Linkage Summary

Genes are located on chromosomes.

There are thousands of genes but a much smaller number of chromosomes. In eukaryotes there will be more than one gene per chromosome.

That is, many genes will be linked together on a chromosome.

Linkage may be demonstrated by the two gene test cross.

If the RF is less than 50%, the genes are linked.

If the RF is 50%, the genes may be linked or not linked.

The two gene test cross may be used to establish linkage groups.

The two gene test cross may be used to establish gene maps.

For linked genes the F-1 may be in either cis or trans arrangement, as established by the P generation.

Recombination and crossing over are not identical terms.

We deal with inter and intra-chromosomal recombination.

We may have complete or incomplete linkage.

Recombination frequencies are additive within 10 map units.

Recombination frequencies above 10% are an underestimate.

In genetics problems we may determine map distances from test cross data.

We may predict test cross progeny from map information.