how are genetic and physical maps made?

Question

A question was asked
"Briefly describe how genetic and physical maps of a genome are constructed,
indicating techniques that are used, and how they have been used in genome sequencing projects"


My answer would be genetic maps are made by cloning cut fragments of DNA into vectors and sequecing. The locations of these fragments on each chromosome would be know because they would be linked to genetic markers such as microsatelites. They have been used in genome sequencing projects because the allow a refrence to which further genomic sequencing can by done by overlaping clones of the marker DNA.
Is there anything I could add missing?

Answer 1

First you must understand that a genetic map is the physical representation of the lineal order of the genes in a chromosome, and it is unidirectional, a line for eukaryote and a circle for bacteria. It's really very simple, so simple in fact, that the first person to do so was Thomas Morgan, the one working with fruit flies, and he obviously didn't have a way of sequencing. You could sequence, but that would be too slow, so here's how you do it. You take a considerable number of offspring, where you have identified 2 genes (for 2 point mapping, 3 point mapping is similar) and you are going to calculate the distance between them. These genes must intercross, otherwise you wouldn't have recombination. Then you must determine the parental phenotype (for example AAgg and aaGG) and the recombinant phenotypes. Then you substitute the data (the numbers you counted) in the following formula: (number of recombining phenotypes / total offspring) x 100. A substitution would be something like this: 48/556 x 100 = 8.48 % of recombination. The number you get is the percentage of recombination, and this number marks the distance between the two genes in units known as centiMorgans or map units. In the example, the map would be:
a g
-l-------------l--
8.48 cM

The map is really just a line with the genes indicated (you don't use capital letters because that is the distance between the genes, with either allele, dominant or recesive).

Answer 2

You have only mentioned Genetic Maps above and to this you could add the commonly used DNA markers, such as RFLP's, VNTR's and Microsatellite Polymorphisms and SNP's.

Genetic Maps are used as a Framework for Physical Map Construction. The Genetic map is used for the creation of more detailed human genome maps,called physical maps, they further define the DNA sequence between genetic markers and are essential to the rapid identification of genes.

There are different kinds of physical maps and they measure different things.

Physical maps can be divided into three general types: chromosomal or cytogenetic maps which are based on the banding patterns and are used to locate genetic markers.

RH (Radiation Hybrid) maps show estimates of distance between genetic and physical markers, and are able to provide more precise information regarding the distance between markers than can a linkage map.

The physical map that provides the most detail is the sequence map. Sequence maps show genetic markers, as well as the sequence between the markers, measured in base pairs.

Answer 3

Helking has the description of physical maps correct. But you both are missing a key component of genetic maps. Genetic maps estimate distance between two markers using recombination. Has nothing to do with sequencing, it only sets the "mile markers" for physical mapping. Physical mapping is the act of sequencing and ordering the genome.