10. In the snail Cepaea nemoralis, an autosomal allele causing a banded shell (B
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Question
10. In the snail Cepaea nemoralis, an autosomal allele causing a banded shell (B") is recessive to the allele for an un-banded shell (B°). Genes at a different locus determine the background color of the shell; yellow (C") is recessive to brown (C). A banded, yellow snail is crossed with a homozygous brown, un-banded snail. The F, are then crossed with banded, yellow snails (a testcross). a. What will the results of the testcross be if the loci that control banding and color are linked with no crossing over?Explanation / Answer
Two loci are linked with no crossing over:
Banded, yellow snail * Homozygous unbanded, brown snail
BB BB CY CY * B0 B0 CBW CBW
B0 CBW
BB CY
B0 BB CBW CY
F1: B0 BB CBW CY
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a.)
Two loci are linked with no crossing over:
F1 (B0 BB CBW CY) * Testcross (BB BB CY CY)
BB CY
B0 CBW
B0 BB CBW CY
BB Cy
BB BB CY CY
B0 BB CBW CY - Unbanded, Brown.
BB BB CY CY - Banded, Yellow.
B0 CBW
BB CY
B0 BB CBW CY
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