5.1 - Molecular Maps - Sequenced Genomes PDF

MOLBIOL/BIOL 2C03 – Genetics Week 5 Faizan Saleem 1 Alleles of linked genes to not assort independently Genes on the same chromosome are called syntenic genes Alleles of syntenic genes can be reshuffled when crossing over occurs to produce recombin...

MOLBIOL/BIOL 2C03 – Genetics Week 5 Faizan Saleem 1 Alleles of linked genes to not assort independently Genes on the same chromosome are called syntenic genes Alleles of syntenic genes can be reshuffled when crossing over occurs to produce recombinant chromosomes Parental chromosomes or non-recombinant chromosomes that do not go under crossing over and carry same alleles as they were transmitted from parents. Syntenic genes that are so close together that their alleles cannot sort independently are called linked genes Genetic linkage mapping plots the positions of genes and their relative distances from each other on chromosomes Not all syntenic genes are linked 2 Patterns of Recombination in Response to Distance Between the Genes 1. Syntenic genes located near each other on a chromosome tend to recombine less often during crossing over, while the farther apart recombine more often. 2. However, syntenic genes located far a part from each other or on different chromosomes assort independently. - syntenic not linked 3 Observations We will Discuss in this Lecture 1. Linked genes are always syntenic. 2. When syntenic genes are so far apart that crossing over generates independent assortment, they are not linked. 3. Genetic Linkage = More parental gametes and less recombinant gametes. 4. Crossing over is less likely to occur between linked genes. 5. The frequency of crossing over is roughly proportionate to the distance between the genes. 4  Review: Unlinked genes assort independently Alleles from each Parent 1 Parent 2 Offspring gene move gametes independently to gametes - located on differ chromosomes. - don't show genetic linkage Offspring Independent assortment predicts each type of gamete will have a frequency of 25% (1:1:1:1) 5  But linked genes do not assort independently Parent 1 Parent 2 Offspring gametes are alleles some ondiffer > - Gametes with parental Offspring linkage are more frequent than gametes with recombined linkage 6  But linked genes do not assort independently Parent 1 Parent 2 Offspring gametes Offspring In this cross, the D allele is linked to the e allele in one parent, and the d allele is linked to the E allele in the 7 other parent  But linked genes do not assort independently Parent 1 Parent 2 Offspring DE de gametes DE de DDEE (DE/DE) ddee (de/de) DE DE DE de de de De De dE dE DE Offspring de A characteristic of genetic linkage is that the recombination between linked genes is low (Parental alleles stay together), leading to more parental gametes. 8 Types of Genetic Linkage 9 Complete Genetic Linkage 1. Complete Genetic Linkage: No recombination or only parental allele combinations in gametes. 2. For example, in cases where a dihybrid cross produces two equally frequent parental allele combinations but no recombinants. - don't want to sort without relying on the other 10 Incomplete Genetic Linkage 1. Incomplete Genetic Linkage: Mixture of parental and non- parental (recombinant) gametes. 2. Frequency of parental gametes is >50% % and for recombinant