In the plant Arabidopsis thaliana , a mutant phenotypecalled twisted leaves may
ID: 4829 • Letter: I
Question
In the plant Arabidopsis thaliana, a mutant phenotypecalled twisted leaves may be caused by either a chloroplast gene(CT = normal; Ct = twisted)or a recessive nuclear gene (NT = normal;Nt = twisted). Chloroplasts in these plants arematernally inherited. Predict the genotypic and phenotypic ratiosin the offspring of the following crosses. Note: Normal leavesare dominant. Therefore, even one normal allele is enough to givenormal leaves.
i) CT NtNt female ´ CtNTNT male
ii) Ct NtNt female ´ CTNTNT male
iii) F1 female from cross (i) ´ F1 male from cross (ii)
iv) F1 female from cross (ii) ´ F1 male from cross (i)
Explanation / Answer
CT allele=normal; CT CT= normal CT Ct= normal
Ct = twisted or arecessive nuclear gene
Chloroplasts in these plants are maternallyinherited
NT allele = normal;NT NT = normal;NT Nt =normal;
Nt = twisted.recessive gene
CT NtNtfemale x Ct NTNTmale
Gametes CTNt Ct NT
CT Ct NT Nt ------------- offspring
So CT Ct NT Nt ----------normal
ii) Ct NtNt female x CTNTNT male
Gametes CtNt CT NT
CT Ct NTNt normal
iii) F1 female from cross (i) ´ F1 male from cross (ii)
CTNtNt female x CT NTNT male
Gametes CTNt CT NT
CT Nt CTNT -normal
iv) F1female from cross (ii) ´ F1 male fromcross (i)
Ct NtNtfemale x Ct NTNT male
Gametes --------- CtNt CtNT
Ct Nt CtNT -normal
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