Practice Exam Questions Week 1

Question 1

In a diploid individual, one chromosome carries A and B genes, and the homologous chromosome carries different forms (alleles) of these same genes, a and b. If there is a single crossover between these two genes involving non-sister chromatids during metaphase I of meiosis, the resulting four gametes are:

AB, AB, ab, ab.

AB, ab, AB, ab.

AaBb, AaBb, AaBb, AaBb.

AB, Ab, aB, ab.

Ab, Ab, aB, aB.

Answer 1

AB, Ab, aB, ab.

Question 2

Parents A & B have 4 offspring One Male Affected, One Female Unaffected, One Female Affected, and 1 Male Unaffected

Assuming that the trait represented by the filled symbols below is a rare inherited trait with complete penetrance due to a single gene with alleles A and a, what mode of inheritance does the pedigree suggest?

dominant

recessive

Answer 2

recessive

Question 3

Parents A & B have 4 offspring One Male Affected, One Female Unaffected, One Female Affected, and 1 Male Unaffected

In the pedigree above, what can you say about the likely genotypes of individuals A and B?

both are AA

one is AA and the other is Aa

both are Aa

It is not possible to determine this for certain from the information provided.

Answer 3

both are Aa

Question 4

In humans, ability to roll the tongue (R) is dominant to being unable to roll (r). Having freckles (F) is dominant to having no freckles (f). A freckled tongue-roller could have which of the following genotypes?

RRFF

RrFf

rrFF

RRFF and RrFf only

All of these choices are correct.

Answer 4

RRFF and RrFf only

Question 5

You are given two populations of true-breeding tomato plants with two simple dominant/recessive traits that sort independently. Using the multiplication rule, how many different phenotypic combinations would you expect to see in the F2 generation? In what phenotypic ratio?

two, 3:1

three, 9:6:1

four, 9:3:3:1

Answer 5

four, 9:3:3:1

Question 6

A pea plant is heterozygous (Aa) for seed color and heterozygous (Bb) for seed shape. According to Mendel’s principle of independent assortment: (Select all that apply.)

each gamete will contain either a seed-color allele or a seed-shape allele, but not both.

a gamete that contains dominant allele for seed color must also contain the dominant allele for seed shape.

a gamete that contains dominant allele for seed color must also contain the recessive allele for seed shape.

a gamete that contains the dominant allele for seed color is equally likely to contain the dominant or the recessive allele for seed shape.

possible gamete genotypes are AB or ab; each is equally likely to occur.

Answer 6

a gamete that contains the dominant allele for seed color is equally likely to contain the dominant or the recessive allele for seed shape.

possible gamete genotypes are AB or ab; each is equally likely to occur.

Question 7

In genetics, the dash symbol (–) is a “wild card” that stands for either the dominant allele or the recessive allele; for example, A– means the individual has either the genotype AA or Aa. Two genes that undergo independent assortment affect coat color in the house mouse. Each gene has two alleles, one of which is dominant for coat color. Genotypes of the form A– B– have a brownish color called agouti, those of the form A– bb are black, and those of the form aa B– and aa bb are albino (white). What ratio of agouti : black : white is expected from the cross Aa Bb × Aa Bb?

10: 3:3
9: 3:4
12: 3:1
9: 6:1

Answer 7

9:3:4

Question 8

Consider a gene with four alleles A1, A2, A3, and A4. How many distinct heterozygous genotypes are possible?

2

3

4

5

6

Answer 8

6

Question 9

Consider a gene with four alleles A1, A2, A3, and A4. If the cross A1A2 × A3A4 yields two offspring, what is the probability that both of them have the same genotype?

1/8

1/4

1/3

1/2

3/4

Answer 9

1/4

Question 10

Consider a gene with n alleles A1, A2, …, An. How many distinct genotypes are possible, taking into account both homozygous and heterozygous genotypes?

n2

n2/2

n(n –1)

n(n – 1)/2

n(n + 1)/2

Answer 10

n(n + 1)/2

Question 11

Among the progeny of a heterozygous round (Aa) × homozygous wrinkled (aa) testcross, three seeds are chosen at random. What is the probability that all three seeds are round?

(1/2)3

2(1/2)3

3(1/2)3

4(1/2)3

Answer 11

(1/2)3

Question 12

In the F2 generation of a homozygous round (AA) × homozygous wrinkled (aa) cross in peas, three seeds are chosen at random. What is the probability that two seeds are round and the other is wrinkled?

