1. health and fitness
2. disease

Biology
Concepts and Applications | 9e
Starr | Evers | Starr
Chapter 13
Observing Patterns in
Inherited Traits
© Cengage Learning 2015
© Cengage Learning 2015
13.1 How Do Alleles Contribute to Traits?
• Blending inheritance
– 19th century idea
– Failed to explain how traits disappear over
several generations and then reappear
unaltered generations later
– Charles Darwin did not accept this idea
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Mendel’s Experiments
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Mendel’s Experiments
• Gregor Mendel
– Started breeding thousands of pea plants
– Kept detailed record of how traits passed from
one generation to the next
– Began to formulate how inheritance works
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Mendel’s Experiments
• Garden pea plant is self-fertilizing
– The flowers produce male and female
gametes
• The experiments
– Controlled the pairings between individuals
with specific traits and observed traits of their
offspring
– Cross fertilized plants and collected seeds
– Recorded traits of new pea plants
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Mendel’s Experiments
• The experiments (cont’d.)
– Started with garden pea plants that “bred true”
for a particular trait – the trait stayed the same
generation after generation
– Cross-fertilized pea plants with different traits
and offspring appeared in predictable patterns
– Concluded that hereditary information is
passed in discrete units
© Cengage Learning 2015
Inheritance in Modern Terms
• Individuals share certain traits because
their chromosomes carry the same genes
• The DNA sequence of each gene occurs
at a specific location
• The location of a gene on a particular
chromosome is called a locus
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Inheritance in Modern Terms
• An individual carrying identical alleles for a
gene are homozygous
• An individual carrying two different alleles
of a gene is heterozygous
• Hybrids are heterozygous offspring of a
cross between individuals that breed true
for different forms of a trait
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Inheritance in Modern Terms
• The particular set of alleles that an
individual carries is their genotype
• The observable traits, such as flower color,
make up an individual’s phenotype
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Inheritance in Modern Terms
• An allele is dominant when its effect
masks that of a recessive allele paired
with it
– A dominant allele is represented by italic
capital letters such as (A)
– A recessive allele is represented by italic
lowercase letters such as (a)
© Cengage Learning 2015
Inheritance in Modern Terms
© Cengage Learning 2015
13.2 How Are Alleles Distributed Into
Gametes?
• A homozygous pea plant with two alleles
(PP) has purple flowers, and one with two
alleles (pp) has white flowers
• If these homozygous plants are crossed
(PP × pp), all offspring will be
heterozygous
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How Are Alleles Distributed Into Gametes?
• The allele for purple (P) is dominant over
the allele for white (p)
• Therefore, the heterozygote (Pp) will have
purple flowers
© Cengage Learning 2015
How Are Alleles Distributed Into Gametes?
• When homozygous dominant and
homozygous recessive plants are crossed
(PP × pp), only one outcome is possible
• All first generation (F1) offspring will be
heterozygous
• Genotype = Pp
• Phenotype = purple
© Cengage Learning 2015
How Are Alleles Distributed Into Gametes?
DNA replication
meiosis I
2
1
meiosis II
3
gametes (P)
gametes (p)
zygote (Pp)
© Cengage Learning 2015
How Are Alleles Distributed Into Gametes?
• Punnett square
– A grid used to predict the genetic and
phenotypic outcome of a cross
© Cengage Learning 2015
How Are Alleles Distributed Into Gametes?
male gametes
female gametes
© Cengage Learning 2015
How Are Alleles Distributed Into Gametes?
• Testcross
– Breeding experiments used to determine
genotype
– An individual that has a dominant trait (but an
unknown genotype) is crossed with one that
is homozygous recessive
© Cengage Learning 2015
How Are Alleles Distributed Into Gametes?
