Honors Biology
Genetics Review Sheet
Name
Block
Date
Matching
1. homozygous dominant - G
A. presence of a gene on a sex chromosome
2. genotype - E
B. a cross involving one pair of contrasting
traits
3. monohybrid cross - A
C. an alternate form of a gene
4. heredity - H
D. a genotype have two different alleles for a
trait
5. allele - C
E. the genetic makeup of an individual
6. heterozygous - D
F. a contrasting form of a hereditary
characteristic
7. trait - F
G. having two of the same dominant alleles
for a trait
8. gene - J
H. the transmission of characteristics from
parents to offspring
9. blood type - I
I.
controlled by multiple alleles
10. sex linked - A
J.
a segment of DNA that controls a
particular hereditary trait
True/False
If a statement is true, write T in the blank. If a statement is false, write F in the blank, and then in the
space provided, explain why the statement is false.
11. Offspring of the P1 generation are called the F2 generation. – False – F1 generation
12. The law of segregation states that alleles separate during the formation of gametes. - True
13. The law of independent assortment states that alleles for different traits are distributed to
gametes in pairs. – False – independently of one another.
14. An organism that is homozygous for flower color could have the genotype Qq. False heterozygous
15. Codominance occurs when both alleles for a gene are expressed in a heterozygous offspring,
such as would be seen in pink flowers. False – flowers that have red and white petals.
16. A sex-linked gene is found on one sex chromosome, but not on the other. Statement is TRUE or
FALSE depending on how you interpret the statement. If a sex-linked gene is found on the X
chromosome, then it cannot be found on the Y chromosome. However, a sex-linked gene can be
found on BOTH X chromosomes.
17. Somatic (body) cell mutations occur in sex chromosomes and can be inherited. False – cannot be
inherited. Only mutations in gametes can be inherited.
18. Polygenic traits are controlled by no more than three alleles. False – many genes with only two
alleles each.
Vocabulary Review
Define the following terms, and provide one example for each.
19. Complete dominance: RR (red) X rr (white) = all red offspring
20. Incomplete dominance: RR (red) x WW (white) = all pink offspring
21. Codominance: RR (red) x WW (white) = offspring have red and white petals
Distinguish between the terms in each of the following pairs of terms.
22. F1 generation and F2 generation: F1 generation are the offspring of the cross-pollination of P
individuals, F2 generation are the offspring of the self-pollination of F1 individuals
23. dominant allele and recessive allele: dominant alleles (capital letters) mask the presence of
recessive alleles (lowercase letters)
24. gene and allele: genes determines traits and alleles are the different forms of the genes
Multiple Choice
25. Mendel obtained plants that were pure for a particular trait by
A. Growing plants from the seeds of other plants that showed that trait
B. Discarding plants that showed other traits
C. Allowing plants to self-pollinate for several generations
D. Allowing plants to cross-pollinate for one generation
26. When Mendel crossed a strain of tall pea plants with a strain of short pea plants, he observed
that all of the plants in the F1 generation were tall. This suggests that
A. The tall trait was controlled by a dominant factor
B. The short trait was controlled by a dominant factor
C. Both traits were controlled by a recessive factor
D. The strain of short plants was not capable of pollinating the strain of tall plants.
27. A cross between pure green-podded pea plants and pure yellow-podded pea plants produces
only green podded-pea plants. When the F1 generation is allowed to self-pollinate, the F2
generation consists of
A. Only green-podded plants
B. Only yellow-podded plants
C. About ¾ yellow-podded plants and ¼ green-podded plants
D. About ¾ green-podded plants and ¼ yellow-podded plants
28. When alleles for different traits are on separate chromosomes, they are distributed to gametes
independently. This observation is summarized by the law of
A. Cross-pollination
B. Independent assortment
C. Segregation
D. Molecular genetics
29. The appearance of an organism is its
A. Genotype
B. Phenotype
C. Genotypic ratio
D. Phenotypic ratio
30. A genetic cross performed many times produces 798 long-stemmed plants and 266 shortstemmed plants. The probability of obtaining a short-stemmed plant in a similar cross is
A. 266/1064
B. 266/798
C. 798/266
D. 798/1064
31. A monohybrid cross of two individuals that are heterozygous for a trait exhibiting complete
dominance would probably result in a phenotypic ratio of
A. 4 dominant: 0 recessive
B. 1 dominant: 3 recessive
C. 3 dominant: 1 recessive
D. 1 dominant: 1 recessive
32. To determine the genotype of an individual that shows the dominant phenotype, you would
cross that individual with one that is
A. Heterozygous dominant
B. Heterozygous recessive
C. Homozygous dominant
D. Homozygous recessive
33. In a dihybrid cross between an individual with the genotype RRYY and an individual with the
