23.1 Review Questions
1. Which cross would best illustrate Mendel's Law of Segregation?
A. TT x tt
B. Hh x hh
C. Bb x Bb
D. rr x rr
2. In the cross Yy x Yy, what percent of offspring would have the same phenotype as the
parents?
A. 25%
B. 50%
C. 75%
D. 100%
3. In a certain plant, purple flowers are dominant to red flowers. If the cross of two purpleflowered plants produces some some purple-flowered and some red-flowered plants, what is
the genotype of the parent plants?
A. PP x Pp
B. Pp x Pp
C. pp x PP
D. pp x pp
Base questions #4-8 on the following information:
A white-flowered plant is crossed with a pink-flowered plant. All of the F1 offspring from the
cross are white.
4. Which phenotype is dominant?
5. What are the genotypes of the original parent plants?
6. What is the genotype of all the F1 offspring?
7. What would be the percentages of genotypes & phenotypes if one of the white F1 plants is
crossed with a pink-flowered plant? (You may wish to make a Punnett square to help you
answer this question.)
8. Which of Mendel's Laws is/are illustrated in this question?
9. Crossing two dihybrid organisms results in which phenotypic ratio?
A. 1:2:1
B. 9:3:3:1
C. 3:1
D. 1:1
10. The outward appearance (gene expression) of a trait in an organism is referred to as:
A. genotype
B. phenotype
C. an allele
D. independent assortment
11. In the homologous chromosomes shown in the
diagram, which is a possible alleleic pair?
A. cD
B. Ee
C. AB
D. ee
12. The phenotype of a pea plant can best be determined by:
A. analyzing its genes
B. looking at it
C. crossing it with a recessive plant
D. eating it
13. Mendel formulated his Law of Segregation after he had:
A. studied F1 offspring
B. studied F2 offspring
C. produced mutations
D. produced hybrids
14. Which cross would produce phenotypic ratios that would illustrate the Law of Dominance?
A. TT x tt
B. TT x Tt
C. Tt x Tt
D. tt x tt
15. The mating of two curly-haired brown guinea pigs results in some offspring with brown
curly hair, some with brown straight hair, some with white curly hair, and even some with white
straight hair. This mating illustrates which of Mendel's Laws?
A. Dominance
B. Segregation
C. Independent Assortment
D. Sex-Linkage
23.1 Review Questions - ANSWERED & EXPLAINED
(Red answers can be elimated due to reasons given. Blue answers are correct.)
1. Which cross would best illustrate Mendel's Law of Segregation?
A. TT x tt – all offspring will be identical (heterozygous)
B. Hh x hh – possible answer, but not the BEST answer – for the hh parent we do not know
that segregation happened because gametes will be identical
C. Bb x Bb – Best answer: Both parent show dominant trait, but some recessive offspring will
be produced (each parent carries a "b"). This means that during gamete formation, alleles
separated (segregated) and gametes had one allele only for each trait.
D. rr x rr – all offspring would be identical (homozygous dominant)
2. In the cross Yy x Yy, what percent of offspring would have the same phenotype as the
parents?
A. 25%
B. 50%
C. 75% - in the completed p-square, 3 of 4 boxes will have at least 1 "Y", producing the
dominant phenotype (same as parents)
D. 100%
3. In a certain plant, purple flowers are dominant to red flowers. If the cross of two
purple-flowered plants produces some purple-flowered and some red-flowered plants,
what is the genotype of the parent plants?
For any offspring to be recessive, each parent MUST have at least one "p, so:
A. PP x Pp – Possible answer, BUT: All offspring will show the dominant trait of purple flowers;
50% of the offspring will be homozygous dominant and 50% will be heterzygous
B. Pp x Pp – Correct answer: 75% of the offspring will be purple and 25% will be red. The
genotype ratio will be 1:2:1
C. pp x PP - only one parent is purple, this CAN'T be an answer
D. pp x pp - neither parent is purple, this CAN'T be an answer
Base questions #4-8 on the following information:
A white-flowered plant is crossed with a pink-flowered plant. All of the F1 offspring from
the cross are white.
