Genetics- Key Terms #3

Front 1

ascospore

Back 1

a spore contained in an ascus or that was produces inside an asucs; specific to fungi classified as ascomycetes; typically a single ascus will contain 8 ascospores; a meiotic spore

Front 2

ascus (pl. asci)

Back 2

the sexual spore-bearing cell (sac) produced in ascomycete fungi

Front 3

centimorgan (cM)

Back 3

a unit of distance between genes on chromosomes representing 1% crossing over between two genes; equivalent to 1 map unit (m.u.).(one cM corresponds to about 1 million base pairs in humans on avg)

Front 4

crossover

Back 4

an exchange of genetic material between homologous chromosomes by breakage and reunion; the exchange of material between nonsister chromatids during meiosis is the basis of genetic recombination (online definition: one of the final phases of genetic recombination, which occurs during prophase I of meiosis in a process called synapsis. Usually occurs when matching regions on matching chromosomes break and then reconnect to the other chromosome.)

Front 5

four-strand double crossover

Back 5

a single crossover between two chromatids and then a second single crossover between the remaining chromatids. the result is that all four products are recombinant.

Front 6

genetic map (chromosome map)

Back 6

a diagram showing the location of genes on chromosomes (includes the DNA seq of a gene with introns and exons, 3' or 5' transcribed-untranslated regions, termination signal, regulatory elements such as promoters, enhancers and it may include known mutations defining alternative alleles of the same gene)

Front 7

interference (positive interference)

Back 7

a measure of the degree to which one crossover affects the incidence of another crossover in an adjacent region of the same chromatid (the reduction of the likelihood of another crossover in the vicinity of a nearby crossover); negative interference increases the chance of another crossover; positive interference reduces the possibility of a second crossover event.

Front 8

linkage

Back 8

the tendency of certain loci or alleles to be inherited together; genetic loci that are physically close to one another on the same chromosome tend to stay together during meiosis and are thus genetically linked; occurs as an exception to independent assortment

Front 9

linkage group

Back 9

genes that are inherited as a single unit because they are near one another on the same chromosome. ex: in fruit flies, the genes affecting eye color and wing length are inherited together because they appear on the same chromosome

Front 10

linkage map

Back 10

a genetic map of a species that shows the position of its known genes or genetic markers relative to each other in terms of recombination frequency, rather than as specific physical distance along each chromosome; critical for identifying the location of genes that cause genetic diseases

Front 11

lod score

Back 11

(logarithm (base 10) of odds) is a statistical test to determine whether two loci are linked or unlinked; positive LOD scores favor the presence of linkage, whereas negative LOD scores indicate that linkage is less likely. a LOD score of 4 indicates that linkage is 10,000 times more likely than nonlinkage. by convention, scores of 3-4 are signs of linkage

Front 12

**map distance

Back 12

look up in book

Front 13

mapping function

Back 13

a mathematical formula that relates map distances to recombination frequencies

Front 14

non-parental ditypes (NPD)

Back 14

a spore arrangement in that contains only the two recombinant-type ascospores (assuming two segregating loci). [a tetrad type containing two diff genotypes, both of which are recombinant]

Front 15

parental ditype

Back 15

a tetrad type containing 2 diff genotypes, both of which are parental. A spore arrangement in Ascomycetes that contains only the two-recombinant-type ascospores

Front 16

noncrossover gamete

Back 16

a gamete whose chromosomes have undergone no genetic recombination

Front 17

recombinant frequency (% recombinants)

Back 17

a measure of genetic linkage and is used in the creation of a genetic linkage map; the frequency with which a single chromosomal crossover will take place bw two genes during meiosis; a centimorgan (cM) is a unit that describes a recombination frequency of 1%

Front 18

crossover gamete

Back 18

a gamete whose chromosomes have undergone genetic recombination

Front 19

syntenic genes

Back 19

book definition: in somatic cell genetics, a method for determining whether two genes are on the same chromosome
(internet definition: co-localization of genetic loci on the same chromosome within an individual or species; related to genetic linkage: linkage bw two loci is established by the observation of lower-than-expected recombination frequencies between them. in contrast, any loci on the same chromosome are by definition syntenic, even if their recombination frequency cannot be distinguished rom unlinked loci by practical experiments. Thus, in theory, all linked loci are syntenic, but not all syntenic loci are necessarily linked.)

Front 20

tetrad

Back 20

the 4 chromatids that make up paired homologs in the prophase of the first meiotic division. In eukaryotes with a predominant haploid stage (some algae and fungi) tetrad denotes the 4 haploid cels produced by a single meiotic division.

Front 21

three-strand double crossover

Back 21

results when one chromatid crosses over with two other chromatids. The result is two parental and two recombinant progeny, the same as a single crossover event.

Front 22

two-strand double crossover

Back 22

result of two chiasma between the two loci involving the same two sister chromatids. these two events cancel each other out and result in parental or non-recombinatnt progeny