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PATTERNS OF HEREDITY AND
HUMAN GENETICS
MENDELIAN INHERITANCE OF
HUMAN TRAITS
CHAPTER 12.1: Objectives
• Interpret a pedigree.
• Identify human genetic disorders caused by
inherited recessive alleles.
• Predict how a human trait can be determined
by a simple dominant allele.
• A _______ ____traces a family name and
various family members through successive
generations.
• Through a family tree, you can identify the
relationships among your cousins, aunts,
uncles, grandparents, and greatgrandparents.
• A ________ is a graphic representation of
genetic inheritance.
• It is a ________ made up of a set of symbols
that identify ______ and _______,
individuals affected by the trait being
studied, and family relationships.
Male
Parents
Female
Siblings
Affected
male
Known
heterozygotes
for recessive
allele
Affected
female
Mating
Death
Female
I
Male
1
2
II
2
1
3
4
5
III
?
1
2
4
3
IV
1
2
3
4
5
• In a pedigree,
a _____
represents a
______; a
______
represents a
____.
I
1
2
II
3
2
1
4
5
III
?
2
1
4
3
IV
1
2
3
4
5
• Highlighted
circles and
squares represent
individuals
showing the ____
being studied.
I
1
2
II
2
1
3
4
5
III
?
1
2
4
3
IV
1
2
3
4
5
• Circles and
squares that are
___highlighted
designate
individuals that
do not show the
trait.
• A half-shaded
circle or square
represents a
________, a
___________
individual.
I
1
2
II
2
1
III
?
1
2
3
4
5
4
3
IV
1
2
3
4
5
• A _________ line
connecting a ____
and a ______
indicates that the
individuals are
parents, and a
_______ line
connects parents
with their
offspring.
I
1
2
II
1
III
?
IV
1
2
1
3
2
4
4
3
2
5
3
4
5
• Each horizontal
row of circles
and squares in a
pedigree
designates a
__________with
the most recent
generation
shown at the
bottom.
I
1
2
II
11
3
2
4
5
III
?
1
2
4
3
IV
1
2
3
4
5
• The generations
are identified in
sequence by
_____
________, and
each individual
is given an
______ number.
• Most genetic disorders are caused by
_____________ _______.
• _________ ______(__) is a fairly common
genetic disorder among white Americans.
• Approximately one in 28 white Americans
carries the recessive allele, and one in 2500
children born to white Americans inherits the
disorder.
• Due to a defective _______ in the ______
________, ______ ________ results in the
formation and accumulation of thick mucus
in the ______ and _________ tract.
• __________ (tay saks) disease is a recessive
disorder of the central nervous system.
• In this disorder, a recessive allele results in
the absence of an enzyme that normally
breaks down a ______ produced and stored
in tissues of the _______ ________ system.
I
1
2
II
1
III
2
3
4
1
2
3
IV
1
• _______________ (fen ul kee tun YOO ree uh),
also called (____), is a recessive disorder that
results from the absence of an enzyme that
converts one amino acid, phenylalanine, to a
different amino acid, _________.
• Because ____________ cannot be broken
down, it and its by-products accumulate in
the body and result in severe damage to the
_______ ________ system.
• A ___ test is normally performed on all
infants a few days after birth.
• Infants affected by PKU are given a diet that
is low in ____________ until their ______
are fully developed.
• Ironically, the success of treating
phenylketonuria infants has resulted
in a new problem.
• If a female who is __________ _______ for
PKU becomes pregnant, the high
phenylalanine levels in her blood can
damage her _____—the developing baby.
• This problem occurs even if the fetus is
_________ and would be ____________
normal.
Phenylketonurics: Contains _______________
• Many _____ are inherited just as the rule of
dominance predicts.
• Remember that in Mendelian inheritance, a
single _________ allele inherited from one
parent is all that is needed for a person to
show the dominant trait.