genotype rryy, all of the offspring will have the genotype
A. RRYY
B. RrYY
C. RrYy
D. rryy
34. A heterozygous individual would have the genotype
A. pp
B. YY
C. Zz
D. None of these
35. In a monohybrid cross between a homozygous dominant parent and a homozygous recessive
parent, one would predict the offspring to be
A. 3/4 homozygous dominant
B. 2/4 heterozygous
C. 1/4 homozygous recessive
D. All heterozygous
36. In a monohybrid cross between two heterozygous parents, one would expect the offspring to be
A. 1 pp : 3 PP
B. 3 Pp : 1 pp
C. 1 PP : 2 Pp : 1 pp
D. All Pp
37. In guinea pigs, black fur is dominant. A black guinea pig is crossed with a white guinea pig. If the
litter contains a white offspring, the genotype of the black-haired parent is probably
A. Homozygous dominant
B. Heterozygous
C. Homozygous recessive
D. None of these
38. Segregation of alleles occurs during
A. Mitosis
B. Meiosis
C. Fertilization
D. Pollination
39. If two parents with dominant phenotypes produce an offspring with a recessive phenotype,
then probably
A. Both parents are heterozygous
B. One parent is heterozygous
C. Both parents are homozygous
D. One parent is homozygous
40. A trait occurring in 400 offspring out of a total of 1600 offspring has a probability of
A. .04
B. .25
C. .50
D. .75
41. Suppose you have found a new species of plant. Some of the plants have yellow flowers, and
some have red flowers. You cross a red-flowering plant with a yellow-flowering plant. All of the
offspring have orange flowers. Suggest a possible genotype for the offspring.
A. RR
B. Rr
C. R’R’
D. rr
42. If two genes are closely arranged on the same chromosome, they probably will
A. Cross over
B. Segregate separately
C. Control the same trait
D. Be inherited together
43. Since the ABO blood group alleles are codominant, an individual with the genotype IA IB will have
the blood type
A. Type A
B. Type B
C. Type AB
D. Type O
44. Which of the following human traits is not a polygenic trait?
A. Skin color
B. Eye color
C. Height
D. Blood type
45. If the parents of a child have the ABO blood group genotypes IA IB and ii, what the possible blood
types of the child?
A. A or B
B. A only
C. O
D. AB
46. Which of the following genotypes is possible for a person whose ABO blood type is B?
A. IB IB
B. ii
C. Both A and B
D. None of the above
Short Answer – You must write your responses on lined paper.
47. List the steps in Mendel’s experiments with pea plants. Include the P generation, F1 generation,
and F2 generation. 1) Allowed pea plants to self pollinate for many generations to produce
“true-breeding” parental plants (P generation) 2) Cross pollinated two P generation plants to
produce an F1 generation 3) Allowed the F1 generation individuals to self pollinate to produce
an F2 generation.
48. Explain how the phases of meiosis account for the law of segregation and the law of
independent assortment. Include the name of the phase and a description. The Law of
Segregation in which a pair of alleles separate during the formation of gametes occurs during
Anaphase I of meiosis. The Law of Independent Assortment in which a alleles for different genes
assort into the gametes independently of one another occurs during the random alignment of
chromosomes during Metaphase I of meiosis and the separation of homologous chromosomes
during Anaphase I of meiosis.
49. If orange flower in a plant is controlled by an allele F and red flower is controlled by an allele f,
which flower color is dominant? Explain how you know. Orange is dominant because the allele is
represented by a capital letter, F.
50. If pure orange-flowered plants are crossed with pure red-flowered plants, what will be the
flower color(s) of the F1 generation? All orange (Ff).
51. How would Mendel’s observations and conclusions have been different if many of the
characteristics he studied, such as seed color and seed texture, had been controlled by genes
located close together on the same chromosome? The genes would be inherited together,
resulting in two possible phenotypes, instead of ratios that showed four different possible
phenotypes.
52. What is the difference between homozygous and heterozygous? Homozygous genotypes have
two of the same alleles whereas heterozygous genotypes have two different alleles.
53. If the probability for a specific trait will appear in the F2 generation is 0.25, how many individuals
would be expected to show that trait in an F2 generation consisting of 80 individuals? 20
individuals.
54. A homozygous dominant individual (AA) is crossed with an individual that is heterozygous (Aa)
for the same trait. What are the possible genotypes of the offspring, and what percentage of
the offspring is likely to show the dominant phenotype? Possible genotypes of the offspring are
AA and Aa. 100% of the offspring will show the dominant phenotype.
55. Some animals, such as cows, normally produce only one offspring from each mating. If a cow
showed a dominant phenotype, why would a typical test cross be a difficult way to determine
the genotype of that animal? One offspring does not provide enough conclusive evidence to
indicate with the cow with the dominant phenotype is BB or Bb.
