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CHAPTER
11
MENDELIAN PATTERNS OF INHERITANCE
Chapter Outline
11.1 Gregor Mendel
1. Mendel was an __________________ monk.
2. Mendel formulated two fundamental laws of heredity in the early __________________.
3. He had previously studied science and __________________ at the University of Vienna.
4. At time of his research, he was a __________________ science teacher at a local technical high
school.
5. Prior to Mendel’s work, investigators had been trying to support a “__________________” concept of
__________________.
A. Blending Concept of Inheritance
1. This theory stated that offspring would have traits __________________ between those of the parents.
2. Red and white flowers produce __________________ flowers; any return to red or white offspring
was considered instability in the __________________ material.
3. Charles Darwin wanted to develop a theory of __________________ based on hereditary principles;
__________________ theory was of _____________ help.
a. A blending theory did not account for variation (differences) and could not explain species
diversity.
b. The particulate theory of __________________ proposed by Mendel can account for presence of
__________________ among members of a population __________________ after
__________________.
c. Mendel’s work was unrecognized until __________________; Darwin was never able to use it to
__________________ his theory of __________________.
B. Mendel’s Experimental Procedure
1. Because Mendel had a __________________ background, he used a __________________ basis for
his breeding __________________.
2. Mendel prepared his experiments __________________ and conducted preliminary studies.
a. He chose the __________________, Pisum sativum, because peas were easy to
culti__________________ vate, had a __________________ generation time, and could be
__________________ -pollinated by hand.
b. From many __________________, Mendel chose __________________ true-breeding varieties
for his __________________.
c. __________________ varieties had all offspring __________________ the parents and
__________________ each other.
d. Mendel studied __________________ traits (e.g., seed __________________ and
__________________, flower __________________, etc.).
3. Mendel traced __________________ of individual traits and kept careful records of
__________________.
4.
5.
He used his understanding of mathematical principles of __________________ to interpret results.
He arrived at a particulate theory of __________________ because it is based on the existence of
minute particles—now called __________________.
11.2 Mendel’s Laws:
Law of Segregation
1. Mendel confirmed that his __________________ plants always had __________________ offspring,
i.e., were __________________, before crossing two __________________ strains that differed in
only one trait—this is called a __________________ cross.
2. A monohybrid cross is between __________________ parent organisms true-breeding for
__________________ distinct forms of __________________ trait.
3. Mendel tracked each trait through __________________ generations.
a. __________________ is the parental generation in a breeding experiment.
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b. __________________ is the first-generation offspring in a breeding experiment.
c. __________________ is the second-generation offspring in a breeding experiment.
4. He performed reciprocal crosses, i.e. pollen of __________________ plant to stigma
of __________________ plant and vice versa.
5. His results were __________________ to those predicted by a blending theory of
__________________.
6. He found that the F1 plants resembled only __________________ of the parents.
7. Characteristics of other parent __________________ in about __________________ of F 2 plants;
__________________ of offspring resembled the F 1 plants.
8. Mendel saw that these __________________ results were possible if:
a. F1 hybrids contained __________________ factors for each trait, one being __________________
and the other __________________;
b. factors __________________ when gametes were formed; a gamete carried
__________________ copy of each factor;
c. and random __________________ of all possible gametes occurred upon __________________.
9. Results of his experiments led Mendel to develop his first law of inheritance—the
__________________:
a. Each organism contains __________________ factors for each trait.
b. Factors __________________ in the formation of gametes.
c. Each __________________ contains __________________ factor for each trait.
d. Fertilization gives each __________________ individual __________________ factors for each
trait.
A. As Viewed by Modern Genetics
1. Each trait in a pea plant is controlled by __________________ alleles, alternate forms of a gene that
occur at the __________________ gene locus on __________________ chromosomes.
2. A __________________ allele masks or __________________ expression of a __________________
allele; it is represented by an __________________ letter.
