A crossed between AB/ab and ab/ab produced 1000 progeny with the following combination. Map the distance between the two genes.
AB ab 368
ab ab 346
Ab ab 142
aB ab 142
Answers
Answer:
A plant of genotype
Image ch5fb18.jpg
is testcrossed to
Image ch5fb19.jpg
If the two loci are 10 m.u. apart, what proportion of progeny will be A B/a b?
45 percent of the progeny will be A B/a b
2. The A locus and the D locus are so tightly linked that no recombination is ever observed between them. If A d/A d is crossed to a D/a D, and the F1 is intercrossed, what phenotypes will be seen in the F2 and in what proportions?
P A d/A d × a D/a D
F1 A d/a D
F2 1 A d/A d
2 A d/a D
1 a D/a D
3. The R and S loci are 35 m.u. apart. If a plant of genotype
Image ch5fb20.jpg
is selfed, what progeny phenotypes will be seen and in what proportions?
4. The cross E/E · F/F × e/e · f/f is made, and the F1 is then backcrossed to the recessive parent. The progeny genotypes are inferred from the phenotypes. The progeny genotypes, written as the gametic contributions of the heterozygous parent, are in the following proportions:
Image ch5fb21.jpg
Explain these results.
The two genes are 33.3 map units (m.u.) apart.
5. A strain of Neurospora with the genotype H · I is crossed with a strain with the genotype h · i. Half the progeny are H · I, and half are h · i. Explain how this is possible.
Because only parental types were recovered, the two genes must be quite close to each other, making recombination quite rare.
Explanation: