1. In the snail Cepoea nemoralis, an autosomal allle causing a banded shell (B1)
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Question
1. In the snail Cepoea nemoralis, an autosomal allle causing a banded shell (B1) is recessive to the allele for an unbanded shell (09). Genes at a different locus determine the background color of the shell here, yellow (C) is recessive to brown (C A banded, yellow snall is crossed with a homo crossed with banded, yellow snails xygous brown, unbanded al. The F, are then a. Write out the above cross using appropriate annotation. b. What will the results of the cross be if the loci that control banding and color are linked with no crossing over? Be specific regarding genotypes, phenotypes, and proportions c. What will the results of the cross be f the loci assort independently? Be specific reparding genotypes, phenotypes, and proportionsExplanation / Answer
A) Banded yellow snail has the genotype BBBB CYCY and it produces one type of Gametes BBCY
Homozygous unbanded brown snails have the genotye BOBO CBwCBw and produces gametes BOCBw
Therefoere the F1 generation has the genotype BOBB CBwCY
If F1 is crosse with Homozygous banded yellow snails have the genotye BBBB CYCY, then
BOBB CBwCY X. BBBB CYCY
will give us four different genotypes
-BOBBCBwCY (unbanded brown)
-BOBBCYCY (unbanded yellow)
-BB BBCBwCY (banded Brown)
-BB BBCYCY (Banded yellow)
B) if genes for banding and color are linked, then they are inherited together. Therefore along with allele for banding BB, allele for yellowCY is inherited and similarly allele for no bands BO and allele for brown color CBw is inherited.
Hence during gamete formation for unbanded brown snails with the genotye BOBB CBwCY
, we get 2 gametes BOCBw and BB CY
and for banded yellow snails with the genotye BBBB CYCY, the gamete formed is BB CY
therefore on crossing, we get 2 genotypes
- BOBB CBwCY (phenotype: Unbanded brown, 50% probability)
- BBBB CYCY (phenotype: banded yellow, 50% probability)?
C) If the genes are not linked, then
gamete formed for genotype BOBB CBwCY are BOCBw, BOCY,BB CBw and BB CY
and for banded yellow snails with the genotye BBBB CYCY, the gamete formed is BB CY
therefore on crossing, we get 4 genotypes?
-BOBB CBwCY ((phenotype: unbanded Brown, 25% probability?)?
-BOBB CYCY(phenotype: unbanded Yellow, 25% probability??)??
-BBBB CBwCY(phenotype: banded Brown, 25% probability??)??
-BBBB CYCY(phenotype: banded Yellow?, 25% probability?)??
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