3. A __________________ allele is an allele that exerts its effect only in the __________________ state;
its expression is __________________ by a dominant allele; it is represented by a
__________________ letter.
4. The __________________ is the specific __________________ of alleles on __________________
chromosomes.
5. The process of __________________ explains Mendel’s law of __________________.
6. In Mendel’s cross, the parents were true-breeding; each parent had __________________ identical
alleles for a trait–they were __________________, indicating they possess __________________
identical alleles for a trait.
7. __________________ __________________ genotypes possess __________________ dominant
alleles for a trait.
8. __________________ __________________ genotypes possess two __________________ alleles for
a trait.
9. After cross-pollination, all individuals of the F1 generation had __________________ of each type of
__________________.
10. __________________ genotypes possess __________________ of each allele for a particular trait.
11. The allele not expressed in a __________________ is a recessive allele.
B. Genotype Versus Phenotype
1. Two organisms with different allele combinations can have the same outward appearance (e.g.,
__________________ and __________________ pea plants are both __________________; therefore,
it is necessary to distinguish between alleles present and the __________________ of the organism).
2. __________________ refers to the alleles an individual receives at fertilization (dominant, recessive).
3. __________________ refers to the physical __________________ of the individual (tall, short, etc.).
C. One-trait Genetics Problems
1. First determine which characteristic is __________________; then code the alleles involved.
2. Determine the __________________ and gametes for both parents; an individual has two alleles for
each __________________; each gamete has only one allele for each trait.
3. Each gamete is __________________; each has a 50% chance of __________________ either allele.
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D. Laws of Probability
1. __________________ is the likely outcome a given event will occur from __________________
chance.
a. For example, with every coin flip there is a __________________ chance of heads and
__________________ chance of tails.
b. Chance of inheriting one of either two alleles from a parent is also __________________
2. The multiplicative law of probability __________________ that the chance of two or more
__________________ events occurring together is the product of the probability of the events
occurring separately.
a. The chance of inheriting a specific allele from one parent and a specific allele from another is ½ x
½ or __________________
b. Possible combinations for the alleles __________________ of heterozygous parents are the
following:
EE = ½ x ½ = _____, eE = ½ x ½ = _____,Ee = ½ x ½ = ¼, ee = ½ x ½ = _____
3. The additive law of probability __________________ the probability of an event that occurs in
__________________ or more independent ways; it is the __________________ of individual
probabilities of each way an __________________ can occur; in the above example where
__________________ earlobes are __________________ (EE, Ee, and eE), the chance for unattached
earlobes is 1/4 + 1/4 + 1/4 = 3/4.
E. The Punnett Square
1. The __________________ square was introduced by R. C. Punnett (early 1900s) and provides a
simple method to __________________ the probable results of a genetic cross.
2. In a Punnett square, all possible __________________ of sperm alleles are lined up vertically and all
possible egg alleles are lined up horizontally; every possible combination is __________________ in
squares.
3. The larger the sample size __________________, the more likely the outcome will reflect
__________________ ratios; a large number of offspring must be counted to observe the
__________________ results; only in that way can all possible genetic types of sperm
__________________ all possible types of eggs.
4. Specific crosses in __________________ cannot be done in order to count many offspring; therefore
in humans, the __________________ ratio is used to estimate the probability of any child having a
__________________ characteristic.
5. Punnett square uses laws of __________________; it does not dictate what the next child will
__________________.
6. “Chance has no __________________”: if two heterozygous parents have a first child with attached
earlobes (likely in 1/4th of children), a second child born still has __________________ chance of
having attached earlobes.
F. One-Trait Testcross
1. To confirm that the F1 was __________________, Mendel crossed his F1 plants with
__________________ __________________ plants.
2. Results indicated the __________________ factor was present in the F1 plants; they were thus
__________________.
3. A monohybrid __________________ is used between an individual with dominant phenotype and an
individual with a recessive phenotype to see if the individual with dominant phenotype is
__________________ or __________________.
Mendel’s Law of Independent Assortment
1. This two-trait (__________________) cross is between two parent organisms that are true-breeding for
different forms of __________________ traits; it produces offspring heterozygous for both traits.
