Genetics Review
1. Why are Mendel’s discoveries important?
2. What are three reasons the garden pea is a good subject for studying heredity?
3. Identify the three main steps for producing a monohybrid cross.
Complete each statement by writing the correct term or phrase in the space provided.
4. Physical features that are inherited are called ______________________.
5. A(n) ______________________ is one of several possible variations of a character.
6. The first group of parents that are crossed in a breeding experiment is called the ______________________
generation.
7. In Mendel’s experiment, the ______________________ generation was obtained by cross-pollinating the P
generation.
8. The ______________________ generation in Mendel’s experiment showed both forms of the trait in a ratio of
3:1.
Section: Mendel’s Theory
In the space provided, write the letter of the description that best matches the term or phrase.
9. _____ alleles
a. when two different alleles are present, the allele that is completely
expressed
10. _____ dominant
b. when two alleles of a particular gene are the same
11. _____ recessive
c. when two alleles of a particular gene are different
d. an organism’s physical appearance
12. _____ homozygous
e. the set of alleles that an organism has
13. _____ heterozygous
f. different forms of a gene
g. when two different alleles are present, the allele that has no observable
14. _____ genotype
effect on the organism’s
15. _____ phenotype
Complete each statement by writing the correct term or phrase in the space provided.
16. If the allele for yellow peas is Y, the allele for the contrasting trait, green peas, is _____________________.
17. If Tt is the genotype of a plant, where T stands for tall and the recessive allele stands for short, its phenotype is
______________________.
18. If tt is the genotype of a plant, where T stands for tall and the recessive allele stands for short, its phenotype is
______________________.
Read each question, and write your answer in the space provided.
19. What is the law of segregation?
20. What is the law of independent assortment?
Section: Modeling Mendel’s Laws
Complete each statement by writing the correct term or phrase in the space provided.
21. In a testcross to determine if an individual with a dominant phenotype is heterozygous or homozygous for the
character, you always cross the individual with a homozygous ______________________ individual.
22. If the offspring of a testcross all have the dominant trait, then the genotype of the individual being tested is
______________________.
23. If some of the offspring of a testcross have the recessive trait, then the genotype of the individual being tested
is ______________________.
24. The probability that a gamete from a plant with a Tt genotype will carry a t allele is ______________________.
25. The probability of homozygous recessive offspring resulting from a cross between two homozygous dominant
individuals is ______________________.
26. The probability of heterozygous offspring resulting from a cross between two heterozygous individuals is
______________________.
Read each question, and write your answer in the space provided.
27. When studying a pedigree, how do scientists determine if a trait is sex-linked?
28. When studying a pedigree, how do scientists determine if an autosomal trait is dominant or recessive?
Section: Beyond Mendelian Heredity
In the space provided, explain how the terms in each pair differ in meaning.
29. polygenic character, multiple alleles
30. incomplete dominance, codominance
Complete each statement by writing the correct term or phrase in the space provided.
31. Sometimes several genes affect a character, resulting in a(n) ______________________ character.
32. ______________________ genes are close together on the same chromosome.
Read each question, and write your answer in the space provided.
33. How are characters affected by the environment?
34. Why would closely linked genes be an exception to the law of independent assortment during meiosis?
35. Pisum sativum, the garden pea, is a good subject to use in studying heredity for all of the following reasons
except
a. Several varieties of Pisum sativum are available that differ in easily distinguishable traits.
b. Pisum sativum is a small, easy-to-grow plant.
c. Pisum sativum matures quickly and produces a large number of offspring.
d. A Pisum sativum plant with male reproductive parts must crosspollinate with a plant having female
reproductive parts for reproduction to take place.
36. Step 1 of Mendel’s garden pea experiment, allowing each variety of garden pea to self-pollinate for several
generations, produced the
a. F1 generation.
c. P Generation.
b. F2 generation.
d. P2 generation.
37. In the F2 generation in Mendel’s experiments, the ratio of dominant to recessive phenotypes was
a. 1:3
c. 2:1
b. 1:2
d. 3:1.
38. The trait that was expressed in the F1 generation in Mendel’s experiment is considered
a. recessive.
c. second filial.
b. dominant.
d. parental.
39. Mendel’s law of segregation states that
a. pairs of alleles are dependent on one another when separation occurs during gamete formation.
b. pairs of alleles separate independently of one another after gamete formation.
c. each pair of alleles remains together when gametes are formed.
d. the two alleles for a gene separate when gametes are formed.
40. A series of genetic crosses results in 787 long-stemmed plants
and 277 short-stemmed plants. The probability that you will
obtain short-stemmed plants if you repeat this experiment is:
41. Crossing a snapdragon that has red flowers with one that has
white flowers produces a snapdragon that has pink flowers. The
trait for flower color exhibits
a. multiple alleles.
c. incomplete dominance.
b. complete dominance.
d. codominance.