(1/4)3

3(1/4)(3/4)2

3(1/4)2(3/4)

(3/4)3

Answer 12

3(1/4)(3/4)2

Question 13

Consider a gene with four alleles A1, A2, A3, and A4. In the cross A1A2 × A3A3, how many offspring genotypes are possible?

2

3

4

5

6

Answer 13

2

Question 14

A true-breeding black rabbit is crossed with a true-breeding white rabbit to produce an F1 generation of 15 individuals. If the black color trait is dominant, which of the following represents the expected phenotype of an F1 generation cross?

15 black rabbits, 0 white rabbits, 0 grey rabbits

5 black rabbits, 5 white rabbits, 6 grey rabbits

0 black rabbits, 0 white rabbits, 15 grey rabbits

5 black rabbits, 3 white rabbits, 7 grey rabbits

0 black rabbits, 15 white rabbits, 0 grey rabbits

Answer 14

15 black rabbits, 0 white rabbits, 0 grey rabbits

Question 15

In a population of organisms with 4 alleles, how many homozygous genotypes are possible? How many heterozygous genotypes are possible?

3; 4

4; 3

4; 4

4; 6

4; 10

Answer 15

4; 6

Question 16

Flower color in snapdragons is due to a gene with incomplete dominance: CRCR plants have red flowers, CRCW have pink flowers, and CWCW plants have white flowers. Which cross is expected to yield progeny that all have pink flowers?

CRCR × CRCW

CRCR × CWCW

CRCW × CRCW

CRCW ×CWCW

CWCW × CWCW

Answer 16

CRCR × CWCW

Question 17

In genetics, the dash symbol (–) is a “wild card” that stands for either the dominant allele or the recessive allele; for example, A– means the individual has either the genotype AA or Aa. Two genes that undergo independent assortment affect flower color in sweet peas. Each gene as two alleles, one of which is dominant for flower color. Genotypes of the form A– B– have purple flowers, whereas those of the form A– bb, aa B–, and aa bb have white flowers. What ratio of purple : white is expected from the cross Aa Bb × Aa Bb?

Hint: This type of epistasis is known as “duplicate recessive epistasis.”

9: 7
10: 6
12: 4
13: 3
15: 1

Answer 17

9:7

Question 18

Imagine that a rancher has a herd of cattle with brown hides and short horns. All of his cattle are also relatively short in stature. If all of these traits were true-breeding, what could you say about the progeny of these cattle?

It is impossible to determine the traits of such progeny―they will likely demonstrate different hide colors, horn lengths, and heights.

The progeny of these cattle will have short horns, but a variety of hide colors and heights.

The progeny of these cattle will have brown, black, white, and spotted hides.

Because the cattle are true-breeding, the progeny of this herd will all be sterile.

The progeny of these cattle will be short in stature and have brown hides and short horns.

Answer 18

The progeny of these cattle will be short in stature and have brown hides and short horns.

Question 19

If you crossed two heterozygous yellow-seed pea plants (genotypes Aa), the relative frequency of:

the a allele in each parent’s gametes would be 1/2.

the A allele in each parent’s gametes would be 1/2.

green-seed plants (genotype aa) would be 1/4.

homozygous yellow-seed plants (genotype AA) would be 1/4.

All of these choices are correct.

Answer 19

All of these choices are correct.

Question 20

In genetics, the dash symbol (–) is a “wild card” that stands for either the dominant allele or the recessive allele; for example, W– means the individual has either the genotype WW or Ww. In summer squash, genotypes W– G– and W– gg are white, ww G– are yellow, and ww gg are green. W and G show independent assortment. What is the ratio of white : yellow : green among progeny of the cross Ww Gg × Ww Gg?

12: 3:1
9: 3:1
10: 3:3
9: 6:1

None of the answer options is correct.

Answer 20

12:3:1

Question 21

With independent assortment, the ratio of genotypes in the F2 generation of a cross between true-breeding strains (AA bb × aa BB) can be described as 1:2:1:2:4:2:1:2:1. To what genotype does the “4” in the ratio refer?

AA Bb

Aa BB

Aa Bb

None of the answer options is correct.

Answer 21

Aa Bb