2. Mendel observed that the F1 individuals were __________________ in both traits.
3.. He further noted __________________ phenotypes among F2 offspring; he deduced second law of
heredity.
4. Mendel’s law of __________________ assortment states that members of __________________ pair
of factors assort __________________ of members of another pair, and that all __________________
of factors occur in gametes.
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A. Two-trait Genetics Problems
1. Laws of probability indicate a __________________ phenotypic ratio of F2 offspring resulting in the
following:
a. 9/16 of the offspring are __________________ for both traits;
b. 3/16 of the offspring are __________________ for one trait and recessive for the other trait;
c. 3/16 of the offspring are __________________ and recessive opposite of the previous
proportions; and
d. 1/16 of the offspring are __________________ for both traits.
2. The Punnett Square for two-trait crosses
a. A larger __________________ square is used to calculate probable results of this cross.
b. A phenotypic ratio of __________________ is expected when heterozygotes for two traits are
crossed and simple __________________ is present for both genes.
c. __________________ __________________ during __________________ explains these results.
B. Two-Trait Testcross
1. A two-trait __________________ tests if individuals showing two dominant characteristics are
__________________ for both or for one trait only, or heterozygous for both.
2. If an organism heterozygous for two traits is crossed with another recessive for both traits, the
expected phenotypic ratio is __________________
3. In __________________ genetics problems, the individual has four alleles, two for each
__________________.
11.3 Human Genetic Disorders
A. Patterns of Inheritance
1. Genetic disorders are medical conditions caused by __________________ inherited from parents.
2. An __________________ is any chromosome other than a sex (__________________) chromosome.
3. In a __________________ chart, males are designated by squares, __________________ by circles;
shaded circles and squares are __________________ individuals; line __________________ square
and circle represents a union; __________________ line leads to offspring.
4. A __________________ is a heterozygous individual with __________________ apparent
abnormality but able to pass on an allele for a recessively-inherited genetic disorder.
5. Autosomal dominant and autosomal recessive alleles have __________________ patterns of
inheritance.
a. Characteristics of autosomal dominant disorders
1) __________________ children usually have an affected parent.
2) __________________ are affected.: two affected parents can produce unaffected child; two
unaffected parents will not have __________________ children.
b. Characteristics of autosomal recessive disorders
1) Most affected children have __________________ parents since heterozygotes have a
__________________ phenotype.
2) Two affected parents always produce an __________________ child.
3) Close __________________ reproduce together are more likely to have
__________________ children.
B. Autosomal Recessive Disorders
1. Tay-Sachs Disease
a. Usually occurs among __________________ people in the U.S. of central and eastern
__________________ descent.
b. Symptoms are not __________________ apparent; infant’s development begins to slow between
four to eight __________________, neurological and psychomotor __________________ become
apparent, child gradually becomes __________________ and helpless, develops
__________________, eventually becomes paralyzed and __________________ by age of three
or four.
c. This results from lack of __________________ hexosaminidase A (Hex A) and the subsequent
storage of its substrate, glycosphingolipid, in __________________.
d. Primary sites of storage are cells of the __________________; accounts for progressive
__________________.
e. There is __________________ treatment or cure.
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f. Prenatal diagnosis is __________________ by amniocentesis or chorionic villi sampling.
g. The gene is located on chromosome __________________
2. Cystic Fibrosis
a. This is the most common __________________ genetic disease in Caucasians in the U.S.
b. About 1 in 20 Caucasians is a __________________, and about 1 in 3,000 newborns has this
disorder.
c. An __________________ production of a viscous form of __________________ in the
__________________ and pancreatic ducts is seen.
1) The resultant __________________
2) Digestive enzymes must be __________________ with food to supplant the pancreatic
__________________.
d. New __________________ have raised the average life expectancy to up to
__________________ years.
e. Chloride ions (Cl–) fail to pass __________________ membrane proteins.
f. Since water normally follows Cl–, lack of __________________ in the lungs causes thick
__________________.
g. The cause is a gene on chromosome __________________; __________________ to insert the
gene into nasal epithelium has had __________________ success.
h. __________________ testing for adult carriers and fetuses is possible.
