Lecture_13_-_Linkage_Recombination_and_Chromosome_Mapping_-_Ch_7-1

Lecture_13_-_Linkage_Recombination_and_Chromosome_Mapping_-_Ch_7-1

Info iconThis preview shows pages 1–11. Sign up to view the full content.

View Full Document Right Arrow Icon
Lecture 10 Lecture 10 Linkage, Linkage, Recombination & Recombination & Chromosome Mapping Chromosome Mapping
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Linkage and Recombination Linkage and Recombination Linkage refers to phenomenon that some seemingly unrelated traits such as flower color and plant height seem to pass from one generation to another as a unit In other words, these traits don’t seem to follow Mendel’s Law of Independent Assortment Early geneticists struggled to understand this, but now we know it is caused by the fact that the genes that produce these traits are located on the same chromosome
Background image of page 2
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Linkage and Recombination Linkage and Recombination However, we also know that linkage is not absolute. Much experimental evidence exists that linked genes can be separated during meiosis and that new combinations of genes and/or alleles can be formed. This event, called recombination , is the result of homologous chromosomes exchanging pieces of DNA during synapsis in a process called crossing over
Background image of page 4
Background image of page 5

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Linkage and Recombination Linkage and Recombination Linkage and Recombination makes the actual genotypic and phenotypic ratios in the offspring generation different from the expected ratios Example, suppose we have two traits in a plant, flower color and plant height. In a classic Mendelian experiment, crossing pure breeding homozygous parents (one parent is tall with red flowers, the other is dwarf with white flowers), then crossing the F1 hetereozygotes should produce a phenotypic ratio of 9:3:3:1 tall, red to dwarf red to tall, white to dwarf white plants This will be true if the two traits are not linked
Background image of page 6
Linkage and Recombination Linkage and Recombination However, if the two traits are linked, then this phenotypic ratio may be different If we repeat this crossbreeding experiment several times and the phenotypic ratios, although different from the expected, are always the same or similar, then we can determine that the two genes are linked. This altered phenotypic ratio is called a linkage ratio . In other words this is the phenotypic ratio that results from the linkage and is different from the phenotypic ratio expected due to independent assortment
Background image of page 7

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Background image of page 8
Linkage and Recombination Linkage and Recombination However, during the course of the experiments, if one experiment yields phenotypic ratios that are different from the linkage ratio, recombination has probably occurred In other words, recombination ‘ unlinks ’ the two linked genes. The frequency of occurrence of these recombination events provides evidence of the degree of linkage between two genes
Background image of page 9

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Linkage and Recombination Linkage and Recombination The degree of linkage refers to how closely two genes are located on a chromosome. In other words, two genes that are located very close
Background image of page 10
Image of page 11
This is the end of the preview. Sign up to access the rest of the document.

Page1 / 35

Lecture_13_-_Linkage_Recombination_and_Chromosome_Mapping_-_Ch_7-1

This preview shows document pages 1 - 11. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online