• Testcross
– If all offspring have dominant trait, than the
unknown genotype is homozygous for
dominant allele
– If any offspring have recessive trait, then it is
heterozygous
© Cengage Learning 2015
Phenotype
Genotype
Recessive
pp
Dominant
P?
or
Phenotype
All dominant
Conclusion
© Cengage Learning 2015
Unknown parent
is PP
1 dominant : 1 recessive
Unknown parent
is Pp
Figure 9.UN2
Testcross
Genotypes
B_
bb
Two possible genotypes for the black dog:
BB
Gametes
B
Offspring
b Bb
All black
© Cengage Learning 2015
or
Bb
B
b
b Bb bb
1 black : 1 chocolate
Figure 9.10
How Are Alleles Distributed Into Gametes?
• Monohybrid cross
– Breeding experiment in which individuals
identically heterozygous for one gene are
crossed
– Frequency of traits among offspring offers
information about the dominance relationship
between the alleles
– First generation = F1
– Second generation = F2
© Cengage Learning 2015
How Are Alleles Distributed Into Gametes?
© Cengage Learning 2015
How Are Alleles Distributed Into Gametes?
• In a monohybrid cross between two Pp
plants (Pp × Pp), the two types of gametes
can meet in four possible ways:
– Sperm P meets egg P → zygote genotype PP
– Sperm P meets egg p → zygote genotype Pp
– Sperm p meets egg P → zygote genotype Pp
– Sperm p meets egg p → zygote genotype pp
© Cengage Learning 2015
How Are Alleles Distributed Into Gametes?
• The probability that second-generation (F2)
offspring of (Pp × Pp) will have purple
flowers
– A ration of 3 purple to 1 white, or 3:1
© Cengage Learning 2015
How Are Alleles Distributed Into Gametes?
• Law of segregation
– The 3:1 phenotype ratios in F2 offspring of
monohybrid crosses became the basis of
Mendel’s law of segregation
– Diploid cells carry pairs of genes on each pair
of homologous chromosomes.
– The two genes of each pair are separated
from each other during meiosis so that they
end up on different gametes
© Cengage Learning 2015
How Are Gene Pairs Distributed Into
Gametes?
• Dihybrid cross
– Individuals identically heterozygous for alleles
of two genes (dihybrids) are crossed, and the
traits of the offspring are observed
– Frequency of traits among the offspring offers
information about the dominance relationships
between the paired alleles
© Cengage Learning 2015
How Are Gene Pairs Distributed Into
Gametes?
• One parent plant that breeds true for
purple flowers and tall stems (PPTT) is
crossed with one that breeds true for white
flowers and short stems (pptt)
• Each plant makes only one type of gamete
(PT or pt)
• All F1 offspring will be dihybrids (PpTt) and
have purple flowers and tall stems
© Cengage Learning 2015
How Are Gene Pairs Distributed Into
Gametes?
• The result of two F1 plants crossing: a
dihybrid cross (PpTt × PpTt)
• Four types of gametes can combine in
sixteen possible ways
© Cengage Learning 2015
13.4 Are All Genes Inherited in a
Mendelian Pattern?
• Simple dominance
– A dominant allele fully masks the expression
of a recessive one
• Other patterns of inheritance are not so
simple:
– Codominance
– Incomplete dominance
– Epistasis
– Pleiotropy
© Cengage Learning 2015
Are All Genes Inherited in a Mendelian
Pattern?
• Codominance
– Two alleles that are both fully expressed in
heterozygous individuals
– Multiple allele systems – gene for which three
or more alleles persist in a population
– Example: an ABO gene for blood type
© Cengage Learning 2015
Are All Genes Inherited in a Mendelian
Pattern?
• Which two of the three alleles of the ABO
gene you have determines your blood type
– The A and the B allele are codominant when
paired
• Genotype AB = blood type AB
– The O allele is recessive when paired with
either A or B
• Genotype AA or AO = blood type A
• Genotype BB or BO= blood type B
• Genotype OO = blood type O
© Cengage Learning 2015
Are All Genes Inherited in a Mendelian
Pattern?
