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10.2 inheritance

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IB Biology 2015

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10.2 inheritance

  1. 1. 10.2 Inheritance Essential idea: Genes may be linked or unlinked and are inherited accordingly. http://upload.wikimedia.org/wikipedia/c ommons/4/46/Dividing_Cell_Fluorescenc e.jpg http://ies.rayuela.mostoles.educa .madrid.org/deptos/dbiogeo/recu rsos/Apuntes/ApuntesBioBach2/i magenes/genetica/droso.png
  2. 2. Understandings Statement Guidance 10.2 U.1 Gene loci are said to be linked if on the same chromosome. 10.2 U.2 Unlinked genes segregate independently as a result of meiosis. 10.2 U.3 Variation can be discrete or continuous. 10.2 U.4 The phenotypes of polygenic characteristics tend to show continuous variation. 10.2 U.5 Chi-squared tests are used to determine whether the difference between an observed and expected frequency distribution is statistically significant.
  3. 3. Applications and Skills Statement Guidance 10.2 A.1 Morgan’s discovery of non-Mendelian ratios in Drosophila. 10.2 A.2 Completion and analysis of Punnett squares for dihybrid traits. 10.2 A.3 Polygenic traits such as human height may also be influenced by environmental factors. 10.2 S.1 Calculation of the predicted genotypic and phenotypic ratio of offspring of dihybrid crosses involving unlinked autosomal genes. 10.2 S.2 Identification of recombinants in crosses involving two linked genes. Alleles are usually shown side by side in dihybrid crosses, for example, TtBb. In representing crosses involving linkage, it is more common to show them as vertical pairs, 10.2 S.3 Use of a chi-squared test on data from dihybrid crosses.
  4. 4. 10.2 U1 Gene loci are said to be linked if on the same chromosome. • Genes have specific locations (loci) on chromosomes • Chromosomes segregate and assort independently http://web.csulb.edu/~kmacd/361-6-Ch2.htm
  5. 5. 10.2 U2 Unlinked genes segregate independently as a result of meiosis. • Mendel’s law of independent assortment states allele pairs separate independently from other allele pairs during gamete formation (meiosis). • Therefore, traits on different chromosomes are transmitted to the offspring independently of traits on other chromosomes. • An exception to this rule is linked genes https://biologywarakwarak.files.wordpress.com/2011/12/crossingover-rec.jpg
  6. 6. 10.2 U3 Variation can be discrete or continuous. • Discrete Variation is controlled by alleles of a single gene or a small number of genes. The environment has little effect. In this case you either have the characteristic or you don't. Cystic fibrosis is a good example for this; either you have cystic fibrosis or you don’t. • Chi-squared calculations work well when using examples with discrete variation • Continuous Variation is a complete range of phenotypes that can exist from one extreme to the other. Height is an example of continuous variation. Continuous variation is the combined effect of many genes (known as polygenic inheritance) and is often significantly affected by environmental influences. Skin color is another example of continuous variation. http://articles.latimes.com/2013/nov/11/entertainment/la-et- cm-princess-bride-disney-musical-20131111
  7. 7. 10.2 U4 The phenotypes of polygenic characteristics tend to show continuous variation.
  8. 8. 10.2 U4 The phenotypes of polygenic characteristics tend to show continuous variation.
  9. 9. Example: Human skin color • This is controlled by as many as 6 genes each with its own alleles. • As the number of genes increases the amount of phenotypic variation increases. • The alleles control the production of melanin which is a pigment that colors skin. • In this example the calculation is performed with 3 genes each with 3 alleles. The cross is between two individuals heterozygous at both alleles Allele Key A= add melanin a= no melanin added B= adds melanin b= no melanin added 10.2 U4 The phenotypes of polygenic characteristics tend to show continuous variation. http://www2.estrellamountain.edu/faculty/farabee/BIOBK/BioBookgeninteract.html
  10. 10. 10.2 A.3 Polygenic traits such as human height may also be influenced by environmental factors. • Polygenic inheritance occurs when two or more genes control the expression of a phenotype. • As the amount of genes that control one trait increase, the number of phenotypes increases. • Each additional gene has an additive affect, increasing the phenotypes. This is called continuous variation. • Example is human height, which varies from person to person within the same race, and varies between different races. Height shows continuous variation. http://www.buzzle.com/img/articleI mages/345051-59012-35.jpg
