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Midterm

Midterm. Friday - or - Monday? Covers Chapters 1,2 and 3.6 If yed, it will mean moving Exam 2 to May 6. Sex Chromosomes. ... ‘X’ and ‘Y’ chromosomes that determine the sex of an individual in many organisms, Females: XX Males: XY. a. a. A. Differential Region. Differential Region.

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Midterm

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  1. Midterm Friday - or - Monday? Covers Chapters 1,2 and 3.6 If yed, it will mean moving Exam 2 to May 6.

  2. Sex Chromosomes ...‘X’ and ‘Y’ chromosomes that determine the sex of an individual in many organisms, Females: XX Males: XY

  3. a a A Differential Region Differential Region Paring Region Paring Region XX: female male

  4. a hemizygous: condition where gene is present in only one dose. male

  5. X Linkage …the pattern of inheritance resulting from genes located on the X chromosome.

  6. X-Linked Genes …refers specifically to genes on the X-chromosome, with no homologs on the Y chromosome.

  7. P x Blue Female Pink Male Gametes or

  8. Gametes or F1 Blue Female Blue Male

  9. F1 x Blue Female Blue Male Gametes or or

  10. Gametes or or F2 Blue Female Blue Male Blue Female Pink Male

  11. F2 Blue Female Blue Male Blue Female Pink Male 3 : 1

  12. P x Pink Female Blue Male Gametes or

  13. Gametes or F1 Blue Female Pink Male

  14. Gametes or or F2 Pink Female Pink Male Blue Female Blue Male

  15. F2 Pink Female Pink Male Blue Female Blue Male 1 1 1 1

  16. Sex Linkage to Ponder • Female is homozygous recessive X-linked gene, • what percentage of male offspring will express? • what percentage of female offspring will express if, • mate is hemizygous for the recessive allele? • mate is hemizygous for the dominant allele? • Repeat at home with female heterozygous X-linked gene!

  17. Sex-Linked vs. Autosomal • autosomal chromosome: non-sex linked chromosome, • autosomal gene: a gene on an autosomal chromosome, • autosomes segregate identically in reciprocal crosses.

  18. X-Linked Recessive TraitsCharacteristics • Many more males than females show the phenotype, • female must have both parents carrying the allele, • male only needs a mother with the allele, • Few (or none) of the offspring of affected males show the disorder, • all of his daughters are carriers, • half of the sons born to these daughters are carriers.

  19. X-Linked Dominant • Affected males married to unaffected females pass the phenotype to their daughters, but not to their sons, • Heterozygous females married to unaffected males pass the phenotype on to half their sons and daughters, • Homozygous dominant females pass the phenotype on to all their sons and daughters,

  20. Autosomal Dominant • Phenotypes appear in every generation, • Affected males and females pass the phenotype to equal proportions of their sons and daughters.

  21. Pedigree for Very Rare Trait 1/2 1/2 Recessive? ---> Yes! 1/2 x 1/2 x ? 1/2 = 1/8 Autosomal? X-Linked? ---> Yes!

  22. Linkage • Genes located on the same chromosome segregate together and are said to be linked.

  23. Independent Assortment A a B b 2n = 4 A A a B b B a b

  24. A A a A a a B B b b Meiosis Prophase I cont. Chiasmata and crossing over

  25. 2n = 1 MeiosisNo Cross Over A a Parent Cell B b A A a a B B b b Daughter Cells Have Parental Chromosomes

  26. 2n = 1 MeiosisWith Cross Over A a Parent Cell B b A A a a B b B b Daughter Cells Have Recombinant Chromosomes

  27. .25 .25 .25 .25 Gamate Formation in F1 Dihybrids P: GGWW x ggww F1 Genotype: GgWw G g W w alleles gametes GW Gw gW gw probability

  28. GW Gw gW gw .25 .25 .25 .25 How do you test for assortment of alleles? F1: GgWw

  29. Test Cross • phenotypes of the offspring indicate the genotype of the gametes produced by the parent in question.

  30. Test CrossGgWw x ggww GW (.25) gw (1) GgWw (.25) Gw (.25) gw (1) G gww (.25) gW (.25) gw (1) ggWw (.25) gw (.25) gw (1) ggww (.25)

  31. P R R P parental types GgWw and gwgw P: GGWW and ggww recombinant types Ggww and ggWw Test CrossGgWw x ggww GW (.25) gw (1) GgWw (.25) Gw (.25) gw (1) Ggww (.25) gW (.25) gw (1) ggWw (.25) gw (.25) gw (1) ggww (.25)

  32. Recombination Frequency …or Linkage Ratio: the percentage of recombinant types, • if 50%, then the genes are not linked, • if less than 50%, then linkage is observed.

  33. Linkage • Genes located on the same chromosome do not recombine, • unless crossing over occurs, • The recombination frequency gives an estimate of the distance between the genes.

  34. Recombination Frequencies • Genes that are adjacent have a recombination frequency near 0%, • Genes that are very far apart on a chromosome have a linkage ratio of 50%, • The relative distance between linked genes influences the amount of recombination observed.

  35. Dihybrid Cross phenotype genotype gametes genotype yellow/round green/wrinkled GGWW x ggww GW gw GgWw P F1

  36. Questions • Don’t rely on the answers in the back of the book to solve your problems… • Don’t just solve them, but understand the principles needed to solve them. • More practice questions are online. No answers are available, i.e. confirm your own answers

  37. a b f c e d

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