Mapping eakaryote chromosomes by recombination

25 important questions on Mapping eakaryote chromosomes by recombination

The “distance” between two linked gene pairs where 1 percent of the products of meiosis are recombinant; a unit of distance in a linkage map.

Map Unit (m.u.); centiMorgan (cM)

A representation of all chromosomes in the genome as lines, marked with the positions of genes known from their mutant phenotypes, plus molecular markers. Based on analysis of recombinant frequency

Chromosome map

The exchange of corresponding chromosome parts between homologs by breakage and reunion.

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Meiotic product cells with chromosomes that have engaged in a crossover.

Crossover products

The autoradiographic banding pattern produced when DNA is digested with a restriction enzyme that cuts outside a family of VNTRs (variable number of tandem repeats) and a Southern blot of the electrophoretic gel is probed with a VNTR-specific probe. Unlike true fingerprints, these patterns are not unique to each individual organism.

DNA fingerprint

A DNA break cleaving the sugar– phosphate backbones of both strands of the DNA double helix

Double-stranded break

A linear pattern of spore phenotypes within an ascus for a particular allele pair, produced when the alleles go into separate nuclei at the first meiotic division, showing that no crossover has taken place between the allele pair and the centromere.

First-division segregation pattern (M1 pattern)

A distance on the chromosome map corresponding to 1 percent recombinant frequency.

Genetic map unit (m.u.)

DNA in which there is one or more mismatched nucleotide pairs in a gene under study.

Heteroduplex DNA

A chromosome map; an abstract map of chromosomal loci that is based on recombinant frequencies.

Linkage map

The situation in which two genes are on the same chromosome as deduced by recombinant frequencies less than 50 percent.

Linked genes

A formula expressing the relation between distance in a linkage map and recombinant frequency.

Mapping function

A difference in DNA at the same locus in two genomes that is due to different repeat lengths of a microsatellite.

Microsatellite marker

Heterozygous locus representing a variable number of tandem repeats of a unit 15 to 100 nucleotides long.

Minisatellite marker

An ascus containing eight ascospores, produced in species in which the tetrad normally undergoes a postmeiotic mitotic division.

Octad

The ordered and oriented map of cloned DNA fragments on the genome.

Physical map

A mathematical distribution giving the probability of observing various numbers of a particular event in a sample when the mean probability of an event on any one trial is very small.

Poisson distribution

The proportion (or percentage) of recombinant cells or individuals.

Recombination frequency (RF)

A difference in DNA sequence between individuals or haplotypes that is recognized as different restriction fragment lengths. For example, a nucleotide-pair substitution can cause a restrictionenzyme-recognition site to be present in one allele of a gene and absent in another. Consequently, a probe for this DNA region will hybridize to different-sized fragments within restriction digests of DNAs from these two alleles.

Restriction fragment length polymorphism (RFLP)

A pattern of ascospore genotypes for a gene pair showing that the two alleles separate into different nuclei only at the second meiotic division, as a result of a crossover between that gene pair and its centromere; can be detected only in a linear ascus.

Second-devision segregation pattern (MII)

The existence in the population of individuals showing different numbers of copies of a short simple DNA sequence at one chromosomal locus.

Single-sequence length polymorphism (SSLP)

A nucleotidepair difference at a given location in the genomes of two or more naturally occurring individuals.

Single nucleotide polymorphism (SNP)(snip)

A testcross in which one parent has three heterozygous gene pairs.

Three-point testcross (three-factor testcross)

In a heterozygote with two mutant sites within a gene or gene cluster, the arrangement a1 +/+ a2.

Trans conformation

A chromosomal locus at which a particular repetitive sequence is present in different numbers in different individuals or in the two different homologs in one diploid individual.

Variable number tandem repeat (VNTR)

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