between a plant that is homozygous dominant at both loci with a plant that is heterozygous at both loci (CW/cw), identify the following genotypes as:<br /> a: regularb:recombinantsc: impossible<br />CcWwCCWwCcWW CCWW CCwwccWW<br />10.2 Dihybrid Crosses & Gene Linkage<br />70<br />http://sciencevideos.wordpress.com<br />
  71. 71. Gene Linkage & Recombination<br />The genes for kernel colour and waxiness are linked in the corn plant (Zea mays). In a cross between a plant that is homozygous dominant at both loci with a plant that is heterozygous at both loci (CW/cw), identify the following genotypes as:<br /> a: regularb:recombinantsc: impossible<br />Key to alleles:<br />C = coloured c = no colour<br />W = waxy w = not waxy<br />CcWwCCWwCcWW CCWW CCwwccWW<br />C<br />W<br />C<br />W<br />Regular gametes<br />(majority)<br />Recombinant gametes<br />(small number)<br />10.2 Dihybrid Crosses & Gene Linkage<br />71<br />http://sciencevideos.wordpress.com<br />
  72. 72. Gene Linkage & Recombination<br />The genes for kernel colour and waxiness are linked in the corn plant (Zea mays). In a cross between a plant that is homozygous dominant at both loci with a plant that is heterozygous at both loci (CW/cw), identify the following genotypes as:<br /> a: regularb:recombinantsc: impossible<br />Key to alleles:<br />C = coloured c = no colour<br />W = waxy w = not waxy<br />CcWwCCWwCcWW CCWW CCwwccWW<br />C<br />W<br />C<br />W<br />c<br />w<br />C<br />W<br />Regular gametes<br />(majority)<br />Recombinant gametes<br />(small number)<br />10.2 Dihybrid Crosses & Gene Linkage<br />72<br />http://sciencevideos.wordpress.com<br />
  73. 73. Gene Linkage & Recombination<br />The genes for kernel colour and waxiness are linked in the corn plant (Zea mays). In a cross between a plant that is homozygous dominant at both loci with a plant that is heterozygous at both loci (CW/cw), identify the following genotypes as:<br /> a: regularb:recombinantsc: impossible<br />Key to alleles:<br />C = coloured c = no colour<br />W = waxy w = not waxy<br />CcWwCCWwCcWWCCWWCCwwccWW<br />C<br />W<br />C<br />W<br />c<br />w<br />C<br />W<br />Regular gametes<br />(majority)<br />Recombinant gametes<br />(small number)<br />10.2 Dihybrid Crosses & Gene Linkage<br />73<br />http://sciencevideos.wordpress.com<br />
  74. 74. Gene Linkage & Recombination<br />The genes for kernel colour and waxiness are linked in the corn plant (Zea mays). In a cross between a plant that is homozygous dominant at both loci (CW/CW) with a plant that is heterozygous at both loci (CW/cw), identify the following genotypes as:<br /> a: regularb:recombinantsc: impossible<br />Key to alleles:<br />C = coloured c = no colour<br />W = waxy w = not waxy<br />CcWwCCWwCcWWCCWWCCwwccWW<br />C<br />C<br />W<br />C<br />W<br />w<br />c<br />w<br />c<br />W<br />C<br />W<br />Regular gametes<br />(majority)<br />Recombinant gametes<br />(small number)<br />10.2 Dihybrid Crosses & Gene Linkage<br />74<br />http://sciencevideos.wordpress.com<br />
  75. 75. Gene Linkage & Recombination<br />E<br />m<br />Two genes are linked as shown here <br />e<br />M<br />The genes are far apart such that crossing-over between the alleles occurs occasionally. Which statement is true of the gametes?<br /> A. All of the gametes will be Em and eM<br /> B. There will be equal numbers of EM, EM, eM and em<br /> C. There will be approximately equal numbers of EM and eM gametes<br /> D. There will be more Em gametes than em gametes<br />10.2 Dihybrid Crosses & Gene Linkage<br />75<br />http://sciencevideos.wordpress.com<br />
  76. 76. Gene Linkage & Recombination<br />E<br />m<br />Two genes are linked as shown here <br />e<br />M<br />The genes are far apart such that crossing-over between the alleles occurs occasionally. Which statement is true of the gametes?<br /> A. All of the gametes will be Em and eM<br /> B. There will be equal numbers of EM, EM, eM and em<br /> C. There will be approximately equal numbers of EM and eM gametes<br /> D. There will be more Em gametes than em gametes<br />10.2 Dihybrid Crosses & Gene Linkage<br />76<br />http://sciencevideos.wordpress.com<br />
  77. 77. Gene Linkage & Recombination<br />E<br />m<br />Two genes are linked as shown here <br />e<br />M<br />The genes are far apart such that crossing-over between the alleles occurs occasionally. Which statement is true of the gametes?<br /> A. All of the gametes will be Em and eM<br /> B. There will be equal numbers of EM, EM, eM and em<br /> C. There will be approximately equal numbers of EM and eM gametes<br /> D. There will be more Em gametes than em gametes<br />E<br />m<br />E<br />M<br />m<br />e<br />e<br />M<br />Regular gametes<br />(majority)<br />Recombinant gametes<br />(small number)<br />10.2 Dihybrid Crosses & Gene Linkage<br />77<br />http://sciencevideos.wordpress.com<br />
  78. 78. For more IB Biology resources:<br />http://sciencevideos.wordpress.com<br />This presentation is free to view. Please make a donation to one of my chosen charities at Gifts4Good and I will send you the editable pptx file.<br />Click here for more information about Biology4Good charity donations. <br />10.2 Dihybrid Crosses & Gene Linkage<br />78<br />This is a Creative Commons presentation. It may be linked and embedded but not sold or re-hosted. <br />

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