3. Phenylketonuria (PKU)
a. PKU occurs once in every __________________ births; it is the most common
__________________ disease of the __________________ system.
b. It is caused by a lack of an __________________ needed to metabolize amino acid phenylalanine;
this results in __________________ of the amino acid in nerve cells of the __________________
and impairs nervous system development.
c. PKU is caused by a gene on chromosome __________________
d. __________________ are routinely tested in the hospital for high levels of phenylalanine in the
__________________.
e. If an infant has PKU, the child is placed on a diet __________________ in phenylalanine until the
brain is fully developed, near age __________________.
4. Sickle-Cell Disease
a. This __________________ is the most common inherited disorder in blacks, affecting about 1 in
500 African Americans.
b. The gene is on chromosome __________________.
c. In affected individuals, the __________________ are shaped like sickles—an abnormal
hemoglobin molecule, Hbs, causes the __________________.
1) Normal hemoglobin, HbA, differs from Hbs by __________________ amino acid in the
protein globin.
d. The disease is an example of pleiotropy, describing a gene that affects more than one
__________________ of an individual.
e. Sickling of the __________________ occurs when the oxygen content of the person’s blood is
__________________, thereby slowing down blood flow and __________________ small
vessels.
f.
Signs and symptoms include __________________, weakness, fever, pain, rheumatism,
__________________ resistance to disease, kidney and heart failure.
g. Treatment includes __________________ management, blood __________________, and bone
marrow __________________.
h. The disease can be diagnosed __________________.
i.
Individuals with the sickle cell trait (__________________), who normally do not have any
sickle-shaped cells unless they experience __________________ or mild oxygen deprivation, are
resistant to the disease __________________.
C. Autosomal Dominant Disorders
1. Neurofibromatosis
a. This is an __________________ dominant disorder that affects one in 3,500 newborns and is
distributed __________________ around the world.
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b.
Affected individuals have __________________ skin spots at birth, which develop into
__________________ tumors.
c. Neurofibromas are __________________ under the skin comprised of fibrous coverings of
nerves.
d. In most cases, symptoms are mild and patients live a __________________ life; sometimes
symptoms are __________________:
1) __________________ deformities, including a large head;
2) eye and ear __________________ that can lead to blindness and hearing loss; and
3) learning __________________ and hyperactivity.
4) Such __________________ is called variable expressivity.
e. The gene that codes for neurofibromatosis was discovered in __________________ to be on
chromosome 17.
1) The gene controls production of neurofibromin __________________ that normally blocks
growth signals for __________________
2) Many types of __________________ result in this effect.
3) Some mutations are caused by a __________________ that moves from another location in
the __________________.
2. Huntington Disease
a. This leads to progressive __________________ of brain cells, which in turn causes severe muscle
__________________, personality __________________, and death in __________________
years after onset.
b. Most appear __________________ until they are of __________________ and already have had
__________________ who might __________________ the gene; occasionally, first signs of the
disease are seen in __________________ or even younger.
c. The gene for Huntington disease is located on chromosome __________________
d. This gene contains many repeats of a base __________________ that codes for glutamine in the
huntingtin __________________; normal persons have 10–15 glutamines; affected persons have
36 or more.
e. A huntingtin protein with over 36 glutamines __________________ shape and forms large clumps
inside __________________; it also attracts other proteins to __________________ with it.
