Ch. 14 Genetics Practice Problems
I.
Simply Monohybrid Crosses: R = red; r = white
A. Give the genotypic and phenotypic ratios of the offspring from a heterozygous organism crossed with
1. A homozygous dominant organism
2. A heterozygous organism
3. A homozygous recessive organism
B. Do the same crosses as “A” but
1. Have the trait be co-dominant
2. Have the trait be incompletely dominant
II.
Dihybrid Crosses: R = red; r = white; T = Tall; t = short
A. Give the genotypic and phenotypic ratios of the offspring from a doubly heterozygous organism crossed with
1. A doubly heterozygous organism
2. A doubly homozygous recessive organism
B. Do the same crosses as “A” but have both traits be incompletely dominant
III. Beyond Dihybrid Crosses
A. For a AaBbCcDdEe x AaBbCcDdEe cross
1. How many different gametes can each individual produce? How big of a Punnett Square is required for this cross?
2. What are the probabilities of the following offspring from the cross?
a. AaBbCcDdEe
d. 1 Offspring with all dominant traits
b. AABBCCDDEE
e. 1 Offspring R-D-R-D-R traits
c. aaBBccDDee
f. 1 Offspring that have at least one dominant trait
IV. Mulitple Alleles: Blood type
A. What are the offspring phenotypic ratios of
1. An IAio x IBio cross?
B. Combining with dihybrid cross: R+ = “+”; r- = “-“
1. What are the offspring ratios of the following crosses
a. IAIBR+r- x ioioR+rb. IAioR+R+ x IAior-rV.
Epistasis: C = color; c = albino; B = black; b = brown
A. What are the offspring phenotypic ratios for the following crosses
1. Two doubly heterozygous organisms
2. A doubly homozygous dominant organism crossed with a doubly homozygous recessive individual
3. A CCbb x ccBB
VI. Create a Predigree for each of the following before solving for the probability
A. A man who is a carrier for cystic fibrosis marries a woman with a brother with the disorder. Neither of their parents have
the disorder.
1. What is the probability of them having
a. A normal child
b. A child with the disorder
c. A daughter with the disorder
d. Two sons without the disorder
B. A man who is polydactyl has a brother who isn’t and his wife is normal but has a brother who is polydactyl and both of
their parents are polydactyl.
1. What is the probability of them having
a. A normal child
b. A child that is polydactyl
c. Two normal children in a row
d. Two normal children of the same sex in a row
I.
Simply Monohybrid Crosses: R = red; r = white
A. Give the genotypic and phenotypic ratios of the offspring from a heterozygous organism crossed with
1. Genotypic Ratio – 1RR:1Rr ; Phenotypic Ratio – 100% Red
2. Genotypic Ratio – 1RR:2Rr: 1rr; Phenotypic Ratio – 3Red:1White
3. Genotypic Ratio – 1Rr:1rr; Phenotypic Ratio – 1 Red:1White
B. Do the same crosses as “A” but
1. Phenotypic Ratio – 1Red:1Red-White; Phenotypic Ratio – 1 Red:2 Red-White:1White;
Phenotypic Ratio – 1Red-White:1White
2. Phenotypic Ratio: same as above but instead of “Red-White” the phenotype will be pink
II.
Dihybrid Crosses: R = red; r = white; T = Tall; t = short
A. Give the genotypic and phenotypic ratios of the offspring from a doubly heterozygous organism crossed with
1. Genotypic Ratio – 1RRTT:2RRTt:1RRtt:2RrTT:4RrTt:2Rrtt:1rrTT:2rrTt:1tt
Phenotypic Ratio – 9Red-Tall:3Red-Short:3White-Tall:1White-Short
2. Genotypic Ratio – 25% RrTt; 25%Rrtt: 25%rrTt; 25%rrtt
B. Phenotypic Ratio: 1:2:1:2:4:2:1:2:1 for both genotypic and phenotypic ratios
III. Beyond Dihybrid Crosses
A. For a AaBbCcDdEe x AaBBCcDDEe cross
1. AaBbCcDdEe = 25 = 32; AaBbCcDdEe = 25 = 32; Punnett Square = 32 x 32 = a lot = 32 2
2. What are the probabilities of the following offspring from the cross?
a. 1/32
d. 243/1024
b. 1/1024
e. 9/1024
c. 1/1024
f. 1023/1024
IV. Mulitple Alleles: Blood type
A. What are the offspring phenotypic ratios of
1. 1AB:1B:1A:1O
B. Combining with dihybrid cross: R+ = “+”; r- = “-“
1. What are the offspring ratios of the following crosses
a. 3A+:1A-:3B+:1Bb. 3A+:1O+
V.
Epistasis: C = color; c = albino; B = black; b = brown
A. What are the offspring phenotypic ratios for the following crosses
1. 9 Black: 3 Brown: 4 Albinos
2. 100% Black
3. 100% Black
VI. Create a Predigree for each of the following before solving for the probability
A. A man who is a carrier for cystic fibrosis marries a woman with a brother with the disorder. Neither of their parents have
the disorder.
1. What is the probability of them having
a. 5/6
b. 1/6
c. 1/12
d. 25/144
B. A man who is polydactyl has a brother who isn’t and his wife is normal but has a brother who is polydactyl and both of
their parents are polydactyl.
1. What is the probability of them having
a. 1/3
b. 2/3
c. 1/9
d. 1/18