1 / 12

Gene Linkage

Gene Linkage. Chapter 19.2 Page 635-641. Gene Linkage and Crossover. Back to Morgan and the fruit flies first Morgan crossed wild-type body colour ( AA ) and straight wings ( BB ) with black body colour ( aa ) and curved wings ( bb ) AABB x aabb

gyala
Download Presentation

Gene Linkage

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Gene Linkage Chapter 19.2 Page 635-641

  2. Gene Linkage and Crossover Back to Morgan and the fruit flies • first Morgan crossed wild-type body colour (AA) and straight wings (BB) with black body colour (aa) and curved wings (bb) AABB x aabb • the F1 generation is heterozygous for both traits AaBb • Morgan then crossed the F1 generation and expected the Mendelian ratio of 9:3:3:1 for a dihybrid cross. • instead all the individuals with wild-type body colour had straight wings and all those with black body colour had curved wings.

  3. Gene Linkage and Crossover • Morgan concluded that the two genes: • did not undergo independent segregation • for this to happen genes would have to be on the same chromosome • the genes are linked

  4. Gene Linkage and Crossover • because the genes are linked the two gametes form an individual that is heterozygous for both traits. • Morgan predicted that crossing the F1 generation would produce an F2 generation what would have a 3:1 phenotypic ratio (3 flies with wildtype body type and straight wings)

  5. Linked genes

  6. Crossing over • Morgan observed that in a small number of dihybrid crosses the offspring had different combinations of traits than the parents Data:

  7. Crossing Over • the new combinations of alleles that Morgan observed came about by DNA crossing over during meiosis.

  8. Crossing Over and Chromosome Mapping • there are groups of linked genes on a chromosome. • these are called a linkage group • particular genes are always found on the same location (locus) on a chromosome. • Morgan showed that the frequency of crossovers between any two genes in a linkage group is always the same. • the frequency of crossing over between any two genes can be stated as a percent.

  9. crossover percentage = (number of recombinations/total number of offspring) x 100% using the previous table’s data: crossover % = 18/400 x 100% crossover % = 4.5% • geneticists use this number to say the two alleles are 4.5 map units apart.

  10. probability = (genotype looking for)/ (total number of possible genotypes) probability = (phenotype looking for)/ (total number of possible phenotype)

  11. Homework! • Review sample question page 638 • Complete Lab Exercise 19.B page 639-640 – Due next class!

More Related