Beyond Dominant and Recessive Alleles Co – Dominance Multiple Alleles Sex – linkage and Traits Polygenic Traits
New Concepts <ul><li>Some alleles are neither dominant nor recessive. </li></ul><ul><li>Many genes have more than two alle...
Co Dominance – Type I <ul><li>Occurs when one allele is not  completely  dominant over the other </li></ul><ul><li>The het...
Example of incomplete dominance:  flower color in snapdragon plants
Another example of incomplete dominance – horse color
Co-Dominance – Type II <ul><li>Both alleles contribute to the phenotype </li></ul><ul><li>Instead of a blend, phenotype sh...
Example of Co dominance <ul><li>Feather color in chickens </li></ul><ul><li>Two alleles:  F B  = Black </li></ul><ul><ul><...
Example of Co dominance:
 
Multiple Alleles <ul><li>Many genes have more than two alleles! </li></ul><ul><li>Does not mean an  individual  can have m...
Multiple Alleles and CoDominance  <ul><li>Human blood typing: </li></ul><ul><ul><li>Multiple allele: A, B, O </li></ul></u...
Possible genotypes and phenotypes <ul><li>Genotype   Phenotype </li></ul>
Sex-Linkage <ul><li>Coded for by genes  on the X chromosome. THERE ARE NO TRAITS FOUND ON THE Y CHROMOSOME. </li></ul><ul>...
Red-green color-blindness:  an example of a sex-linked trait <ul><li>Two possible alleles </li></ul><ul><ul><li>X C  - nor...
 
Possible genotypes and phenotypes <ul><li>Genotype   Phenotype </li></ul>
 
Some Sex linked Traits <ul><li>Colorblindness – Red and Green** </li></ul><ul><li>Hemophilia** </li></ul><ul><li>Some Musc...
Polygenic Traits <ul><li>Traits such as height, weight, and skin color result from the cumulative effects of many genes. <...
Polygenic Traits, cont’d <ul><li>Recognizable by their expression as a gradation of small differences (a continuous variat...
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Genetics 3 other traits ib

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Genetics 3 other traits ib

  1. 1. Beyond Dominant and Recessive Alleles Co – Dominance Multiple Alleles Sex – linkage and Traits Polygenic Traits
  2. 2. New Concepts <ul><li>Some alleles are neither dominant nor recessive. </li></ul><ul><li>Many genes have more than two alleles. </li></ul><ul><li>If a gene is located on the X chromosome (sex-linked), females will have two alleles, but males will only have one. </li></ul>
  3. 3. Co Dominance – Type I <ul><li>Occurs when one allele is not completely dominant over the other </li></ul><ul><li>The heterozygous phenotype is a blending of the two homozygous phenotypes….results in a NEW phenotype </li></ul>
  4. 4. Example of incomplete dominance: flower color in snapdragon plants
  5. 5. Another example of incomplete dominance – horse color
  6. 6. Co-Dominance – Type II <ul><li>Both alleles contribute to the phenotype </li></ul><ul><li>Instead of a blend, phenotype shows distinct features of both alleles – NO NEW PHENOTYPE </li></ul>
  7. 7. Example of Co dominance <ul><li>Feather color in chickens </li></ul><ul><li>Two alleles: F B = Black </li></ul><ul><ul><ul><ul><ul><li>F W = White </li></ul></ul></ul></ul></ul><ul><li>Heterozygous phenotype shows a black – white speckled feather </li></ul>
  8. 8. Example of Co dominance:
  9. 10. Multiple Alleles <ul><li>Many genes have more than two alleles! </li></ul><ul><li>Does not mean an individual can have more than two alleles </li></ul><ul><li>Only means there are more than two possible alleles in the population. </li></ul>
  10. 11. Multiple Alleles and CoDominance <ul><li>Human blood typing: </li></ul><ul><ul><li>Multiple allele: A, B, O </li></ul></ul><ul><ul><li>CoDominace: AB blood type </li></ul></ul>
  11. 12. Possible genotypes and phenotypes <ul><li>Genotype Phenotype </li></ul>
  12. 13. Sex-Linkage <ul><li>Coded for by genes on the X chromosome. THERE ARE NO TRAITS FOUND ON THE Y CHROMOSOME. </li></ul><ul><li>Females have two X chromosomes, so have two alleles for the gene </li></ul><ul><li>Males have one X (and one Y, which doesn’t have the same genes as an X), so males only have one allele for the gene. </li></ul><ul><li>Colorblindness & Hemophilia – recessive trait on X chromosome </li></ul>
  13. 14. Red-green color-blindness: an example of a sex-linked trait <ul><li>Two possible alleles </li></ul><ul><ul><li>X C - normal (dominant) </li></ul></ul><ul><ul><li>X c - color blind (recessive) </li></ul></ul><ul><ul><li>SAMPLE EXAMPLES: </li></ul></ul>
  14. 16. Possible genotypes and phenotypes <ul><li>Genotype Phenotype </li></ul>
  15. 18. Some Sex linked Traits <ul><li>Colorblindness – Red and Green** </li></ul><ul><li>Hemophilia** </li></ul><ul><li>Some Muscular Dystrophies </li></ul><ul><li>Some Respiratory Enzyme Deficiencies </li></ul>
  16. 19. Polygenic Traits <ul><li>Traits such as height, weight, and skin color result from the cumulative effects of many genes. </li></ul><ul><li>These traits are not expressed as “either/or’” as was the case with Mendel’s pea plant traits. </li></ul>
  17. 20. Polygenic Traits, cont’d <ul><li>Recognizable by their expression as a gradation of small differences (a continuous variation). </li></ul><ul><li>Resulting phenotypes form a bell-shape curve. </li></ul>

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