A laboratory population of beetles has either shiny or dull wing cases.
This characteristic is controlled by one gene with two alleles.
The table shows the results of two crosses.
| Cross | Appearance of parents | Shiny offspring | Dull offspring |
|---|---|---|---|
| P | shiny × shiny | 152 | 48 |
| Q | shiny × dull | 97 | 103 |
Explain which appearance is controlled by the dominant allele.
The dominant allele is represented by S S\,S and the recessive allele by sss.
Give the genotype of each parent in cross Q.
A further cross is made between two beetles with the same genotypes as the parents in cross P.
This cross produces 360 offspring.
Calculate the expected number of offspring with dull wing cases.
The cross in part (c) actually produces 82 offspring with dull wing cases.
A student predicts that a repeat of the cross in part (c), using parents with the same genotypes and producing 360 offspring, will produce 98 offspring with dull wing cases. This would give an overall ratio of three shiny offspring to one dull offspring across the two crosses.
Explain why this prediction is not valid.
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.