BSC 219

9/18/12

Recombination and chromosome mapping

7.1 Linked Genes Do Not Assort Independently

Notation for Crosses with Linkage

Complete Linkage Leads to Nonrecombinant Gametes and Nonrecombinant Progeny

Crossing Over with Linked Genes Lead to Recombiant Gametes and Recombinant Progeny

Calculating Recombination Frequency

Recombination frequency = (number of recombinant progeny / total number of progeny) × 100%

Coupling and Repulsion Configuration of Linked Genes

Coupling (cis configuration): Wild type alleles are found on one chromosome; mutant alleles are found on the other chromosome.

Coupling and Repulsion Configuration of Linked Genes

Repulsion (trans configuration): Wild-type allele and mutant allele are found on the same chromosome.

Testing for Independent Assortment

Gene Mapping with Recombination Frequencies

Genetic maps are determined by recombinant frequency.

Map unit and centiMorgans

Constructing a Genetic Map with Two-Point Testcrosses

Look at combinations

Recombination frequency of 50% suggest genes are on different chromosomes

Use only genes present on same chromosome or linkage group

7.3 A Three-Point Testcross Can Be Used to Map Three Linked Genes

Constructing a Genetic Map with the Three-Point Testcross

Constructing a Genetic Map with the Three-Point Testcross

Determining the gene order

Determining the location of crossovers

Calculating the recombination frequencies

Interference and coefficient of coincidence

Effect of multiple crossovers

Mapping human genes

7.4 Physical Mapping Methods Are Used to Determine the Physical Positions of Genes on Particular Chromosomes

Deletion Mapping

Uses cells with chromosomes that have deleted regions

If gene of interest is in deleted region frequency of inheritance changes

Somatic – Cell Hybridization

Uses hybrid of human and mouse cells

Some human chromosomes are lost in stable cell line

Use multiple cell lines to see which chromosome correlates with gene