• A _____ ___,
widow’s peak
hairline, hitchhiker’s
thumb, almond
shaped eyes, thick
lips, and the presence
of hair on the middle
section of your
fingers all are
examples of _______
traits.
• _____________ is a lethal genetic disorder
caused by a rare dominant allele.
• It results in a breakdown of certain areas
of the _____.
• Ordinarily, a dominant allele with such
severe effects would result in _____ before
the affected individual could have children
and pass the allele on to the next generation.
• But because the onset of Huntington’s
disease usually occurs between the ages of
__ and __, an individual may already have
had children before knowing whether he or
she is affected.
Typical Pedigree of Huntington’s Disease
I
1
2
II
2
1
4
3
5
III
1
2
3
4
5
WHEN HEREDITY FOLLOWS
DIFFERENT RULES
CHAPTER 12.2: Objectives
• Distinguish between alleles for incomplete
dominance and codominance.
• Explain the patterns of multiple allelic and
polygenic inheritance.
• Analyze the pattern of sex-linked
inheritance.
• Summarize how internal and external
environments affect gene expression.
• Patterns of inheritance that are explained by
Mendel’s experiments are often referred to as
simple.
• However, many inheritance patterns are
more ________ than those studied by
Mendel.
• When inheritance follows a pattern of
_________, _________ and _______
dominant individuals both have the same
phenotype.
• When traits are inherited in an ________
__________pattern, however, the phenotype
of heterozygous individuals is ___________
between those of the two homozygotes.
• For example, if a homozygous red-flowered
snapdragon plant (__) is crossed with a
homozygous white-flowered snapdragon
plant (____), all of the F1 offspring will have
_____ ________.
Red
White
All
pink
Pink
(RR’)
Red
(RR)
White
(R’R’)
Pink
(RR’)
All pink flowers
1 red: 2 pink: 1 white
• The new ________ occurs because the
flowers contain enzymes that control
pigment production.
• The R allele codes for an enzyme that
produces a red pigment. The R’ allele codes
for a _________ enzyme that makes no
pigment.
• Because the heterozygote has only one copy
of the R allele, its flowers appear pink
because they produce only half the amount
of red pigment that red homozygote flowers
produce.
• ___________ _______cause the phenotypes
of both homozygotes to be produced in
heterozygous individuals.
• In ___________, both alleles are _________
equally.
• Although each _____ has only ___ alleles in
the patterns of heredity you have studied thus
far, it is common for more than two alleles to
control a trait in a population.
• Traits controlled by more than two alleles
have _________ ______.
• In humans the diploid number of chromosomes
is__, or _______.
• There are __ pairs of homologous chromosomes
called __________. Homologous autosomes
look alike.
• The ___ ____of chromosomes differs in males
and females.
• These two chromosomes, which determine
the sex of an individual, are called ___
______________ and are indicated by the
letters __ and __.
• If you are ______,
your 23rd pair of
chromosomes are
homologous, __.
X
Y
Male
X
X
Female
• If you are ____,
your 23rd pair of
chromosomes ___,
look different.
• Males usually have one __ and one __
chromosome and produce two kinds of
_______, X and Y.
• Females usually have ___ X chromosomes
and produce only X gametes.
• It is the male gamete that determines the
___ of the offspring.
XY
Male
X
X
XX
Female
Y
XX
Female
XY
Male
XX
Female
XY
Male
X
• Traits controlled by genes located on sex
chromosomes are called _______________.
• The alleles for sex-linked traits are written
as _________ of the X or Y chromosomes.
• Because the X and Y chromosomes are not
homologous, the Y chromosome has no
_____________ allele to one on the X
chromosome and no superscript is used.
• Also remember that any recessive allele on
the X chromosome of a male will not be
masked by a corresponding dominant allele
on the Y chromosome.
White-eyed
male (XrY)
F2
Females:
all red eyed
Redeyed
female
(XRXR)
Males:
1/2 red eyed
F1 All red eyed
1/2 white
eyed
• The genes that govern sex-linked traits
follow the inheritance pattern of the sex
chromosome on which they are found.
