Linkage and Gene MapsLinkage and Gene Maps

Mendelian GeneticsMendelian Genetics

Gene LinkageGene Linkage

Thomas Hunt Morgan discovered from his Thomas Hunt Morgan discovered from his study with fruit flies, that genes are “linked” study with fruit flies, that genes are “linked” togethertogether1. Each chromosome is actually a group of 1. Each chromosome is actually a group of

linked geneslinked genes2. Chromosomes assort independently of one 2. Chromosomes assort independently of one

another, not genes.another, not genes.

Crossing Over influence on Crossing Over influence on GeneticsGenetics

Crossing over during Meiosis sometimes Crossing over during Meiosis sometimes separates genes that had been on the separates genes that had been on the same chromosome onto homologous same chromosome onto homologous chromosomes.chromosomes.

Crossing over enevents occasionally Crossing over enevents occasionally separate and exchange linked genes separate and exchange linked genes and produce new combinations of and produce new combinations of alleles. THIS HELPS GENERATE alleles. THIS HELPS GENERATE GENETIC DIVERSITYGENETIC DIVERSITY!!!!!!!!

Gene MapsGene Maps A student in Morgan’s lab, Alfred Sturtevant, A student in Morgan’s lab, Alfred Sturtevant,

wondered if rates of crossing over between wondered if rates of crossing over between genes in meiosis was a clue into gene genes in meiosis was a clue into gene separation. separation.

He created a He created a gene mapgene map, which shows the , which shows the locations of each known gene on one locations of each known gene on one chromosome. chromosome.

What he found was that the further apart two What he found was that the further apart two genes were on a chromosome, the more likely genes were on a chromosome, the more likely they were to separate during crossing over. The they were to separate during crossing over. The closer the 2 genes were, the less likely they closer the 2 genes were, the less likely they were to separate during crossing over. were to separate during crossing over.