• Incomplete dominance
– One allele is not fully dominant over another
– The heterozygous phenotype is between the
two homozygous phenotypes
© Cengage Learning 2015
Are All Genes Inherited in a Mendelian
Pattern?
• In snapdragons, one allele (R) encodes an
enzyme that makes a red pigment, and
allele (r) makes no pigment
– RR = red; Rr = pink; rr = white
• A cross between red and white (RR × rr)
yields pink (Rr)
• A cross between two pink (Rr × Rr) yields
red, pink, and white in a 1:2:1 ratio
© Cengage Learning 2015
In certain rats, black fur is dominant over white fur. If
two rats, both heterozygous for fur color, are mated,
their offspring would be expected to have?
A) four different genotypes and two different colors
B) two different genotypes and three different colors
C) three different genotypes and two different colors
D) three different genotypes and three different colors
© Cengage Learning 2015
In certain rats, black fur is dominant over white fur. If
two rats, both heterozygous for fur color, are mated,
their offspring would be expected to have?
A) four different genotypes and two different colors
B) two different genotypes and three different colors
C) three different genotypes and two different colors
D) three different genotypes and three different colors
© Cengage Learning 2015
In screech owls, red feathers are dominant
over gray feathers. If two heterozygous redfeathered owls are mated, what percentage of
their offspring would be expected to have red
feathers?
A) 25%
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B) 50%
C) 75%
D) 100%
In screech owls, red feathers are dominant
over gray feathers. If two heterozygous redfeathered owls are mated, what percentage of
their offspring would be expected to have red
feathers?
A) 25%
© Cengage Learning 2015
B) 50%
C) 75%
D) 100%
In canaries, the gene for singing (S) is
dominant over the gene for non-singing
(s). When hybrid singing canaries are
mated with non-singing canaries, what
percentage of the offspring is likely to
possess the singing trait?
A) 0% B) 25% C) 50% D) 100%
© Cengage Learning 2015
In canaries, the gene for singing (S) is
dominant over the gene for non-singing
(s). When hybrid singing canaries are
mated with non-singing canaries, what
percentage of the offspring is likely to
possess the singing trait?
A) 0% B) 25% C) 50% D) 100%
© Cengage Learning 2015
The gene for tallness (T) is dominant over the gene
for shortness (t) in pea plants. A homozygous
dominant pea plant is crossed with a heterozygous
pea plant, and 200 seeds are produced.
Approximately how many of these seeds can be
expected to produce plants that are homozygous
dominant?
A) 0
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B) 50
C) 100
D) 200
The gene for tallness (T) is dominant over the gene
for shortness (t) in pea plants. A homozygous
dominant pea plant is crossed with a heterozygous
pea plant, and 200 seeds are produced.
Approximately how many of these seeds can be
expected to produce plants that are homozygous
dominant?
A) 0
© Cengage Learning 2015
B) 50
C) 100
D) 200
In summer squash, white-colored fruit is dominant over
yellow-colored fruit. If homozygous yellow-fruited plants
are crossed with heterozygous white-fruited plants,
what is the expected percentage of fruit color produced
in the offspring?
A) 100 % yellow
C) 50% yellow, 50% white
© Cengage Learning 2015
B) 100% white
D) 25% yellow, 75% white
In summer squash, white-colored fruit is dominant over
yellow-colored fruit. If homozygous yellow-fruited plants
are crossed with heterozygous white-fruited plants,
what is the expected percentage of fruit color produced
in the offspring?
A) 100 % yellow
C) 50% yellow, 50% white
© Cengage Learning 2015
B) 100% white
D) 25% yellow, 75% white
In a certain species of mouse, gray fur (G) is dominant
over cream-colored fur (g). If a homozygous gray
mouse is crossed with a cream-colored mouse, the
genotype of the F1 generation will most likely be?