• ___________ ____is the inheritance pattern
of a trait that is controlled by two or more
genes.
• The genes may be on the same chromosome
or on different chromosomes, and each
gene may have two or more alleles.
• __________ and _________ letters are
used to represent the alleles.
• However, the allele represented by an
uppercase letter is not dominant. All
heterozygotes are intermediate in _________.
• In _________ inheritance, each allele
represented by an uppercase letter
contributes a small, but equal, portion to the
trait being expressed.
• The result is that the phenotypes usually
show a continuous range of variability from
the ________ value of the trait to the
___________ value.
• The genetic makeup of an organism at
__________ determines only the organism’s
potential to develop and function.
• As the organism develops, many ______ can
influence how the gene is expressed, or even
whether the gene is expressed at all.
• Two such influences are the organism’s
_________ and _________ environments.
• __________, nutrition, ______, chemicals,
and __________ agents all can influence
gene expression.
• In arctic foxes
temperature has
an effect on the
expression of
coat _____.
• External influences can also be seen in leaves.
______can have different sizes, __________,
and shapes depending on the amount of light
they receive.
• The internal
environments of males
and females are
different because of
_______ and structural
differences.
• An organism’s ___
can also affect gene
function.
COMPLEX INHERITANCE OF HUMAN
TRAITS
CHAPTER 12.3: Objectives
• Identify codominance, multiple allelic,
sex-linked and polygenic patterns of
inheritance in humans.
• Distinguish among conditions that result
from extra autosomal or sex chromosomes.
• Remember that in __________, the
phenotypes of both homozygotes are produced
in the heterozygote.
• One example of this in humans is a group of
inherited red blood cell disorders called
______________________.
• In an individual who is _________ for the
sickle-cell allele, the oxygen-carrying protein
____________ differs by one amino acid from
normal hemoglobin.
• This defective hemoglobin forms crystal-like
structures that change the shape of the red
blood cells. _______ red blood cells are discshaped, but ________ red blood cells are
shaped like a ______, or half-moon.
• The change in shape occurs in the body’s
narrow ___________ after the hemoglobin
delivers _______ to the cells.
Normal red
blood cell
Sickle cell
• Abnormally shaped blood cells, _____ blood
flow, _____ small vessels, and result in _____
damage and pain.
Normal red
blood cell
Sickle cell
• Individuals who are heterozygous for the
allele produce both normal and sickled
hemoglobin, an example of ___________.
• Individuals who are _________ are said to
have the sickle-cell trait because they can
show some signs of sickle-cell-related
disorders if the availability of _______ is
reduced.
• Mendel’s laws of heredity also can be applied
to traits that have more than two alleles.
• The ____ blood group is a classic example
of a single gene that has multiple alleles in
humans.
Human Blood Types
Genotypes
lA lA or lAli
lB lB or lBi
lA lB
ii
Surface Molecules
A
B
A and B
None
Phenotypes
A
B
AB
O
• Determining _____ type is necessary before a
person can receive a blood ___________
because the red blood cells of incompatible
blood types could ______ together, causing
death.
• The gene for blood type, gene l, codes for a
_______ that attaches to a _________ protein
found on the surface of red blood cells.
• The __ and __ alleles each code for a
different molecule.
• Your ______ system recognizes the red blood
cells as belonging to you. If cells with a
different _______ molecule enters your body,
your immune system will attack them.
Surface molecule A
• The __ allele is
dominant to __, so
inheriting either the
___ alleles or the
____ alleles from
both parents will give
you ______blood.
• Surface molecule __
is produced.
• The __ allele is also
dominant to __.
• To have type __ blood,
you must inherit the __
allele from one parent
and either another __
allele or the __ allele
from the other.
• Surface molecule __ is
produced.
