Home / AP Biology : 5.3 Mendelian Genetics – Exam Style questions with Answer- MCQ

AP Biology : 5.3 Mendelian Genetics – Exam Style questions with Answer- MCQ

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Question

Researchers performed a dihybrid cross with coffee bean plants to investigate whether the inheritance of two traits (height and stem circumference) follows Mendel’s law of independent assortment. The data for the \(F_2\) generation are presented in Table 1.

Which of the following is closest to the calculated chi-square (\(χ^2\)) value for the data presented in Table 1?

A. 8.35
B. 72.01
C. 98.00
D. 2,546.00

▶️Answer/Explanation

Ans: B
Correct. 72.01 is the correct calculated answer using the formula\(X^2 = \Sum \frac{(o-e)^2}{e}\).

Question

Researchers hypothesized that red eye color in Japanese koi, a type of fish, is due to a mutation. To study the inheritance of red eye color in koi, the researchers conducted breeding experiments over several generations. The results are summarized in Figure 1.

The figure presents a pedigree with three generations of Japanese koi. In the first generation, a black-eyed male and a red-eyed female have the following three offspring as part of the second generation: a red-eyed female, a red-eyed male, and a red-eyed female. The second generation red-eyed female has the following two offspring with a red-eyed male: two black-eyed females. The second generation red-eyed male has the following two offspring with a black-eyed female: a red-eyed female and a red-eyed male. The second generation red-eyed female has the following two offspring with a black-eyed male: a red-eyed male and a black-eyed male.

Figure 1. Inheritance of eye color in Japanese koi

Based on the data in Figure 1, which of the following is the best prediction of the mode of inheritance of red eyes in Japanese koi?

A. The allele for red eyes is inherited in an autosomal dominant pattern.

B. The allele for red eyes is inherited in an autosomal recessive pattern.

C. The allele for red eyes is inherited in an X-linked recessive pattern.

D. The allele for red eyes is inherited in an X-linked dominant pattern.

▶️Answer/Explanation

Ans: A
Based on the pedigree, red eye color in koi is inherited in an autosomal dominant pattern. In the second generation, two koi with red eyes produced female offspring with black eyes. This could only happen if the parents were heterozygous with the dominant allele.

Question

In corn plants, purple kernel color is dominant to yellow kernel color, and smooth kernels are dominant to wrinkled kernels. Researchers carried out a genetics experiment to investigate whether the genes controlling kernel color and kernel texture segregate independently. In their experiment, the researchers crossed two corn plants that were each heterozygous for both kernel color and kernel texture. The results of the experiment are presented in Table 1.

Using a significance level of p=0.05, which of the following statements best completes a chi-square goodness-of-fit test for a model of independent assortment?

A. The calculated chi-square value is 0.66, and the critical value is 0.05. The null hypothesis can be rejected.
B. The calculated chi-square value is 0.66, and the critical value is 3.84. The null hypothesis cannot be rejected.
C. The calculated chi-square value is 3.91, and the critical value is 5.99. The null hypothesis can be rejected.
D. The calculated chi-square value is 3.91, and the critical value is 7.82. The null hypothesis cannot be rejected.

▶️Answer/Explanation

Ans: D
Because the null hypothesis is based on a model of independent assortment, the phenotypic ratios are expected to be 9:3:3:1. Using the equation \(x^2 = \Sum \frac{(o-e)^2}{e}\). the calculated chi-square value is 3.91. With three degrees of freedom (one less than the number of phenotypic categories) and a significance level of p=0.05, the critical value is 7.82. Because the calculated chi-square value is less than the critical value, the null hypothesis cannot be rejected. In other words, the data collected in the genetics experiment fit a model of independent assortment.

Question

Several members of a family are found to involuntarily sneeze when exposed to bright lights, such as sunlight. Following analysis of the condition in the family, a doctor predicts that the symptoms have an underlying genetic basis. A pedigree of the family is shown in Figure 1.-please edit “male” to XY individual and “female” to XX individual

The figure presents a pedigree with two generations. An XY individual with involuntary sneezing when exposed to bright lights and an XX individual with involuntary sneezing when exposed to bright lights have the following four children as part of the second generation: an XX individual with involuntary sneezing when exposed to bright lights, an XY individual with no effect of light on sneezing, an XX individual with no effect of light on sneezing, and an XY individual with involuntary sneezing when exposed to bright lights.

Figure 1. Pedigree showing family members with and without symptoms

For this condition, which of the following modes of inheritance is most consistent with the observations?

A. Autosomal dominant
B. Autosomal recessive
C. X-linked dominant
D. X-linked recessive

▶️Answer/Explanation

Ans: A
Based on the pedigree, the most likely explanation is autosomal dominant inheritance. Both parents are likely heterozygous for the condition, making it possible to have two children that are not affected. The unaffected children have a homozygous recessive genotype.

Question

In pea plants, purple flower color is dominant to red flower color and long pollen grains are dominant to round pollen grains. Researchers crossed two pure-breeding lines of the pea plants to investigate whether the genes controlling flower color and pollen shape segregate independently. The procedure for the genetics experiment is summarized in Figure 1.

The figure presents the summary of a genetics experiment using pea plants. There are three rows that represent the phenotypes of three generations. The first row is labeled P Generation: Purple Flower, Long Pollen plants that are crossed with Red Flower, Round Pollen plants. An arrow points to the second row, the F 1 Generation: Purple Flower, Long Pollen plants. Four arrows point from the F 1 Generation to the third row, the F 2 Generation. Four phenotypes of plants are indicated: Purple Flower, Long Pollen plants; Purple Flower, Round Pollen plants; Red Flower, Long Pollen plants; and Red Flower, Round Pollen plants.

Figure 1. Summary of a genetics experiment using pea plants

Which of the following tables best shows the expected values in the \(F_2\) generation for a chi-square goodness-of-fit test for a model of independent assortment?

A.
B.
C.
D.
▶️Answer/Explanation

Ans: B
Because the \(F_1\) offspring used to produce the \(F_2\) generation were heterozygous for both traits, the expected phenotypic ratio for a model of independent assortment is 9:3:3:1.

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