After your great-grandfather Jack passes away, you inherit a bag of seed and an
ID: 8273 • Letter: A
Question
After your great-grandfather Jack passes away, you inherit a bag of seed and an old book, the pages of whichseem to hint of shockingly large plants. You sprout the seed to obtain pure-breeding crops of (1) fast-growing
vines with weak stalks, and (2) slow-growing vines with strong stalks.
a) You cross the two pure-breeding vines but are disappointed to obtain only slow-growing plants with weak
stalks. You then self-cross the F1 vines a number of times, but obtain only the F0 or F1 phenotypes, never the
fast-growing, strong plants that you are hoping for.
Are the genes that control stalk strength and growth rate on the same or separate chromosomes? Write
down the dominant and recessive alleles and give the genotype(s) of the F1 vines. If the genes are on the same
chromosome, indicate which alleles are paired with one another:
Explanation / Answer
Let's start by naming the vine alleles: Fast-growing vines=f slow-growing vines=F weak stalks= S strong stalks = s Based on the set-up of this question, I am assuming dominance in slow-growing vines and weak stalks. Your F0 purebreeding lines were fast-growing vines with weak stalks ffSS and slow-growing vines with strong stalks FFss. F0: ffSS x FFss then F1 would be FfSs (slow-growing vines with weak stalks.) You could fiddle with different combinations of dominance, but this is the only one that would result with an F1 of slow-growing vines with weak stalks. So now, when F1 x F1, the results are only ffSS, FFss, or FfSs. If the growth rate and strength of the plant were not on the same chromosome, then you should see four results, including the fast-growing strong stalk. Because we don't, the two genes are linked (on the same chromosome.). To see this, when crossing F1xF1, the gametes that F1 FfSs will produce are Fs and fS (the parentals). You can plus this into a punnett square, and all you will get are 1/4 ffSS 1/2 FfSs and 1/4 FFss. Therefore, your genes that control stalk strength and growth rate are on the same chromostome, slow-growing and weak stalk are dominant, while fast-growing strong stalk are recessive, and slow-growing strong stalk are paired on the same chromosome (while fast growing weak stalk are paired on their own chromosome together.)