Surface molecule B
Surface molecule B
• The __and __alleles
are ____________.
• This means that if you
inherit the __ allele from
one parent and the __
allele from the other,
your red blood cells will
produce both surface
molecules and you will
have _____ ___blood.
Surface molecule A
• The __ allele is
_________ and
produces no surface
molecules.
• Therefore, if you
are homozygous __,
your blood cells
have __ surface
molecules and you
have blood ______.
• Many human traits are determined by genes
that are carried on the sex chromosomes;
most of these genes are located on the
__chromosome.
• The pattern of _______________________
is explained by the fact that males, who are
XY, pass an X chromosome to each daughter
and a Y chromosome to each son.
• Females, who are XX, pass one of their X
chromosomes to each child.
Male
Female
Female
Sperm
Eggs
Eggs
Female
Female
Male
Male
Female
Male
Sperm
Male
Female
Male
• If a son receives an __ chromosome with a
recessive allele, the recessive ________ will
be expressed because he does not inherit on
the __ chromosome from his father a
dominant allele that would ____ the
expression of the recessive allele.
• Two traits that are governed by X-linked
recessive inheritance in humans are
______________________and __________.
• People who have redgreen color blindness
can’t differentiate these
two colors. Color
blindness is caused by
the inheritance of a
recessive allele at either
of two gene sites on the
__ chromosome.
• ______________is an X-linked disorder that
causes a problem with blood clotting.
• About one ____ in every 10,000 has
hemophilia, but only about one in 100
million _______ inherits the same disorder.
• Males inherit the allele for hemophilia on the
__ chromosome from their carrier mothers.
One recessive allele for __________ will
cause the disorder in males.
• Females would need ___ __________ alleles
to inherit hemophilia.
• Although many of your traits were inherited
through simple Mendelian patterns or through
multiple alleles, many other human traits are
determined by polygenic inheritance.
• In the early 1900s, the idea that
________________occurs in humans was
first tested using data collected on skin
color.
• Scientists found that when light-skinned
people mate with dark-skinned people, their
offspring have ___________ skin colors.
Number of individuals
Number of Genes Involved in Skin Color
Expected
distribution4 genes
Observed
distribution
of skin
color
Light
Expected
distribution1 gene
Range of skin color
Expected
distribution3 genes
Right
• This graph
shows the
expected
distribution of
human skin
color if
controlled by
one, three, or
four genes.
• What would happen if an entire chromosome
or part of a chromosome were missing from
the complete set?
• As you have learned, ___________ numbers
of chromosomes in offspring usually, but not
always, result from accidents of _______.
• Many abnormal ____________ effects result
from such mistakes.
• Humans who have an extra whole or partial
autosome are ________—that is, they have
three of a particular autosomal chromosome
instead of just two. In other words, they have
__ _________________.
• To identify an abnormal number of
chromosomes, a sample of cells is obtained
from an individual or from a fetus.
• __________ chromosomes are photographed;
the chromosome pictures are then enlarged
and arranged in pairs by a computer
according to length and location of the
____________.
• This chart of chromosome pairs is called a
___________, and it is valuable in identifying
unusual chromosome numbers in cells.
• ____ _________is
the only autosomal
_______ in which
affected
individuals survive
to adulthood.
• It occurs in about
one in 700 live
births.
• Down syndrome is a group of symptoms that
results from trisomy of ____________ __.
• Individuals who have Down syndrome have
at least some _______ of mental retardation.
• The incidence of Down syndrome births is
higher in _____ mothers, especially those
over 40.
• Many abnormalities in the number of sex
chromosomes are known to exist.
• An X chromosome may be missing
(designated as __) or there may be an extra
one (___ or ____). There may also be an
extra Y chromosome (____).
• Any individual with at least one Y
chromosome is a ____, and any individual
without a Y chromosome is a _______.
• Most of these individuals lead normal lives,
but they ______ have children and some have
varying degrees of mental retardation.