4. In the snail Cepaea nemorais, an autosomal allele causing a banded shell (B\"

Question

4. In the snail Cepaea nemorais, an autosomal allele causing a banded shell (B") is recessive to the allele for unbanded shell (BO). Genes at a different locus determine the background color of the shell; yellow (CO is recessive to brown (09). A banded, yellow snail is crossed with a homozygous brown, unbanded snail. The F1 are crossed with a banded, yellow snail (a testcross). a. What will be the results of the tescross if the loci assort independently? 0.5 pts b. What will be the results of the testcross if the loci are linked with no crossing over? 0.5 pts c. What will be the phenotypic results of the testcross if the loci are linked and 20 map units apart? Be sure to include pèrcentages of each phenotype expected. 1 pt

Explanation / Answer

a. One banded brown , one banded yellow , one unbanded(heterozygous) brown and one unbanded(heterozygous) yellow.

b. Unbanded(heterozygous) brown and banded yellow.

c. Percentage of each phenotype is 25% which is expected as from phenotypes explained in (a). But if the map distance in 20 m.u and they are linked so from the formula we know co% = map distance. So it will be 20%.

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