3. Achondroplasia
a. This disease is a common form of __________________, associated with a defect in the growth of
long bones.
b. Affected individuals have __________________ arms and legs, a sway __________________,
and a normal torso and __________________.
c. About 1 in 25,000 people have the __________________.
d. Individuals with the disease are __________________ (Aa); the homozygous recessive (aa)
condition yields __________________ -length limbs, while the homozygous
__________________ (AA) condition is __________________.
11.4 Beyond Mendelian Genetics
A. Incomplete Dominance
1. Incomplete dominance: offspring show traits __________________ between two parental
phenotypes.
a. __________________ red and white-flowered four-o’clocks produce pink-flowered offspring.
b. __________________ __________________ has a biochemical basis; the level of gene-directed
protein production may be between that of the __________________ homozygotes.
c. One allele of a __________________ pair only partially dominates expression of its partner.
d. This does not support a __________________ theory; parental phenotypes reappear in F2
generation.
B. Human Examples of Incomplete Dominance
1. Curly versus Straight Hair
a. A curly-haired Caucasian and a straight-haired Caucasian will have __________________ -haired
offspring.
b. Two wavy-haired parents will produce a 1:2:1 ratio of curly-wavy-straight hair children.
2. Sickle-cell disease, Tay Sachs disease, and cystic fibrosis are considered examples of
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__________________
C. Multiple Allelic Traits
1. This occurs when a gene has many allelic forms or __________________ expressions.
2. __________________ Blood Types
a. The ABO system of human blood types is a __________________ allele system.
b. Two __________________ alleles (IA and IB) code for presence of A and B glycoproteins on
__________________.
c. This also includes a __________________ allele (iO) coding for no A or B glycoproteins on red
blood cells.
d. As a result, there are __________________ possible phenotypes (blood types): A, B, AB, and O
e. This is a case of __________________, where both alleles are fully expressed.
3. The Rh factor is inherited independently from the ABO system; the Rh+ __________________ is
__________________.
D. Polygenic Inheritance
1. Polygenic inheritance occurs when __________________ trait is governed by __________________
or more sets of alleles.
2. __________________ alleles have a quantitative effect on the phenotype: each adds to the
__________________.
3. The more genes involved, the more __________________ is the variation in phenotypes, resulting in a
__________________.
4. Crosses of white and dark-red wheat seeds produce seeds with __________________ degrees of
__________________ colors due to genes at three separate loci.
5.
Human Examples of Polygenic Inheritance
a. A hybrid cross for __________________ color provides a range of intermediates.
b. Parents with intermediate skin color can produce children with the full range of
__________________
c. __________________, where one gene __________________ with the expression of others, is an
example of epistasis.
E. Polygenic Disorders
1. This includes __________________, clubfoot, congenital dislocations of the hip,
__________________, __________________, schizophrenia, allergies and __________________.
2. Behavioral traits including __________________, phobias, alcoholism, and homosexuality may be
__________________ with particular genes but are not likely completely __________________.
3. Environment and the Phenotype
a. In water buttercups, the aquatic environment dramatically __________________ the structure of
the plant.
b. __________________ triggers a primrose to develop white flowers when grown above 32 oC and
red flowers when grown at 24oC.
c. The coats of Siamese cats and Himalayan rabbits have __________________ tipped ears, nose,
paws, etc. due to the __________________ encoded by an allele which is only active at the
__________________ at low temperatures.
F. Environment and the Phenotype
1. Both genotype and the environment affect the __________________.
2. Water and temperature can have profound __________________ on the phenotype.
a. A flower might be one color at one __________________ and another color at another temperature.
b. The coat color of certain animals can change with __________________.
11:B Chromosomal Inheritance
1.
2.
_______________ are located on chromosomes; this is called the chromosome theory of inheritance.
Chromosomes can be categorized as two types:
a. _______________ are non-sex chromosomes that are the same number and kind between sexes.
b. _______________ determine if the individual is male or female.
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3.
4.
Sex chromosomes in the human female are _______; those of the male are ________.
Males produce ____-containing and _______-containing gametes; therefore males determine the
_____________of offspring.
5. Besides genes that determine sex, sex chromosomes carry many _______________ for traits unrelated
to _______________.
