Two genes 'A' and 'B' are linked. In a dihybrid cross involving these two genes, the F1-heterozygote

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Two genes 'A' and 'B' are linked. In a dihybrid cross involving these two genes, the F1-heterozygote is crossed with homozygous recessive parental type (aa bb). what would be the ratio of offspring in the next generation?

Accepted Answer

Sol.(d) [Key Concept: Linkage — Test Cross with Linked Genes] When two genes A and B are LINKED (on the same chromosome), the F1 heterozygote (AB/ab) crossed with double recessive (ab/ab) — a test cross — produces mainly PARENTAL TYPES: AB/ab (dominant phenotype) and ab/ab (double recessive) in approximately 1:1 ratio. There are very few recombinants (Ab/ab and aB/ab). Since the question asks about the ratio without specifying crossing over frequency, the predominant result with linked genes would be approximately 1:1 (two parental types). Answer: (d) 1:1.

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