Top6-Ch7-P168-202End Flashcards
Crossing over between linked genes produces nonrecombinant and recombinant offspring. See example in answers of a diagram.
Explain coupling and repulsion configuration and how they differ. Also what is another name for both configurations.
Coupling (or cis) configuration is an arrangement where wild type alleles are found on one chromosome and mutant alleles are found on the other chromosome.
Repulsion (or trans) configuration is when each chromosome contains one wild type and one mutant allele.
Recombination is?
the sorting of alleles into new combinations
Interchromosomal recombination is?
sorting of alleles on different chromosomes (independent assortment) or random segregation of chromosomes in anaphas I of meiosis and is the kind of recombination that Mendel discovered while studying dihybrid crosses.
Produces 50% nonrecombinant gametes and 50% recombinant gametes.
Intrachromosomal recombination is?
the sorting of alleles on the same chromosome (crossing over), the exchange of genetic material in prophase I of meiosis.
Often produces less than 50% recombinant gametes, however, if genes are far apart on same chromosome then intrachromosomal recombination also produces 50% recombinant gametes.
Physical evidence of recombination as presented by Creighton and McClintock in 1931.
The recombination frequency is?
determining the proportions of the types of offspring.
What is a three point testcross?
a testcross for three genes
Three types of crossover can take place among three linked loci
- Recombination provides the order of genes and _____ distances
- double cross overs will ____ be counted and underestimate distances
- relative
- not
Recombination between _____ genes can be used for gene ______
different, mapping
To determine the gene order you do what first then what second?
First, determine order of loci
Then, determine cross overs
To map genes what is needed? What is an efficient way to obtain this information?
information abou the location and number of crossovers in the gametes that produced the progeny of a cross is needed.
An efficient way to obtain this information is to use a three point cross test in which an individual heterozygous at three linked loci is crossed with an individual that is homozygous recessive at the three loci.
Recombination between different genes can be used for gene mapping but it ________ frequencies
underestimates
Gene mapping in humans uses? Give an example.
pedigree analysis
Example: linkage of nail-patella syndrome and ABO blood group system.
nail-patella syndrome is a rare autosomal dominant disorder characterised by abnormal fingernails and absent or rudimentary kneecaps.
What is genome wide association
looks at traits in combination with suites of alleles, or looking for nonrandom associations between the presence of a trait and alleles at many different loci scattered across the genome.
It looks for associations between traits and particular suites of alleles in a population.
For instance (see below) a gene involved with bipolar diseases is linked to a certain haplotype.
Crossing over reduces this link
Fast reduction means not close together
What is deletion mapping?
absence of one or more of the bands that are normally on a chromosome reveals a chromosome deletion, a mutation in which part of the chromosome is missing. Genes can be assigned to regions of chromosomes by studying the association between a gene’s phenotype or product and particular chromosomal deletions.
Explain somatic cell hybridization
is the fusion of different types of cells. to do this cells that will divide indefinitely are used (from tumours or altered by viruses) and are cultured in laboratory to create a cell line.
Human and mouse cell lines can fuse to create cells with two nuclei which is called a heterokaryon. The two nuclei gradually fuse then as cell divides then all but a few human chromosomes are lost. The presence of extra human chromosomes in the mouse genome makes it possible to assign human genes to specific chromosomes.
Genes can be localised to a specific part of a chromosome by using somatic-cell hydrisation. See diagram on next page.
In cell line 1 the gene product is present when chromosome 4 is intact.
The gene product is absent in cell line 2 when the entire chromosome 4 is absent.
The gene product is absent in cell line 3 when the short arm is missing.
What is in situ hybridization?
where researchers actually see genes through a radioactive probe that fluoresces under ultraviolet light so that it can be visualised.