6. An _______________ is any gene located on X chromosome; used to describe genes on X
chromosome that are missing on the _________chromosome.
A. X-Linked Alleles
1. Work with fruit flies (Drosophila) by Thomas Hunt Morgan (early 1900s) confirmed genes were on
_______________.
a. Fruit flies are easily and inexpensively raised in common _______________ glassware.
b. Females only mate _______________ and lay hundreds of _______________.
c. The fruit fly generation time is _______________, allowing rapid experiments.
2. Fruit flies have an_______________ sex chromosome system similar to the human system;
experiments can be correlated to the _______________ situation.
a. Newly discovered mutant male fruit flies had _______________ eyes.
b. Cross of the hybrids from the white-eyed male crossed with a dominant red-eyed female yielded
the expected _______________ red-to-white ratio; however, all of the white-eyed flies were
_______________.
c. An allele for eye color on the X but not on the Y _______________ supports the results of this
cross.
d. Behavior of this allele corresponds to the behavior of the chromosome; this confirmed the
_____________________________________________.
3. X-Linked Problems
a. X-linked alleles are designated as superscripts to the ___________chromosome.
b. Heterozygous females are _______________; they do not show the trait but can transmit it.
c. Males are never carriers but express the one allele on the ____________chromosome; the allele
could be dominant or recessive.
d. One form of color-blindness is X-linked _______________.
B. Human X-Linked Disorders
1. More _______________ have X-linked traits because recessive alleles on the X chromosome in males
are _______________ in males.
2. Color Blindness
a. Color blindness can be an _______________ disorder involving mutations of genes coding for
green or red sensitive cone cells, resulting in the inability to perceive green or red, respectively;
the pigment for blue-sensitive protein is _______________.
b. About 8% of Caucasian men have red-green _______________.
3. Muscular Dystrophy
a. Duchenne muscular dystrophy is the most common form and is characterized by wasting away of
_______________, eventually leading to death; it affects one out of every 3,600
_______________ births.
b. This X-linked recessive disease involves a _______________ gene that fails to produce the
_______________ dystrophin.
c. Signs and symptoms (e.g., waddling gait, toe walking, frequent _______________, difficulty in
_______________) soon appear.
d. Muscles weaken until the individual is confined to a wheelchair; death usually occurs by age
_______________.
e. Affected males are _______________ fathers; the gene passes from carrier mother to
_______________ daughter.
f. Lack of dystrophin protein causes calcium ions to leak into _______________ cells; this promotes
action of an _______________ that dissolves muscle fibers.
g. As the body attempts to _______________ tissue, fibrous tissue forms and cuts off blood supply
to the affected _______________.
h. A test now detects carriers of Duchenne muscular dystrophy; _______________ are being
attempted.
3. Hemophilia
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a.
4.
About one in 10,000 males is a _______________ with impaired ability of blood to
_______________.
b. The two common types: Hemophilia A, due to the _______________ of clotting factor IX;
Hemophilia B, due to the absence of clotting factor VIII.
c. Hemophiliacs bleed _______________ after an injury and also suffer internal bleeding around
_______________.
d. Hemorrhages stop with _______________ of blood (or plasma) or concentrates of clotting protein.
e. Factor VIII is now available as a _______________ -engineered product.
f. Of Queen Victoria’s 26 offspring, _______________ grandsons had hemophilia and four
granddaughters were _______________.
Fragile X Syndrome (See Health and Focus box)
a. In this case, the X chromosome is nearly _______________; most often found in males.
b. This affects one in 1,500 _______________ and one in 2,500 females.
c. As children, they are often _______________ or autistic with delayed or repetitive speech.
d. As adults, males usually have _______________ testes, unusually protruding _______________,
and other symptoms.
e. About one-fifth of males with _______________ X do not show symptoms.
f. Fragile X passes from a symptomless female carrier to grandson.
g. It has been traced to excessive repeats of base triplet _______________ (cytosine-guanineguanine); up to 230 copies compared to normal 6–to–50 copies.
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