How are cross-over events identified? Consider two flies, a male that is homozygous recessive for the two genes cross-vein wings (cv)and cut wings (ct), so has the genotype cv+ct+/cvct He is crossed to a double heterozygote female with the genotype cv+ct+/cvct Question: Assuming that the genes are unlinked, what will be the phenotypes of the offspring from the cross above?
In general terms, genes found on the same chromosome are linked, and will appear to defy Mendel’s Law of Independent Assortment. This law states that alleles (Links to an external site.) for different traits (Links to an external site.) are transmitted (Links to an external site.) to offspring (Links to an external site.) independently of one another. Functionally, this means that in a dihybrid testcross, in which a heterozygote is crossed to a double homozygous recessive individual, the expected 1:1:1:1 ratio will not be obtained.
Instead, lower than expected numbers of non-parentals will result, because these non-parental flies are the result of recombination during synapsis. Interestingly, and functionally important in this exercise, synapsis only occurs in female fruit flies, requiring that the heterozygote in any study of linkage must be the female.
Determining the relative positions of linked genes on a chromosome can be accomplished by calculating the frequency of crossing-over between two genes of interest. The closer the genes are together, the less frequently crossing-over will occur between them. The probability of crossing-over is expressed as a percentage. Each 1% of crossing-over is also referred to as one map unit (m.u.).
How are cross-over events identified? Consider two flies, a male that is homozygous recessive for the two genes cross-vein wings (cv)and cut wings (ct), so has the genotype cv+ct+/cvct
He is crossed to a double heterozygote female with the genotype cv+ct+/cvct
Question: Assuming that the genes are unlinked, what will be the
Question: If the genes were completely linked (think of them as being at the same spot with no possibility of crossing-over), what phenotypes would you expect? (COMPLETE linkage as described here is not a usual occurrence, but working through this problem helps to visualize the differences)
Trending now
This is a popular solution!
Step by step
Solved in 3 steps
Assuming that the genes are unlinked, what will be the
by Bartleby Expert
