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3.3 Inheritance

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Question 12

In a species of snail, allele B B\,B for a banded shell is dominant to allele b b\,b for an unbanded shell.

Two snails with banded shells are crossed. Two scientists propose different genotypes for the parent snails.

Proposed crossGenotypes of parent snails
1Bb×BbBb \times BbBb×Bb
2BB×BbBB \times BbBB×Bb

The offspring are recorded.

Offspring phenotypeNumber of offspring
Banded shell58
Unbanded shell22
a.

Calculate the percentage of the offspring that have unbanded shells.

[2]
b.

Evaluate which proposed cross is better supported by the offspring results.

[3]
Markscheme

3.3 Inheritance Questions

  1. GCSE
  2. /Biology
  3. /3.3 Inheritance

71 exam-style questions on Edexcel GCSE Biology 3.3 Inheritance, covering 3.3.1 Gregor Mendel and the basis of genetics, 3.3.2 Alleles and inherited characteristics, 3.3.3 Monohybrid inheritance, 3.3.4 Determination of sex at fertilisation, 3.3.5 Outcomes from monohybrid crosses, 3.3.6 Inheritance of ABO blood groups, 3.3.7 Inheritance of sex-linked disorders, and 3.3.8 Multiple genes and phenotypic features. Each one has a worked solution and a mark scheme showing where the marks go.

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