Monohybrid problems and the dihybrid cross
Answers are for parents and teachers.
1
Two parents with the dominant phenotype have a recessive child. Write the parents’ genotypes and find the probability.
Both Aa; the probability of recessive aa is ¼ (25%).
2
In dogs short hair (L) is dominant over long hair (l). A homozygous short-haired female is crossed with a long-haired male. Write the genotypes and phenotypes of F1 and F2.
P: LL × ll; F1 all Ll (short-haired); F2: ¼ LL, ½ Ll, ¼ ll, i.e. 3 short-haired : 1 long-haired.
3
AaBb × AaBb gave 3200 plants. About how many are recessive for both traits (aabb)?
200
4
AaBb × aabb gave 600 offspring. About how many of each phenotype?
150
5
Use a Punnett square to show the phenotype ratio of F2 in AaBb × AaBb.
Of 16 squares, 9 are A_B_, 3 A_bb, 3 aaB_ and 1 aabb: 9:3:3:1.