56. Purple flowers are completely dominant in pea plants. How can you determine the genotype of
a purple-flowering plant? Draw a Punnett square for each of the possible genotypes. Cross the
purple flower pea plant with another pea plant of the recessive phenotype, for example pp. This
is called a “test cross”. Show two Punnett squares, one for PP x pp and another for Pp x pp.
57. In tomatoes, red fruit color is dominant to yellow fruit color. Predict the genotypic ratio of
offspring produced by crossing a homozygous dominant parent with a homozygous recessive
parent. Draw a Punnett square to illustrate your prediction. RR x rr, all offspring will be red and
the genotype of the offspring is Rr. Ratio is 4:0.
58. In pea plants, yellow seeds are dominant to green seeds. Predict the genotypic ratio of offspring
produced by crossing two parents heterozygous for this trait. Draw a Punnett square to
illustrate your prediction. Ratio of YY : Yy : yy is 1 : 2 : 1
59. Describe how linked genes are an exception to Mendel’s law of independent assortment. Linked
genes are inherited together because the genes are located on the same chromosomes.
Mendel’s law of independent assortment only applies to genes that are located on different
chromosomes.
60. Distinguish between multiple-allele traits and polygenic traits. Multiple allele traits are
controlled by a single gene with more than two alleles where as polygenic traits are controlled
by many genes, each with only two alleles
Sickle cell anemia is an autosomal recessive genetic disorder that affects thousands of people in the
United States and millions worldwide. Sickle cell anemia commonly occurs in groups whose ancestors
came from Africa, as well as South America, Cuba, Central America, Saudi Arabia, India, and the
Mediterranean. Sickle cell anemia is caused by a change in the hemoglobin protein in red blood cells.
Sickle cell anemia results in paleness, fatigue, shortness of breath, and increased heart rate due to a
deficiency in the oxygen-carrying component of the blood. When oxygen levels are low in an affected
individual, the red blood cells become deformed into a curved, sickle shape.
People with sickle cell anemia can experience swelling, pain, infection, and organ damage. All
individuals have two alleles for the gene that codes for the hemoglobin protein (Hb). Individuals with
two Hb A alleles have normal, round red blood cells. Heterozygous individuals, with one Hb A allele and
one Hb S allele, do not experience symptoms of the disease, but they may produce some sickle-shaped
red blood cells. Individuals with two Hb S alleles have sickle cell anemia.
The diagrams below represent some of the steps in the formation of hemoglobin in two individuals, Y
and Z. In these diagrams, only a small part of the hemoglobin gene sequence is represented. Individual
Y has two Hb A alleles and therefore produces normal red blood cells. Individual Z has
two Hb S alleles and therefore produces sickle-shaped red blood cells.
61. In a bone marrow transplant, bone marrow from a healthy individual is transplanted into an
individual with a blood disorder.
A. Explain why a successful bone marrow transplant could treat sickle cell anemia in an
individual. Bone marrow transplants replace the diseased marrow that produces sickle-cell
blood cells with healthy marrow that will produce normal red blood cells.
B. Suppose individual Z were treated for sickle cell anemia by receiving a bone marrow
transplant. Could any children that individual Z has after the transplant inherit the gene for
the sickle cell trait? Explain your answer. Yes. A bone marrow transplant only alters the
individual’s phenotype, not the individuals genotype. The mutated allele(s) for sickle cell
anemia still exists in the individual’s gametes and therefore can be passed on to the
offspring.
Drawing Conclusions
The Punnett square below illustrates a prediction of color and texture in garden peas. Refer to the
Punnett square as you answer the following questions.
62. Does the Punnett square represent a monohybrid cross or a dihybrid cross? Explain how you
know. Dihybrid cross because it shows the inheritance of two genes, not one.
63. List the genotypes of the parents. QqTt and QqTt
64. Complete the Punnett square. Then list the genotypes predicted by the Punnett square. QQTT,
QQTt, QQtt, QqTT, QqTt, Qqtt, qqTT, qqTt, qqtt
65. Give the genotypic ratio predicted by the Punnett square for the cross. 1 : 2 : 1 : 2 : 4 : 2 : 1 : 2 : 1
66. Give the phenotypic ratio predicted by the Punnett square for the cross. 9:3:3:1
Write the possible genotypes of the offspring in the Punnett square below. Then answer the questions
in the spaces provided.
A plant with the genotype WwRr is crossed with another plant with the same genotype. Complete a
dihybrid cross and then answer the following questions.
67. What proportion of the offspring will be dominant for both traits? 9/16
68. What proportion of the offspring will have the same genotypes as their parents? 4/16 or 1/4
69. What proportion of the offspring will be homozygous dominant for both traits? 1/16
70. What proportion of the offspring will be homozygous recessive for both traits? 1/16