42. Which of the following is not considered a simple Mendelian inheritance pattern?
a. recessive/dominant traits
c. polygenic inheritance
b. law of segregation
d. law of independent assortment
43. On which of the following chromosomes would a sex-linked gene more often be found in humans?
a. X
c. O
b. Y
d. YO
44. The human blood groups are an example of
a. homozygous alleles.
c. incomplete dominance.
b. codominance.
d. Both (a) and (c)
Refer to the figure at right, which represents a monohybrid cross between two individuals that are heterozygous for
a trait.
45. If the resulting phenotypic ratio is 3:1, the missing parental allele is
a. d.
c. Dd.
b. D.
d. DD.
46. The two unknown genotypes in the offspring are
a. DD and dd.
c. dd and DD.
b. Dd and Dd.
d. Dd and dd.
47. Which of the following summarizes one of Mendel’s major hypotheses developed from his studies of garden
peas?
a. All of an individual’s alleles make up its genotype.
b. Traits that are intermediate between two parents are caused by genes that are incompletely
dominant.
c. There are alternative versions of genes, which are now called alleles.
d. When two dominant alleles are expressed together, they are called codominant.
48. Which of the following is an example of a testcross?
a. YY x YY
c. Yy x Yy
b. YY x yy
d. All of the above
49. What is the relationship between genotype and phenotype?
a. Phenotype determines a genotype.
b. Genotype produces a phenotype.
c. Genotype and phenotype give rise to alleles.
d. None of the above
Question 16 refers to the figure below, which shows the inheritance of sickle cell
anemia in a family.
50. Which of the following is true based on the information provided in the
pedigree?
a. Both parents have sickle cell anemia.
b. Both parents carry an allele for sickle cell anemia.
c. Sickle cell anemia is caused by a dominant allele.
d. All three children are carriers of a defective gene that causes
sickle cell anemia.
Complete each statement by writing the correct term or phrase in the space
provided.
51. The investigator whose studies formed the basis of modern genetics is ______________________ .
52. The ______________________ , or detectable trait, of an individual is determined by the alleles that code for
traits. The set of alleles that an individual has is called its ______________________.
53. A cross between a pea plant that is true-breeding for green pod color and one that is true-breeding for yellow
pod color is an example of a(n) ______________________ cross.
54. Characteristics such as eye color, height, weight, and hair and skin color are examples of
___________________ _____________________ because several genes act together to influence a character.
55. Genes that are close together on the same chromosome are said to be ______________________.
Read each question, and write your answer in the space provided.
56. What approximate ratio of plants expressing contrasting traits did Mendel calculate in his F2 generation of
garden peas? What steps did he take to calculate this ratio?
57. Name Mendel’s two major laws of heredity.
58. Give an example of how the environment might influence gene expression.
59. Describe the inheritance of sex-linked genes.
Answers:
1. They are important because they serve as
the foundation for our current
understanding of genetics and heredity.
2. Has traits that come in two forms, one
dominant, the other recessive. Grows
quickly. Can cross and self-pollinate.
3. P generation (2 true-breeders of
contrasting traits)  F1 generation (all
dominant form, cross pollinated)  F2
generation (recessive trait showed up in a
1:3 ratio with the dominant form).
4. Traits or characters
5. Allele
6. Parental
7. 1st filial, F1
8. 2nd filial, F2
9. F
10. A
11. G
12. B
13. C
14. E
15. D
16. y
17. tall
18. short
19. alleles for a gene separate during the
creation of gametes
20. the assortment of alleles into gametes for
one gene does not influence the
assortment of alleles for another gene (if
they are not linked)
21. recessive
22. homozygous dominant
23. heterozygous
24. 50%
25. 0%
26. 50%
27. If it appears more often in males than
females, especially if females do not show
the trait
28. If it’s dominant then at least one parent of
the offspring showing the trait must also
show the trait. If not, then it’s recessive.
29. Polygenic = multiple gene influence the
trait, multiple alleles = one gene has more
than 2 alleles
30. Incomplete = two alleles mix their
phenotypes in an intermediate form (like
mixing paint), codominant = two alleles
share half of the phenotype at the same
time (like mixing marbles)
31. Polygenic
32. Linked
33. Can be temperature, nutrient,
conditionally, environmentally dependent.
34. Linked genes violate the law of
independent assortment.
35. D
36. C (it should be “P” generation)
37. D
38. B
39. D
40. A
41. C
42. C
43. A
44. B
45. A
46. D
47. C
48. B
49. B
50. B
51. Gregor Mendel
52. Phenotype, Genotype
53. Monohybrid
54. Polygenic character
55. Linked
56. 3 dominant:1 recessive
57. Segregation, Independent Assortment
58. Many examples; snowshoe rabbits are
white in winter, brown in summer =
temperature dependent
59. Usually associated with ‘X’ crhomosomes.
Sex-linked genes will show up more in one
sex than the other. Usually males because
they have 1 ‘X’ chromosome inherited
from mom, who is always the carrier of Xlinked traits.