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Campbell: Chapter 15 Holtzclaw : pg 111

Please do the following activities on the student media (Chapter 15): - MP3 tutor: Chromosomal Basis of Inheritance - Activity: Polyploid Plants (relate to speciation (sympatric)!!).

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Campbell: Chapter 15 Holtzclaw : pg 111

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  1. Please do the following activities on the student media (Chapter 15): - MP3 tutor: Chromosomal Basis of Inheritance - Activity: Polyploid Plants (relate to speciation (sympatric)!!) Concept 4: Applying the chromosomal basis of inheritance to analysis the effects of alterations in chromosome number or structure. Campbell: Chapter 15 Holtzclaw: pg 111

  2. But First… Linked Genes from last class… A blue fly with silver spots is mated with a wild type fly (grey, no spots) and all of the F1 generation are phenotypically wild (grey, no spots). The F1 fly is mated with a blue fly with silver spots (test cross) with the following results for the testcross offspring:1025 wild type 1002 blue with silver spots 352 grey with silver spots 366 blue with no spots Are the genes for blue and silver spots linked? How do you know? If so, what is the recombination frequency for the genes for blue and silver spots?

  3. But First… Linked Genes from last class… 1025 wild type PARENTAL TYPE 1002 blue with silver spots PARENTAL TYPE 352 grey with silver spots RECOMBINANT 366 blue with no spots RECOMBINANT Are the genes for blue and silver spots linked? YES How do you know? BECAUSE IF IT WAS TRUE INDEPENDENT ASSORTMENT, THE TEST CROSS OF A DOUBLE HETEROZYGOTE AND THE DOUBLE HOMOZYGOUS RECESSIVE WOULD HAVE PRODUCED A 1:1:1:1 RATIO However, the genes are not completely linked… in other words, since some recombinants exist… the chromosomes must have recombined via crossing over…

  4. Video Clip

  5. But First… Linked Genes from last class… 1025 wild type PARENTAL TYPE 1002 blue with silver spots PARENTAL TYPE 352 grey with silver spots RECOMBINANT 366 blue with no spots RECOMBINANT If so, what is the recombination frequency for the genes for blue and silver spots? Recombination frequency = #recombinants/total # of offspring = (365+366)/(1025+1002+352+366) = (731)/(2738) = 0.266 This means that the genes recombine via crossing over 26.6% of the time!

  6. Try This! • Genes A, B, and C are located on the same chromosome. Testcrosses show that the recombination frequency between A and B is 28% and between A and C is 12%. A’s in the middle! Can you determine the linear order of these genes are their relative distance from each other in map units?

  7. Try This! • Genes A, B, and C are located on the same chromosome. Testcrosses show that the recombination frequency between A and B is 28% and between A and C is 12%. Can you determine the linear order of these genes are their relative distance from each other in map units? 28mu 12mu 40 mu B A C

  8. Learning Intentions Goal: to analyze mechanisms of chromosomal inheritance • You must know: • How the chromosome theory of inheritance connects the physical movement of chromosomes in meiosis to Mendel’s laws of inheritance • How alteration of chromosome number or structurally altered chromosomes can cause genetic disorders

  9. Alteration of Chromosome Number • How? Nondisjuction • Occurs when homologous chromosomes do not separate properly during meiosis II. • Result? Aneuploidy • Incorrect number of a chromosome • Trisomic: three copies of the chromosome • Monosomic: one copy of the chromosome • OR: Result? Polyploidy • More than two complete sets of chromosomes

  10. What happens next? What would the haploid gametes look like?

  11. Down’s Syndrome: aneuploidy

  12. Is this individual trisomic or monosomic?

  13. Tetraploid Mammal! Polyploidy

  14. Rearrangement of Chromosome Structure • Portions of a chromosomes may be lost or rearranged during crossing over • Deletion • Fragment is lost. Missing genes. • Duplication • Extra fragment. Extra genes. • Inversion • Backwards section! May affect genes. • Translocation • Moving a piece to a nonhomologous chromosome

  15. Translocation

  16. Chromosaomal Deletion • Example: Cris du Chat • Deletion in chromosome 5 in humans • Small head, unusual facial features, has a cry that sounds like mewing of a distressed cat • Death in infancy or early childhood • Affects 1 in 20,000 or 50,000 of live births

  17. Try This! A spermatocyte produces the following four sperm cells:n + 1 n + 1 n – 1 n – 1 • These cells are the result of which process? • When would this happen?

  18. Try This! A spermatocyte produces the following four sperm cells:n + 1 n + 1 n – 1 n – 1 • These cells are the result of which process? NONDISJUNCTION • When would this happen? DURING MEIOSIS I

  19. Learning Intentions Goal: to analyze mechanisms of chromosomal inheritance • You must know: • How the chromosome theory of inheritance connects the physical movement of chromosomes in meiosis to Mendel’s laws of inheritance • How alteration of chromosome number or structurally altered chromosomes can cause genetic disorders • Try Worksheet! • You should be able to answer all questions on pg 112-114 in Holtzclaw

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