Question

ing genetic map: 2. 3 > chromosome 3: 5 N. 35 me chromosome 7: >0 20 mu <a 15E ASR 7 8 9 10 Questions 1-6 are to be answered in order in the respective boxes below. Final answers must be entered online. (Your answer should be a number between 0 and 100 to two decimal places for example, one number as a final answer including or between "0.00" through "100.00"). Round to the nearest hundredths and do not include the percentage sig If your answer is 12.345%, then 12.35 is how you should express this final answer Question 1: What proportion of progeny from a testcross of a cis-dihybrid of gonos and E should be dominant for both characteristics? Question 2: What proportion of progeny from a testcross of a trans-dihybrid of ger N and E should be parentals? Question 3: What proportion of progeny from a testcross of a trans-dihybrid of gen O and F should be recessive for one characteristic but dominant for the other? Question 4: What proportion of progeny from a testcross of a cis-dihybrid of genes and R should be recessive for A and dominant for R? E Question 5: What proportion of progeny from a testcross of a dihybrid of genes and A should be recessive for both characteristics?

Answer 1

Okay, remember that a cys hybrid means that the recessive alleles are in one chromosome and the dominant alleles are in the other one. The trans hybrids are just the opposite, one recessive allele is with one dominant allele in one single chromosome and the other has their complements.

Let us use the example of chromosome 7 in this exercise, a cis hybrid would have a genotype of "A R / a r", while a trans hybrid has the genotype "A r / a R". It is the same genotype but they are arranged differently.

Now, remember that map units are just recombination frequencies, so to know which proportion will have certain combination we only need to use the map units that separate the genes in question. Let us beggin:

1.- F and E are separated by only 15 mu, and the parent is cis hybrid (F E / f e). We want both traits to be dominant so we require for no recombination and to inherit the F E haplotype. That means we require the 85% (100-15 = 85) probability of no recombination, and only half of it will provide the F E (the other half is f e). Then:

85/2 = 42.5

The answer is 42.5%

2.- N and E are separated by 70 mu (35+20+15), and the parent is trans (N e / n E). We want either of the parental haplotypes so that means we require the non recombinant events, the probability of evading recombination here is 30% (100-70= 30), and we don't have to divide by 2 because either of the parental haplotypes is right.

The answer is 30%

3.- O and F are separated by 20 mu, the parent is trans (O f / o F) and we require one dominant and one recessive trait, that means we require to not recombine the alleles (because they are already arranged in the parent as we require them). Then, the probability to avoid recombination is 80 (100-20 = 80).

The answer is 80%

4.- A and R are separated by only 7 mu, the parent is cis (A R / a r) and we require recessive A and dominanr R. This means we require recombination and only one of the 2 haplotypes resulting from this recombination will work (because the other haplotype will be dominant A and recessive R, just the opposite). The recombination frequency is directly the distance so it is 7%, now divide this by 2:

7/2 = 3.5

The answer is 3.5%

5.- Now the gae changes because both parents are hybrid (in the previous questions only one was hybrid and the other one was recessive homozygous). Also in this case we are going to ignore linkage since A and E are in different chromosomes, we only need to do a Punnet square:

	A E	A e	a E	a e
A E	AA EE	AA Ee	Aa EE	Aa Ee
A e	AA Ee	AA ee	Aa Ee	Aa ee
a E	Aa EE	Aa Ee	aa EE	aa Ee
a e	Aa Ee	Aa ee	aa Ee	aa ee

Note that only 1 out of 16 is homozygous recessive for both traits, that is:

(1/16)(100) = 6.25%

The answer is only the 6.25%