4.
5.
6.
7.
Which phenotype is dominant? white
What are the genotypes of the original parent plants? WW (pure white) x ww (pink)
What is the genotype of all the F1 offspring? Ww (white)
What would be the percentages of genotypes & phenotypes if one of the white F1
plants is crossed with a pink-flowered plant?
50% heterozygous white & 50% homozygous recessive pink.
Why? The cross for this question would be "Ww (white F1) x
ww (pink)". The alleles of the white parent are above the
columns & those of the pink parent are in front of the rows. 2
of 4 boxes (50%) are "Ww", which is heterozygous & would
have the dominant trait (white). The other 2 of 4 boxes (50%)
are "ww", which is homozygous recessive & would have the
recessive trait (pink).
8. Which of Mendel's Laws is/are illustrated in this question?
Dominance is illustrated by the original cross (WW x ww).
9. Crossing two dihybrid organisms results in which phenotypic ratio?
A. 1:2:1 - genotype ratio of a hybrid cross, ex: Tt x Tt
B. 9:3:3:1- dihybrid means hybrid for two different traits. An example could be GgYy x GgYy.
C. 3:1 - phenotype ratio of a hybrid cross
D. 1:1
10. The outward appearance (gene expression) of a trait in an organism is referred to as:
A. genotype
B. phenotype
C. an allele
D. independent assortment
11. In the homologous chromosomes shown in the diagram, which is a possible alleleic
pair?
A. cD
B. Ee- a possible allelic pair but NOT SHOWN IN THE
DIAGRAM, so this CAN'T be an answer
C. AB
D. ee - an "allelic pair" is always two forms of the same
letter. In this example they are two lowercase "e's".
12. The phenotype of a pea plant can best be determined by:
A. analyzing its genes
B. looking at it
C. crossing it with a recessive plant
D. eating it
13. Mendel formulated his Law of Segregation after he had:
A. studied F1 offspring B. studied F2 offspring - he crossed two hybrids (F1's) and got a second generation --- the F2.
C. produced mutations - Mendel knew NOTHING about mutations so this CAN'T be an answer
D. produced hybrids
14. Which cross would produce phenotypic ratios that would illustrate the Law of
Dominance?
A. TT x tt - one parent tall, the other short, all offspring would be tall, therefore tall must be
the dominant trait over short
B. TT x Tt - both parents and all offspring will have the same phenotype, so this cross tells us
nothing about how one trait can be dominant over another
C. Tt x Tt - illustrates Segregation best
D. tt x tt - both parents and all offspring will have the same phenotype, so this cross tells us
nothing about how one trait can be dominant over another
15. The mating of two curly-haired brown guinea pigs results in some offspring with
brown curly hair, some with brown straight hair, some with white curly hair, and even
some with white straight hair. This mating illustrates which of Mendel's Laws?
A. Dominance – though we DO see dominance, this example BEST illustrated independent
assortment because there are multiple traits being studied.
B. Segregation - though we DO see segregation, this example BEST illustrated independent
assortment because there are multiple traits being studied.
C. Independent Assortment - the question involves two different traits (hair color & hair
texture), this is the only law that deals with two different traits
D. Sex-Linkage - Mendel knew NOTHING about sex-linkage so this CAN'T be an answer
REFLECTION:
What topics do you feel confident in:
____ Law of Segregation
____ Law of Independent Assortment
____ Law of Dominance
____ genotypes (homozygous dominant or recessive, or heterozygous)
____ phenotypes
____ one-trait crosses
____ two-trait crosses
____ test-crosses
____ allelic pairs (genes that are located at the same locus on a pair of homologous
chromosomes)
Make a note to yourself about what you need to review in this section: