TEST BANK
GENETICS FROM GENES TO GENOMES
8TH EDITION
CHAPTER NO. 01: MENDEL’S PRINCIPLES OF HEREDITY
Synopsis
Chapter 1 covers the basic principles of inheritance that can be summarized as Mendel’s Laws of
Segregation (for one gene) and Independent Assortment (for more than one gene).
Key terms
genes and alleles of genes – A gene determines a trait, and different alleles or forms of a
gene exist. The color gene in peas has two alleles: yellow and green.
genotype and phenotype – Genotype is the genetic makeup of an organism (written as
alleles of specific genes), while phenotype is how the organism looks.
homozygous and heterozygous – When both alleles of a gene are the same, the
individual is homozygous for that gene (or pure breeding). If the two alleles are
different, the organism is heterozygous (also called a hybrid).
dominant and recessive – The dominant allele is the one that controls phenotype in the
heterozygous genotype; the recessive allele controls phenotype only in a homozygote.
monohybrid or dihybrid cross – a cross between individuals who are both heterozygotes
for one gene (monohybrid) or for two genes (dihybrid).
testcross – performed to determine if an individual with the dominant characteristic is
homozygous or heterozygous: An individual with the dominant phenotype but
unknown genotype is crossed with an individual with the recessive phenotype.
Key ratios
3:1 – Ratio of progeny phenotypes in a cross between monohybrids
[Aa × Aa → 3 A – (dominant phenotype) : 1 aa (recessive phenotype)]
1:2:1 – Ratio of progeny genotypes in a cross between monohybrids
(Aa × Aa → 1 AA : 2 Aa : 1aa )
1:1 – Ratio of progeny genotypes in a cross between a heterozygote and a recessive homozygote
(Aa × aa → 1 Aa : 1aa )
1:0 – All progeny are the same phenotype. Can result from either of two cases:
[AA × – – → A – (all dominant phenotype)]
[aa × aa → aa (all recessive phenotype)]
9:3:3:1 – Ratio of progeny phenotypes in a dihybrid cross
(Aa Bb × Aa Bb → 9 A – B – : 3 A – bb : 3 aa B – : 1 aa bb )
,Problem Solving
The essential component of solving most genetics problems is to DIAGRAM THE CROSS in a
consistent manner. Usually, you will be given information about phenotypes, so the diagram
would be:
Phenotype of one parent × phenotype of the other parent → phenotype(s) of progeny
The goal is to assign genotypes to the parents and then use these predicted genotypes to generate
the genotypes, phenotypes, and ratios of progeny. If the predicted progeny match the observed
data you were provided, then your genetic explanation is plausible.
The points listed below will be particularly helpful in guiding your problem solving:
• Remember that two alleles of each gene exist when describing the genotypes of
individuals. But if you are describing gametes, remember that only one allele of each
gene is in a gamete.
• You will need to determine whether a character is dominant or recessive. Two main
clues will help you answer this question.
o First, if the parents of a cross are true breeding for the alternative characters of the
trait, look at the phenotype of the F1 progeny. Their genotype must be
heterozygous, and their phenotype is thus determined by the dominant allele of
the gene.
o Second, look at the F2 progeny (that is, the progeny of the F1 hybrids). The 3/4
portion of the 3:1 phenotypic ratio indicates the dominant character.
• You should recognize the need to set up a testcross (to establish the genotype of an
individual showing the dominant character by crossing this individual to a homozygote
for the recessive allele).
• You must keep in mind the basic rules of probability:
o Product rule: If two outcomes must occur together as the result of independent
events, the probability of one outcome AND the other outcome is the product of
the two individual probabilities.
o Sum rule: If there is more than one way in which an outcome can be produced,
the probability of one OR the other occurring is the sum of the two mutually
exclusive individual probabilities.
• Be aware that sometimes you need to use conditional probability, meaning that an
event’s probability is influenced by its relationship to another event that has already
occurred. You were introduced to conditional probability in Solved Problem III in this
chapter, and several of the problems in Section 1.3 require this kind of thinking. For
example, suppose you are given a pedigree diagram for a disease caused by a recessive
allele. You are asked to determine the chance that an unaffected individual is a carrier
(Dd ) when both parents are carriers. As the cross that produced the unaffected individual
is Dd × Dd, you would expect the chance of a Dd child to be 1/2. This is true, but it was
not the question you were asked! You know something about the individual in question—
which is that they are unaffected—they cannot be dd. This means that in this case, the
1 DD : 2 Dd : 1 dd ratio changes to 1 DD : 2 Dd, and the chance is 2/3 that the unaffected
, individual is a carrier. When solving probability problems in pedigrees, always think
carefully about what you know (and what you don’t know) about each individual.
• A few of the problems in this chapter will require you to use the binomial theorem, an
equation that determines how many different orders exist for two different items. For
example, suppose you want to know how many different 5-child families exist that are
composed of 2 girls and 3 boys. This is the same question as: How many ways can you
order 2 of thing a (girls) and 3 of thing b (boys)? The binomial theorem looks like this:
number of orders = T! / a! × b! where T = a + b, which is the total number of things.
Therefore, the number of ways to order 2 girls and 3 boys is:
(5 × 4 × 3 × 2 × 1) / (2 × 1)( 3 × 2 × 1) = (5 × 4)/2 = 10.
• Remember that Punnett squares are not the only means of analyzing a cross; branched-
line diagrams and calculations of probabilities using the product and sum rules can
be more efficient ways of looking at complicated crosses involving more than one or
two genes.
• Be able to draw and interpret pedigrees. When the trait is rare, look for vertical patterns
of inheritance characteristic of dominant traits, and horizontal patterns that typify
recessive traits. Check your work by assigning genotypes to all individuals in the pedigree
and verifying that these make sense.
• The vocabulary problem (the first problem in the set) is a useful gauge of how well you
know the terms most crucial for your understanding of the chapter.
Vocabulary
1.
a. phenotype 4. observable characteristic
b. alleles 3. alternate forms of a gene
c. independent 6. alleles of one gene separate into gametes randomly
assortment with respect to alleles of other genes
d. gametes 7. reproductive cells containing only one copy of each
gene
e. gene 11. the heritable entity that determines a characteristic
f. segregation 13. the separation of the two alleles of a gene into
different gametes
g. heterozygote 10. an individual with two different alleles of a gene
h. dominant 2. the allele expressed in the phenotype of the
heterozygote
i. F1 14. offspring of the P generation
j. testcross 9. the cross of an individual of ambiguous genotype
with a homozygous recessive individual
k. genotype 12. the alleles an individual has
1-3
, l. recessive 8. the allele that does not contribute to the phenotype
of the heterozygote
m. dihybrid cross 5. a cross between individuals both heterozygous for
two genes
n. homozygote 1. having two identical alleles of a given gene
Section 1.1
2. Prior to Mendel, people held two basic misconceptions about inheritance. First was the
common idea of blended inheritance: that the parental characteristics become mixed in
the offspring and forever changed. Second, many people thought that one parent
contributes the most to an offspring’s inherited features. (For example, some people
thought they saw a fully formed child in a human sperm.)
In addition, people who studied inheritance did not approach the problem in an
organized way. They did not always control their crosses. They did not look at traits with
clear-cut alternative characteristics. They did not start with pure-breeding lines. They did
not count the progeny types in their crosses. For these reasons, they could not develop
the same insights as did Mendel.
3. Several advantages exist for using peas for the study of inheritance:
• Peas have a fairly rapid generation time (at least two generations per year if
grown in the field, three or four generations per year if grown in greenhouses).
• Peas can either self-fertilize or be crossed artificially by an experimenter.
• Peas produce large numbers of offspring (hundreds per parent).
• Peas can be maintained as pure-breeding, self-fertilized lines, simplifying the
ability to perform subsequent crosses.
• Because peas have been maintained as inbred stocks, two easily distinguished
and discrete forms of many traits are known.
• Peas are easy and inexpensive to grow.
In contrast, studying genetics in humans has several disadvantages:
• The generation time of humans is very long (roughly 20 years).
• No self-fertilization occurs in humans, and it is not ethical to manipulate
crosses.
• Humans produce only a small number of offspring per mating (usually only
one) or per parent (almost always fewer than 20).
• Although people who are homozygous for a trait do exist (analogous to pure-
breeding stocks), homozygosity cannot be maintained because mating with
another individual is needed to produce the next generation.
• Because human populations are not inbred, most human traits show a
continuum of phenotypes; only a few traits have two distinct forms.
• People require a lot of expensive care to “grow”.
One major advantage exists nonetheless for the study of genetics in humans:
Because many inherited traits result in disease syndromes, and because the world’s
population is now nearly 8 billion people, a very large number of people with diverse variant
phenotypes can be recognized. These variations are the raw material of genetic analysis.
GENETICS FROM GENES TO GENOMES
8TH EDITION
CHAPTER NO. 01: MENDEL’S PRINCIPLES OF HEREDITY
Synopsis
Chapter 1 covers the basic principles of inheritance that can be summarized as Mendel’s Laws of
Segregation (for one gene) and Independent Assortment (for more than one gene).
Key terms
genes and alleles of genes – A gene determines a trait, and different alleles or forms of a
gene exist. The color gene in peas has two alleles: yellow and green.
genotype and phenotype – Genotype is the genetic makeup of an organism (written as
alleles of specific genes), while phenotype is how the organism looks.
homozygous and heterozygous – When both alleles of a gene are the same, the
individual is homozygous for that gene (or pure breeding). If the two alleles are
different, the organism is heterozygous (also called a hybrid).
dominant and recessive – The dominant allele is the one that controls phenotype in the
heterozygous genotype; the recessive allele controls phenotype only in a homozygote.
monohybrid or dihybrid cross – a cross between individuals who are both heterozygotes
for one gene (monohybrid) or for two genes (dihybrid).
testcross – performed to determine if an individual with the dominant characteristic is
homozygous or heterozygous: An individual with the dominant phenotype but
unknown genotype is crossed with an individual with the recessive phenotype.
Key ratios
3:1 – Ratio of progeny phenotypes in a cross between monohybrids
[Aa × Aa → 3 A – (dominant phenotype) : 1 aa (recessive phenotype)]
1:2:1 – Ratio of progeny genotypes in a cross between monohybrids
(Aa × Aa → 1 AA : 2 Aa : 1aa )
1:1 – Ratio of progeny genotypes in a cross between a heterozygote and a recessive homozygote
(Aa × aa → 1 Aa : 1aa )
1:0 – All progeny are the same phenotype. Can result from either of two cases:
[AA × – – → A – (all dominant phenotype)]
[aa × aa → aa (all recessive phenotype)]
9:3:3:1 – Ratio of progeny phenotypes in a dihybrid cross
(Aa Bb × Aa Bb → 9 A – B – : 3 A – bb : 3 aa B – : 1 aa bb )
,Problem Solving
The essential component of solving most genetics problems is to DIAGRAM THE CROSS in a
consistent manner. Usually, you will be given information about phenotypes, so the diagram
would be:
Phenotype of one parent × phenotype of the other parent → phenotype(s) of progeny
The goal is to assign genotypes to the parents and then use these predicted genotypes to generate
the genotypes, phenotypes, and ratios of progeny. If the predicted progeny match the observed
data you were provided, then your genetic explanation is plausible.
The points listed below will be particularly helpful in guiding your problem solving:
• Remember that two alleles of each gene exist when describing the genotypes of
individuals. But if you are describing gametes, remember that only one allele of each
gene is in a gamete.
• You will need to determine whether a character is dominant or recessive. Two main
clues will help you answer this question.
o First, if the parents of a cross are true breeding for the alternative characters of the
trait, look at the phenotype of the F1 progeny. Their genotype must be
heterozygous, and their phenotype is thus determined by the dominant allele of
the gene.
o Second, look at the F2 progeny (that is, the progeny of the F1 hybrids). The 3/4
portion of the 3:1 phenotypic ratio indicates the dominant character.
• You should recognize the need to set up a testcross (to establish the genotype of an
individual showing the dominant character by crossing this individual to a homozygote
for the recessive allele).
• You must keep in mind the basic rules of probability:
o Product rule: If two outcomes must occur together as the result of independent
events, the probability of one outcome AND the other outcome is the product of
the two individual probabilities.
o Sum rule: If there is more than one way in which an outcome can be produced,
the probability of one OR the other occurring is the sum of the two mutually
exclusive individual probabilities.
• Be aware that sometimes you need to use conditional probability, meaning that an
event’s probability is influenced by its relationship to another event that has already
occurred. You were introduced to conditional probability in Solved Problem III in this
chapter, and several of the problems in Section 1.3 require this kind of thinking. For
example, suppose you are given a pedigree diagram for a disease caused by a recessive
allele. You are asked to determine the chance that an unaffected individual is a carrier
(Dd ) when both parents are carriers. As the cross that produced the unaffected individual
is Dd × Dd, you would expect the chance of a Dd child to be 1/2. This is true, but it was
not the question you were asked! You know something about the individual in question—
which is that they are unaffected—they cannot be dd. This means that in this case, the
1 DD : 2 Dd : 1 dd ratio changes to 1 DD : 2 Dd, and the chance is 2/3 that the unaffected
, individual is a carrier. When solving probability problems in pedigrees, always think
carefully about what you know (and what you don’t know) about each individual.
• A few of the problems in this chapter will require you to use the binomial theorem, an
equation that determines how many different orders exist for two different items. For
example, suppose you want to know how many different 5-child families exist that are
composed of 2 girls and 3 boys. This is the same question as: How many ways can you
order 2 of thing a (girls) and 3 of thing b (boys)? The binomial theorem looks like this:
number of orders = T! / a! × b! where T = a + b, which is the total number of things.
Therefore, the number of ways to order 2 girls and 3 boys is:
(5 × 4 × 3 × 2 × 1) / (2 × 1)( 3 × 2 × 1) = (5 × 4)/2 = 10.
• Remember that Punnett squares are not the only means of analyzing a cross; branched-
line diagrams and calculations of probabilities using the product and sum rules can
be more efficient ways of looking at complicated crosses involving more than one or
two genes.
• Be able to draw and interpret pedigrees. When the trait is rare, look for vertical patterns
of inheritance characteristic of dominant traits, and horizontal patterns that typify
recessive traits. Check your work by assigning genotypes to all individuals in the pedigree
and verifying that these make sense.
• The vocabulary problem (the first problem in the set) is a useful gauge of how well you
know the terms most crucial for your understanding of the chapter.
Vocabulary
1.
a. phenotype 4. observable characteristic
b. alleles 3. alternate forms of a gene
c. independent 6. alleles of one gene separate into gametes randomly
assortment with respect to alleles of other genes
d. gametes 7. reproductive cells containing only one copy of each
gene
e. gene 11. the heritable entity that determines a characteristic
f. segregation 13. the separation of the two alleles of a gene into
different gametes
g. heterozygote 10. an individual with two different alleles of a gene
h. dominant 2. the allele expressed in the phenotype of the
heterozygote
i. F1 14. offspring of the P generation
j. testcross 9. the cross of an individual of ambiguous genotype
with a homozygous recessive individual
k. genotype 12. the alleles an individual has
1-3
, l. recessive 8. the allele that does not contribute to the phenotype
of the heterozygote
m. dihybrid cross 5. a cross between individuals both heterozygous for
two genes
n. homozygote 1. having two identical alleles of a given gene
Section 1.1
2. Prior to Mendel, people held two basic misconceptions about inheritance. First was the
common idea of blended inheritance: that the parental characteristics become mixed in
the offspring and forever changed. Second, many people thought that one parent
contributes the most to an offspring’s inherited features. (For example, some people
thought they saw a fully formed child in a human sperm.)
In addition, people who studied inheritance did not approach the problem in an
organized way. They did not always control their crosses. They did not look at traits with
clear-cut alternative characteristics. They did not start with pure-breeding lines. They did
not count the progeny types in their crosses. For these reasons, they could not develop
the same insights as did Mendel.
3. Several advantages exist for using peas for the study of inheritance:
• Peas have a fairly rapid generation time (at least two generations per year if
grown in the field, three or four generations per year if grown in greenhouses).
• Peas can either self-fertilize or be crossed artificially by an experimenter.
• Peas produce large numbers of offspring (hundreds per parent).
• Peas can be maintained as pure-breeding, self-fertilized lines, simplifying the
ability to perform subsequent crosses.
• Because peas have been maintained as inbred stocks, two easily distinguished
and discrete forms of many traits are known.
• Peas are easy and inexpensive to grow.
In contrast, studying genetics in humans has several disadvantages:
• The generation time of humans is very long (roughly 20 years).
• No self-fertilization occurs in humans, and it is not ethical to manipulate
crosses.
• Humans produce only a small number of offspring per mating (usually only
one) or per parent (almost always fewer than 20).
• Although people who are homozygous for a trait do exist (analogous to pure-
breeding stocks), homozygosity cannot be maintained because mating with
another individual is needed to produce the next generation.
• Because human populations are not inbred, most human traits show a
continuum of phenotypes; only a few traits have two distinct forms.
• People require a lot of expensive care to “grow”.
One major advantage exists nonetheless for the study of genetics in humans:
Because many inherited traits result in disease syndromes, and because the world’s
population is now nearly 8 billion people, a very large number of people with diverse variant
phenotypes can be recognized. These variations are the raw material of genetic analysis.