A) 100% Gg
B) 50% GG and 50% gg
C) 25% GG, 50% Gg, and 25% gg
D) 75% Gg and 25% gg
© Cengage Learning 2015
In a certain species of mouse, gray fur (G) is dominant
over cream-colored fur (g). If a homozygous gray
mouse is crossed with a cream-colored mouse, the
genotype of the F1 generation will most likely be?
A) 100% Gg
B) 50% GG and 50% gg
C) 25% GG, 50% Gg, and 25% gg
D) 75% Gg and 25% gg
© Cengage Learning 2015
In a population of dogs, curly hair is dominant
over straight hair. If two parents are
heterozygous for this trait, what is the
probability that any of their offspring will have
straight hair?
A) 0%
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B) 25%
C) 75%
D) 100%
In a population of dogs, curly hair is dominant
over straight hair. If two parents are
heterozygous for this trait, what is the
probability that any of their offspring will have
straight hair?
A) 0%
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B) 25%
C) 75%
D) 100%
A true-breeding plant that produces yellow seeds is crossed
with a true-breeding plant that produces green seeds. The F1
plants have yellow seeds. What is the expected phenotypic
ratio of seed color of the offspring of an F1 × F1 cross?
A) 1:2:1
B) 2:1
C) 3:1
D) 9:3:3:1
E) 1:1
© Cengage Learning 2015
A true-breeding plant that produces yellow seeds is crossed
with a true-breeding plant that produces green seeds. The F1
plants have yellow seeds. What is the expected phenotypic
ratio of seed color of the offspring of an F1 × F1 cross?
A) 1:2:1
B) 2:1
C) 3:1
D) 9:3:3:1
E) 1:1
© Cengage Learning 2015
Alleles are described as ______.
A) homologous chromosomes
B) environmental factors that affect gene expression
C) alternate versions of a gene
D) Punnett squares
E) alternate phenotypes
© Cengage Learning 2015
Alleles are described as ______.
A) homologous chromosomes
B) environmental factors that affect gene expression
C) alternate versions of a gene
D) Punnett squares
E) alternate phenotypes
© Cengage Learning 2015
A true-breeding plant that produces yellow seeds is
crossed with a true-breeding plant that produces green
seeds. The seeds of all of the offspring are yellow.
Why?
A) The yellow allele is recessive to the green allele.
B) All of the offspring are homozygous yellow.
C) The yellow allele is dominant to the green allele.
D) The alleles are codominant.
E) Yellow is an easier color to produce.
© Cengage Learning 2015
A true-breeding plant that produces yellow seeds is
crossed with a true-breeding plant that produces green
seeds. The seeds of all of the offspring are yellow.
Why?
A) The yellow allele is recessive to the green allele.
B) All of the offspring are homozygous yellow.
C) The yellow allele is dominant to the green allele.
D) The alleles are codominant.
E) Yellow is an easier color to produce.
© Cengage Learning 2015
In humans, the presence or absence of dimples is a
trait controlled by a single gene. What is the genotype
of an individual who is heterozygous for dimples?
A) dimples
B) DD
C) Dd
D) dd
E) DI
© Cengage Learning 2015
In humans, the presence or absence of dimples is a
trait controlled by a single gene. What is the genotype
of an individual who is heterozygous for dimples?
A) dimples
B) DD
C) Dd
D) dd
E) DI
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Which of these crosses will only produce
heterozygous offspring?
A) AA × aa
B) AA × Aa
C) Aa × Aa
D) aa × aa
E) Aa × aa
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Which of these crosses will only produce
heterozygous offspring?
A) AA × aa
B) AA × Aa
C) Aa × Aa
D) aa × aa
E) Aa × aa
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To determine the phenotype of an individual who
expresses a dominant trait, you would cross that
individual with an individual who ______.
A) expresses the dominant trait
B) is homozygous recessive for that trait
C) has the genotype Aa
D) is homozygous dominant for that trait
E) is heterozygous for that trait
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To determine the phenotype of an individual who
expresses a dominant trait, you would cross that
individual with an individual who ______.
