Chromosome Mapping in Eukaryotes Flashcards
Genes assort ______ if they are on different chromosomes but show ______ if they are on the same chromosome.
independently, linkage
In complete linkage, only ______ (______) gametes are produced.
parental, noncrossover
If crossing over between two ______ occurs between two ______, both ______ and ______ (______) gametes are produced.
linked genes, nonsister chromatids, parental, recombinant, crossover
If complete linkage exists between two genes because of their close ______ and organisms ______ at both ______ are mated, a unique F2 ______ ratio designated the ______ results.
proximity, heterozygous, loci, phenotypic, linkage ratio
Genes on the same chromosome are part of a ______.
linkage group
The number of linkage groups should correspond to the ______ number of ______.
haploid, chromosomes
The percentage of offspring resulting from ______ gametes depends on the ______ between the two ______ on the chromosome.
recombinant, distance, genes
Synapsed chromosomes in meiosis wrap around each other to create ______ that are points of genetic exchange.
chiasmata
Two genes located relatively close to each other along a chromosome are less likely to have a ______ form between them, and it is less likely that ______ will occur.
chiasma, crossing over
The recombination frequencies between linked genes are ______, and the ______ is an estimate of the relative ______ between two genes along the chromosome.
additive, frequency of exchange, distance
One ______ is defined as 1 percent recombination between two genes on a chromosome.
map unit (mu)
Map units are often called ______ and are ______, not exact ones.
centimorgans (cM), relative distances
A ______ alters linkage between two genes only if the crossover occurs between those two genes.
single crossover (SCO)
______ can be used to determine the distance between two linked genes, but ______ can be used to determine the ______ of three genes on the chromosome and the ______ between the linked genes.
Single crossovers, double crossovers (DCOs), order, distance
To study double exchanges, ______ pairs of genes must be investigated, each ______ for ______ alleles.
three, heterozygous, two
The expected frequency of double-crossover gametes is much ______ than that of either single-crossover gamete class.
lower
In Three-Point Mapping,
• Parent must be ______ for all ______ genes under consideration.
heterozygous, 3
In Three-Point Mapping,
• Cross constructed so genotypes can be determined by ______.
offspring phenotypes
In Three-Point Mapping,
• Many offspring produced to get a ______ of crossover events.
representative sample
The ______ occur in the greatest proportion of offspring.
noncrossover F2 phenotypes
The ______ occur in the smallest proportion.
double-crossover phenotypes
Because the F2 phenotypes complement each other (i.e., one is wild type and the other is mutant for all three genes), they are called ______ of phenotypes.
reciprocal classes
Distance between two genes in a three-point cross is ______ to the percentage of all detectable exchanges occurring between them and includes all single and double crossovers.
equal
2 methods for determining gene order from a three-point cross:
• Method I
• Method II
2 methods for determining gene order from a three-point cross:
______
• Determine arrangement of alleles on homologs of heterozygote producing crossover gametes by identifying reciprocal noncrossover phenotypes
Method I
2 methods for determining gene order from a three-point cross:
______
• test each of 3 possible orders to see which one gives you the observed double-crossover phenotypes – the one that does is the winner!
Method I
2 methods for determining gene order from a three-point cross:
______
• Determine arrangement of alleles on homologs of heterozygote producing crossover gametes by identifying reciprocal noncrossover phenotypes
Method II
2 methods for determining gene order from a three-point cross:
______
• Look at observed double-crossover phenotypes and id single allele that has been switched
- Will be one that is by itself (no longer associated w/other mutant alleles)
- That is the one in the middle!
Method II
Chromosome Mapping is Now Possible Using ______ and ______
DNA Markers, Annotated Computer Databases
______ represent landmarks along the chromosome.
DNA markers
DNA markers represent landmarks along the
chromosome:
• RFLPs – Restriction Fragment Length Polymorphisms
• Microsatellites
• SNPs – Single Nucleotide Polymorphisms
