OpenStax Biology 2e Instructor Answer Guide
Biology 2e
Unit 3: Genetics
Chapter 12: Mendel’s Experiments and Heredity
Visual Connection Questions
1. In pea plants, round peas (R) are dominant to wrinkled peas (r). You do a test cross between
a pea plant with wrinkled peas (genotype rr) and a plant of unknown genotype that has round
peas. You end up with three plants, all which have round peas. From this data, can you tell if
the round pea parent plant is homozygous dominant or heterozygous? If the round pea parent
plant is heterozygous, what is the probability that a random sample of 3 progeny peas will all be
round?
You cannot be sure if the plant is homozygous or heterozygous as the data set is too small: by
random chance, all three plants might have acquired only the dominant gene even if the
recessive one is present. If the round pea parent is heterozygous, there is a one-eighth
probability that a random sample of three progeny peas will all be round.
2. What are the genotypes of the individuals labeled 1, 2 and 3?
Individual 1 has the genotype aa. Individual 2 has the genotype Aa. Individual 3 has the
genotype Aa.
, OpenStax Biology 2e Instructor Answer Guide
3. What ratio of offspring would result from a cross between a white-eyed male and a female
that is heterozygous for red eye color?
Half of the female offspring would be heterozygous (XWXw) with red eyes, and half would be
homozygous recessive (XwXw) with white eyes. Half of the male offspring would be hemizygous
dominant (XWY) withe red yes, and half would be hemizygous recessive (X wY) with white eyes.
4. Figure 12.16 In pea plants, purple flowers (P) are dominant to white flowers (p) and yellow
peas (Y) are dominant to green peas (y). What are the possible genotypes and phenotypes for a
cross between PpYY and ppYy pea plants? How many squares do you need to do a Punnett
square analysis of this cross?
The possible genotypes are PpYY, PpYy, ppYY, and ppYy. The former two genotypes would result
in plants with purple flowers and yellow peas, while the latter two genotypes would result in
Biology 2e
Unit 3: Genetics
Chapter 12: Mendel’s Experiments and Heredity
Visual Connection Questions
1. In pea plants, round peas (R) are dominant to wrinkled peas (r). You do a test cross between
a pea plant with wrinkled peas (genotype rr) and a plant of unknown genotype that has round
peas. You end up with three plants, all which have round peas. From this data, can you tell if
the round pea parent plant is homozygous dominant or heterozygous? If the round pea parent
plant is heterozygous, what is the probability that a random sample of 3 progeny peas will all be
round?
You cannot be sure if the plant is homozygous or heterozygous as the data set is too small: by
random chance, all three plants might have acquired only the dominant gene even if the
recessive one is present. If the round pea parent is heterozygous, there is a one-eighth
probability that a random sample of three progeny peas will all be round.
2. What are the genotypes of the individuals labeled 1, 2 and 3?
Individual 1 has the genotype aa. Individual 2 has the genotype Aa. Individual 3 has the
genotype Aa.
, OpenStax Biology 2e Instructor Answer Guide
3. What ratio of offspring would result from a cross between a white-eyed male and a female
that is heterozygous for red eye color?
Half of the female offspring would be heterozygous (XWXw) with red eyes, and half would be
homozygous recessive (XwXw) with white eyes. Half of the male offspring would be hemizygous
dominant (XWY) withe red yes, and half would be hemizygous recessive (X wY) with white eyes.
4. Figure 12.16 In pea plants, purple flowers (P) are dominant to white flowers (p) and yellow
peas (Y) are dominant to green peas (y). What are the possible genotypes and phenotypes for a
cross between PpYY and ppYy pea plants? How many squares do you need to do a Punnett
square analysis of this cross?
The possible genotypes are PpYY, PpYy, ppYY, and ppYy. The former two genotypes would result
in plants with purple flowers and yellow peas, while the latter two genotypes would result in
