Exam 2: Linkage and Recombination Flashcards
Principle of segregation
Alleles of the same gene separate during meiosis
Principle of independent assortment
Alleles at one locus sort independently from alleles at another locus
Recombination
Alleles sorting into new combinations
Linkage
Refers to the condition in which two genes on the same chromosome tend to be inherited together instead of sorted independently
Explain how linkage affects the outcome of crosses
The results will NOT show a 9:3:3:1 ratio
When genes are linked together, they tend to be assorted into “parental” or “non-crossover” gametes
What does a linkage test cross where half the progeny are parental and half are recombinant reveal?
Independent assortment
True or false: Crossing over cannot occur between linked genes
FALSE
Crossing over can occur, it’s just much less common. The parent gametes will have the highest frequency.
For single crossovers, the frequency of the recombinant gametes is half the frequency of the crossing over because
Each crossover takes place between only two of the four chromatids of the homologous pair
Recombination frequency
Recombinant/Total Progeny
Coupling/cis configuration
One chromosome contains both wild-type alleles, one contains both mutant
Repulsion/trans configuration
Wild-type and mutant allele found on same chromosome
Relate linkage to the chromosomal position of genes and the frequency of crossing over between them
As recombination frequency increases, distance between the genes and the frequency of crossing over increases
Explain how linkage affects the outcome of crosses
The closer two genes are, the more tightly linked they are, and the less likely they are to segregate independently during gamete formation. When two genes are tightly linked, they are more likely to be inherited together, leading to fewer recombinant gametes and a higher frequency of the parental phenotype in offspring.
Contrast parental and recombinant gamete genotypes
Parental gametes have the same genetic combinations as the parents. Recombinant gametes have genetic combinations that differ from those found in either of the parental chromosomes.
Sex-linked vs sex-limited
Sex-linked traits are determined by genes located on the sex chromosomes. Sex-limited traits are determined by genes located on autosomes and express only in one sex.
