ch 23 genetics

what is an STS?

(sequence tagged site) - a short segment of DNA who's base sequence is found to be unique within an entire genome, in which the sequence is identified by PCR

how does a micro satellite work?

1) add PCR to a set of chromosomes 2) the PCR primers specifically recognize sequences on chronometer 2 that flank a particular micro satellite 3) many cycles of PCR produce a large amount of DNA fragment contained between the two primers. The DNA is subjected to Gell electrophoresis

three general approaches to mapping a chromosome

1) cytogenetic 2) linkage 3) physical mapping

what is the FISH procedure?

1) treat cells with agents that make them swell and fix 2) denature chromosomal DNA 3) add single stranded DNA probes that have biotin incorporated into them 4) add fluorescently labeled avidin that binds to biotin 5) view with fluorescent microscope

what is FISH?

Fluorescently labeled situ hybridization, commonly use in genetics and cell biology research

how does the probe bind in the FISH procedure?

Probe binds to a site in the chromosomes where the gene is located because the probe is subsequently tagged with a fluorescent molecule (due to biotin nucleotides) biotin has a very high affinity for avidin, so when fluorescently labeled avidin is added, tagging occurs due to the tight biding of the biotin and avidin

genetic map/ chromosome map

a diagram that describes relative locations of genes or other DNA segments along a chromosome

how is the fluorescently labeled probe detected?

a fluorescently labeled molecule absorbs light at a particular wavelength and then emits light at a longer wavelength must look at this through a fluorescence microscope

define contig

a series of clones that contain contiguous, overlapping pieces of chromosomal DNA. This represents a physical map of a chromosome

how long is the human genome?

about 3 billion base pairs in length

which of the following is an example of a molecular marker?

all of the above - RFLP, micro satellite, single-nucleotide polymorphism

linkage mapping

analyzing basic spacing and order of genes along a chromosome by analyzing the outcome of crosses

how are cloned DNA fragments characterized in physical mapping?

by their size, length in base pairs, as well as genes they contain and their relative locations along a chromosome

how would FISH be used in a clinical setting?

can detect changes in chromosome structure, such as deletions, duplications, and translocations

how are cells prepped in FISH procedure?

cells are prepped keeping chromosomes intact and treated with agents that cause them to swell - contents are fixed to the slide

chromosome painting

chromosomes hybridized with fluorescent dye to show their origins

23.2 concept check what type of chromosome mapping relies on microscopy?

cryogenic mapping

physical mapping

determining locations of and distances between genes and other sequences on a chromosome using DNA-cloning techniques

cryogenic mapping

determining locations of specific sequences with chromosomes that are viewed microscopically each chromosome of a given species has a specific banding pattern, genes are mapped relative to band location

what is the difference between eukaryotic chromosomes and bacterial chromosomes?

eukaryotic chromosomes can be distinguished from bacterial by their size (euks are larger), centromeric location, and banding patterns

what is the most common method of stu hybridization?

fluorescence in situ hybridization (FISH)

23.2 comprehension question: the technique of a fluorescence in situ hybridization involves the use of a _______ that hybridizes to a ________

fluorescent probe, specific site on an intact chromosome

how can a large number of markers be used?

genetic maps with a large number of markers are used by evolutionary biologists to determine patterns of genetic variation within a species and evolutionary relatedness of different species

polymorphic

having various forms

hybridization

indicates that the labeled strand of DNA base-pairs and thereby forms a hybrid with an intact chromosome

molecular marker

is a segment of DNA found at a specific site along a chromosome with properties that enable it to be uniquely recognized using molecular tools, like PCR and gel electrophoresis

what is a benefit of cryogenic mapping?

it can be used as the first step in the localization of genes in plants and animals

what are the limitations of cryogenic mapping?

it relies on light microscopy, so it is pretty limited resolution and is usually only accurate within limits of approximately 5 million bp along a chromosome. works well with species that have large polytene chromosomes like Drosophilia

situ

latin for "in place" and indicates that the procedure is conducted on chromosomes that are being held in place

how can molecular markers be polymorphic

like alleles, molecular markers can vary from individual to individual within a population, making them polymorphic

to map the distance between molecular markers via testcrosses, the markers must be:

polymorphic

mapping

refers to the experimental process of determining the relative locations of genes or other segments of dna along individual chromosomes

locus

refers to the site within a genetic map where a specific gene or other DNA segment is found

what is a key feature of physical mapping strategy?

researchers must characterize many DNA clones that contain much smaller pieces of the genome

a molecular markers is _____ found at a specific site on a chromosome that has properties that allow it to be _______

segment of DNA, uniquely identifies using molecular tools

what is a micro satellite?

short repetitive sequences interspersed through a species genome and tend to vary in length among different individuals

what is so convenient about molecular markers?

the distances between linked markers can be determined from the outcomes of the crosses, meaning it is easier to identify molecular markers in a genome rather than looking at many allelic differences that affect a trait molecular markers serve as a good point of reference

23.2 concept check: why does the probe bind to a specific site on a chromosome?

the probe binds. to a specific site because that. site has a complementary sequence

what do molecular markers do?

they can be used to determine the approximate location of an unknown gene that causes a human disease

what do cytogeneticists do with band patterns?

they use banding patterns as a way to describe specific regions along the chromosome's length

what is the goal of cryogenic mapping?

to determine the location of a gene on an intact chromosome It can localize a particular gene to a site within a chromosomal banding pattern

when is cryogenic mapping used?

used in genetic studies of eukaryotes, which have large chromosomes compared to bacteria.

What is in situ hybridization?

used to cytogenetically map the locations of genes or other DNA sequences within a large eukaryotic chromosomes

what makes micro satellites polymorphic?

when the number of repeat sequences vary

what is a founder

where the disease causing allele originated many generations ago