Question

In the snail Cepaea nemoralis, an autosomal allele causing a banded shell (B ) is recessive to the allele for unbanded shell (O ). Genes at a different locus determine the background color of the shell; here, yellow (Y ) is recessive to brown (Bw ). A banded, yellow snail is crossed with a homozygous brown, unbanded snail. The F1 are then crossed with banded, yellow snails (a testcross). What will be the phenotypic classes resulting from a testcross if the loci that control banding and color are linked with no crossing over?

Answer 1

Given: In the Snail Cepded memoralis , - o Banded shell (B) lis recessive to the allele for unbanded shell (0). Yellow colour (Y) is recessive to the allele for Brown colour (Bw). A Banded, yellow snail is crossed with Homozygous brown, unbanded snail: Parents: Parent 1 (Pe) Parent 2 (P2) Homozygous brown, Unbonded snail x Yellgußunded Snail (Bw Bwoo) (YYBB) Bw Bw Y Y UTI * 0 B Bwolny f1 generation: o B Hybrid, Brown, unbanded snail (BwY.OB) Fu generation is test crossed with Banded , Yellow Isnail. je Hybrid Brown, unbanded spail (Bur YOB) is test crossed with Banded, Yellow snail (YYBB)

Es generation (BWYOB) Yellow, banded snail (YY BB) y 4 Bw. Y EB IB Bw 보 B olnud -Crossover Crossover Non-cres Y Buy Y Bw Grametes: Ë B B AB Bw Y Y X Be Y Y Y B B B BO Browon Yellow Brown, Yellow, unbanded banded banded unbanded Isnail snail Snail snail Phenotypes resulting from t'estaross it the loci that control bunding & colour are linked with no-cross Cine Parental combination Phenotypes resulting from testcross if the lock that contool banding & colour are linked with Cross-over. (ie Recombination) over.

Following and colour Answers phenotypes resulting from testcross if the low that control bandi are linked with no - cross over Brown , unbanded sodil Yellow, banded Sndil. je, All snails will be either Brown, unbanded or Yellow, banded. (Ratio : 1:1) +