The exercise
Six questions covering the chapter. Work each one on paper before looking anything up — most of them are a Punnett square and a careful reading of what is being asked.
1. Inherited or not
For each of the following, state whether it is an inherited characteristic or one acquired during a lifetime, and give your reason: the ability to roll the tongue; a scar on the arm; attached ear lobes; the muscle built up by a year of training; albinism.
2. Genotypes in the F2
A pure-breeding pea plant with genotype BB is crossed with one of genotype bb. The F1 plants are then allowed to cross among themselves.
- Draw the Punnett square for the F1 cross.
- What percentage of the F2 generation has the same genotype as one of the original parents?
3. Two words
Explain the difference between genotype and phenotype, using stem height in the pea plant as your example. Why can two plants with different genotypes have the same phenotype?
4. Sex determination
Draw the cross that determines the sex of a human child. Use it to explain why the father, and not the mother, determines the sex, and why the chance of a son is one in two at every conception regardless of the children already born.
5. A test cross
In the pea plant, green pod colour (G) is dominant over yellow (g). A green-podded plant is found, but it is not known whether it is GG or Gg.
- Which plant should it be crossed with to find out, and why that one?
- What result would show that it is Gg, and what result would show that it is GG?
6. Weighing an application
Which of the following is a possible harmful consequence of genetic engineering? (i) Insulin can be produced in large quantities for people with diabetes. (ii) Human beings could be modified to order, for characteristics their parents prefer. (iii) Crops can be given resistance to a disease that ordinary breeding cannot supply. (iv) Vaccines can be made without handling live virus.
Three questions have been corrected
The printed exercise contains three faults. Each is fixed above, and the change is recorded so that a reader working from the textbook can see what differs and why.
- Question 2 as printed asks for the percentage of the F1 showing a parental genotype. Every F1 plant is Bb, so the answer is 0 per cent, which is not among the printed options. Asking about the F2 gives 50 per cent, which is the printed answer.
- Question 5 as printed writes g for both the dominant green and the recessive yellow, so the cross cannot be written down at all. The dominant allele is given as G above.
- Question 6 as printed offers two defensible answers. One of them has been replaced with a clearly beneficial statement, so that only option (ii) stands.