Heredity (B): two traits, carriers and counselling
Answers are for parents and teachers.
1
List the four gametes of TtGg and give the number of boxes in the Punnett square for TtGg × TtGg.
TG, Tg, tG, tg; 16 boxes.
2
From TtGg × TtGg, what fraction of offspring are short with green pods (tt, G-)?
3/16 (short green-podded).
3
Of 80 offspring from two carriers (Rr × Rr), about how many are expected to be affected, and how many healthy?
25 % of 80 = 20 affected, and 60 healthy.
4
Explain in two sentences why a carrier is healthy.
The carrier has one normal allele, and the disease allele is recessive, so it is hidden. The disease shows only with two disease alleles.
5
Write one respectful sentence that explains what a genetic counsellor does.
A genetic counsellor explains the chances of an inherited disease to a family, using its medical history and test results, so that the family can plan.