A) expresses the dominant trait
B) is homozygous recessive for that trait
C) has the genotype Aa
D) is homozygous dominant for that trait
E) is heterozygous for that trait
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A couple has two female children. What is the
probability that their next child will be male?
A) 25%
B) 50%
C) 75%
D) 33%
E) 67%
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A couple has two female children. What is the
probability that their next child will be male?
A) 25%
B) 50%
C) 75%
D) 33%
E) 67%
© Cengage Learning 2015
An individual with (naturally) curly hair and an
individual with (naturally) straight hair mate; all of
their offspring have (naturally) wavy hair. What is the
relationship between the alleles for hair texture?
A) pleiotropy
B) incomplete dominance
C) straight hair and curly hair are sex-linked, but wavy
hair is not
D) wavy hair is dominant to both straight and curly
hair
E) codominance
© Cengage Learning 2015
An individual with (naturally) curly hair and an
individual with (naturally) straight hair mate; all of
their offspring have (naturally) wavy hair. What is the
relationship between the alleles for hair texture?
A) pleiotropy
B) incomplete dominance
C) straight hair and curly hair are sex-linked, but wavy
hair is not
D) wavy hair is dominant to both straight and curly
hair
E) codominance
© Cengage Learning 2015
An individual with (naturally) curly hair and an
individual with (naturally) straight hair mate; all of
their offspring have (naturally) wavy hair. If an
individual with wavy hair mates with an individual
with straight hair, what is the probability that their
child will have curly hair?
A) 0%
B) 25%
C) 50%
D) 75%
E) 100%
© Cengage Learning 2015
An individual with (naturally) curly hair and an
individual with (naturally) straight hair mate; all of
their offspring have (naturally) wavy hair. If an
individual with wavy hair mates with an individual
with straight hair, what is the probability that their
child will have curly hair?
A) 0%
B) 25%
C) 50%
D) 75%
E) 100%
© Cengage Learning 2015
Chromosomes that are not sex chromosomes are called
______.
A) centrosomes
B) allosomes
C) nonsexosomes
D) autosomes
E) dominant
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Chromosomes that are not sex chromosomes are called
______.
A) centrosomes
B) allosomes
C) nonsexosomes
D) autosomes
E) dominant
© Cengage Learning 2015
The parents of a child with unusual disease symptoms take the child to a
doctor for help. The doctor suspects that the condition might have a
genetic basis. She recommends that the child be taken to a specialty
clinic where physicians and staff members are trained to diagnose
genetic diseases and counsel parents. Ultimately, the child is diagnosed
with a rare recessively inherited disease. The parents are tested for the
gene, and both are found to be heterozygous. The parents want to have
another child but are afraid this child will also be affected.
What would genetic counselors say is the probability that the second
child will have the disease?
A) 1/2
B) 1/4
C) 1/8
D) 1/16
E) 1/32
© Cengage Learning 2015
The parents of a child with unusual disease symptoms take the child to a
doctor for help. The doctor suspects that the condition might have a
genetic basis. She recommends that the child be taken to a specialty
clinic where physicians and staff members are trained to diagnose
genetic diseases and counsel parents. Ultimately, the child is diagnosed
with a rare recessively inherited disease. The parents are tested for the
gene, and both are found to be heterozygous. The parents want to have
another child but are afraid this child will also be affected.
What would genetic counselors say is the probability that the second
child will have the disease?
A) 1/2
B) 1/4
C) 1/8
D) 1/16
E) 1/32
© Cengage Learning 2015
10/8 Protein Synthesis
9
10/10
Genes
10
10/15
Mitosis
11
10/17
Meiosis
12
10/22
Genotype &
Phenotype
13
10/24
Biotechnology
14
10/29
Exam #2
10/31
Begin Evolution
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