Gene mapping 1 Flashcards
(42 cards)
What is the Law of Independent Assortment?
Genes segregate and assort independently during gamete formation.
All gametic combinations (parental and recombinant) appear with equal frequency.
What is the expected ratio of gametic combinations for independent assortment?
AB : ab : Ab : aB :: 1:1:1:1
What occurs when there is no crossing over?
No recombinant gametes; genes cosegregate in parental combinations.
What happens when crossing over occurs?
Both parental and recombinant gametes form, leading to independent assortment.
How does linkage affect genes on a chromosome?
Genes close to each other on a chromosome are less likely to separate by crossing over.
What is a linkage group?
A group of genes that cosegregate; the largest linkage group is a chromosome.
What is observed in a testcross with complete linkage?
Only parental combinations are observed.
What does linkage with crossing over reveal?
More than 50% parental, less than 50% recombinant.
What is recombination frequency proportional to?
The distance between genes.
What characterizes linked genes?
Genes with < 50% recombination are linked, while those with ≈ 50% are unlinked.
What is the coupling configuration?
Dominant alleles on one homolog, recessive on the other (e.g., AB/ab).
What is the repulsion configuration?
Each homolog carries one dominant and one recessive allele (e.g., Ab/aB).
What did Morgan’s experiments with Drosophila demonstrate?
Varying recombination frequencies and linear arrangement of linked genes on chromosomes.
What is a genetic map?
Estimates the order and distance between genes using recombination frequencies.
What is the unit of genetic distance?
Map unit (mu) or centi-Morgans (cM); 1 mu = 1% recombination = 1 crossover in 50 cells.
What is a genetic marker?
Alleles used to trace recombination events.
What are physical maps used for?
Calculate actual distances between genes using molecular methods.
What is a limitation of genetic maps?
Species-specific recombination frequency.
What can cause underestimation of genetic distances?
Multiple crossovers can mask recombinant offspring.
What is the maximum observable recombination frequency?
50%.
What does three-point mapping involve?
Three loci to determine gene order and calculate distances.
What are the criteria for three-point mapping?
- Heterozygous parent at all loci
- Test cross with a homozygous recessive parent
- Sufficient offspring for all crossover classes