  11. 11. 10.2 A.1 Morgan’s discovery of non-Mendelian ratios in Drosophila. Thomas Hunt Morgan Drosophila melanogaster – fruit fly Fast breeding, chromosomes (XX/XY) Discovered sex-linked gene, located on X or Y chromosome. These genes characteristic are not expressed in the same ratios as traits located on other chromosomes.
  12. 12. 10.2 U5 Chi-squared tests are used to determine whether the difference between an observed and expected frequency distribution is statistically significant. • A chi-square test is a statistical test that can be used to determine whether observed frequencies are significantly different from expected frequencies • These statistical tests enable us to compare observed and expected frequencies empirically and to decide if the results we see are statistically significant. Statistical significance in this case implies that the differences are not due to chance alone, but instead may be caused by other factors at work. • The formula to the right is for a chi-squared test O = observed frequencies E = expected frequencies X2 =
  13. 13. 10.2 U5 Chi-squared tests are used to determine whether the difference between an observed and expected frequency distribution is statistically significant.
  14. 14. 10.2 U5 Chi-squared tests are used to determine whether the difference between an observed and expected frequency distribution is statistically significant.
  15. 15. Mendel's Second Law of Independent Assortment • This law states that allele pairs separate independently during the formation of gametes. • Therefore, traits are transmitted to offspring independently of one another 10.2 A.2 Completion and analysis of Punnett squares for dihybrid traits.
  16. 16. Phenotype Key: Phenotypic ratio: – 9 Smooth Yellow: – 3 Smooth green: – 3 Rough Yellow: – 1 Rough Green 10.2 S.1 Calculation of the predicted genotypic and phenotypic ratio of offspring of dihybrid crosses involving unlinked autosomal genes
  17. 17. 10.2 S.1 Calculation of the predicted genotypic and phenotypic ratio of offspring of dihybrid crosses involving unlinked autosomal genes
  18. 18. 10.2 S.1 Calculation of the predicted genotypic and phenotypic ratio of offspring of dihybrid crosses involving unlinked autosomal genes
  19. 19. 10.2 S.1 Calculation of the predicted genotypic and phenotypic ratio of offspring of dihybrid crosses involving unlinked autosomal genes
  20. 20. 10.2 S.1 Calculation of the predicted genotypic and phenotypic ratio of offspring of dihybrid crosses involving unlinked autosomal genes
  21. 21. 10.2 S.1 Calculation of the predicted genotypic and phenotypic ratio of offspring of dihybrid crosses involving unlinked autosomal genes
  22. 22. 10.2 S.1 Calculation of the predicted genotypic and phenotypic ratio of offspring of dihybrid crosses involving unlinked autosomal genes
  23. 23. 10.2 S.1 Calculation of the predicted genotypic and phenotypic ratio of offspring of dihybrid crosses involving unlinked autosomal genes
  24. 24. 10.2 S.3 Use of a chi-squared test on data from dihybrid crosses. • For an example let’s use Mendel’s results from his pea plant crosses • When he did a dihybrid cross between two heterozygotes RrYy x RrYy, the expected phenotypic ratio due to independent assortment would be 9:3:3:1. Look at the chart below to see his actual results.
  25. 25. 10.2 S.3 Use of a chi-squared test on data from dihybrid crosses.
  26. 26. Chi-Square Analysis Practice • Two true-breeding Drosophila are crossed: a normal-winged, red- eyed female and a miniature-winged, vermillion-eyed male. The F1 offspring all have normal wings and red eyes. When the F1 offspring are crossed with miniature-winged, vermillion-eyed flies, the following offspring resulted: – 233 normal wing, red eye – 247 miniature wing, vermillion eye – 7 normal wing, vermillion eye – 13 miniature wing, red eye • What type of conclusions can you draw from this experiment? Explain your answer. 10.2 S.3 Use of a chi-squared test on data from dihybrid crosses.
  27. 27. 10.2 S.2 Identification of recombinants in crosses involving two linked genes. • Link genes are located on the same chromosome and do not sort independently • Genes inherited together • These genes do not show the expected Mendelian ratios as predicted by the Laws Independent Assortment.
  28. 28. Linked Genes 10.2 S.2 Identification of recombinants in crosses involving two linked genes.
  29. 29. 10.2 S.2 Identification of recombinants in crosses involving two linked genes.
  30. 30. 10.2 S.2 Identification of recombinants in crosses involving two linked genes.
  31. 31. 10.2 S.2 Identification of recombinants in crosses involving two linked genes.
  32. 32. 10.2 S.2 Identification of recombinants in crosses involving two linked genes.
  33. 33. 10.2 S.2 Identification of recombinants in crosses involving two linked genes.
  34. 34. 10.2 S.2 Identification of recombinants in crosses involving two linked genes.

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