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Title: BDOL Interactive Chalkboard


1

2
Table of Contents pages iv-v
Unit 1 What is Biology? Unit 2 Ecology Unit
3 The Life of a Cell Unit 4 Genetics Unit 5
Change Through Time Unit 6 Viruses, Bacteria,
Protists, and Fungi Unit 7 Plants Unit 8
Invertebrates Unit 9 Vertebrates Unit 10 The
Human Body
3
Table of Contents pages iv-v
Unit 1 What is Biology? Chapter 1
Biology The Study of Life Unit 2 Ecology
Chapter 2 Principles of Ecology Chapter
3 Communities and Biomes Chapter 4
Population Biology Chapter 5 Biological
Diversity and Conservation Unit 3 The Life of a
Cell Chapter 6 The Chemistry of Life
Chapter 7 A View of the Cell Chapter 8
Cellular Transport and the Cell Cycle
Chapter 9 Energy in a Cell
4
Table of Contents pages iv-v
Unit 4 Genetics Chapter 10 Mendel and
Meiosis Chapter 11 DNA and Genes
Chapter 12 Patterns of Heredity and Human
Genetics Chapter 13 Genetic Technology Unit
5 Change Through Time Chapter 14 The
History of Life Chapter 15 The Theory of
Evolution Chapter 16 Primate Evolution
Chapter 17 Organizing Lifes Diversity
5
Table of Contents pages iv-v
Unit 6 Viruses, Bacteria, Protists, and Fungi
Chapter 18 Viruses and Bacteria Chapter
19 Protists Chapter 20 Fungi Unit 7
Plants Chapter 21 What Is a Plant?
Chapter 22 The Diversity of Plants
Chapter 23 Plant Structure and Function
Chapter 24 Reproduction in Plants
6
Table of Contents pages iv-v
Unit 8 Invertebrates Chapter 25 What Is
an Animal? Chapter 26 Sponges,
Cnidarians, Flatworms, and
Roundworms Chapter 27
Mollusks and Segmented Worms Chapter 28
Arthropods Chapter 29 Echinoderms and
Invertebrate
Chordates
7
Table of Contents pages iv-v
Unit 9 Vertebrates Chapter 30 Fishes
and Amphibians Chapter 31 Reptiles and
Birds Chapter 32 Mammals Chapter 33
Animal Behavior Unit 10 The Human Body
Chapter 34 Protection, Support, and
Locomotion Chapter 35 The Digestive and
Endocrine Systems Chapter 36 The Nervous
System Chapter 37 Respiration,
Circulation, and Excretion Chapter 38
Reproduction and Development Chapter 39
Immunity from Disease
8
Unit Overview pages 250-251
Genetics
Mendel and Meiosis
DNA and Genes
Patterns of Heredity and Human Genetics
Genetic Technology
9
Chapter Contents page viii
Chapter 12 Patterns of Heredity and Human
Genetics 12.1 Mendelian Inheritance of
Human Traits 12.1 Section Check 12.2 When
Heredity Follows Different Rules 12.2 Section
Check 12.3 Complex Inheritance of Human
Traits 12.3 Section Check Chapter 12
Summary Chapter 12 Assessment
10
Chapter Intro-page 308
What Youll Learn
You will compare the inheritance of recessive and
dominant traits in humans.
You will analyze the inheritance patterns of
traits with incomplete dominance and codominance.
You will determine the inheritance of sex-linked
traits.
11
12.1 Section Objectives page 309
Section 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.

12
Section 12.1 Summary pages 309 - 314
Making a Pedigree
  • A family tree 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 great-grandparents.

13
Section 12.1 Summary pages 309 - 314
Pedigrees illustrate inheritance
  • A pedigree is a graphic representation of genetic
    inheritance.
  • It is a diagram made up of a set of symbols that
    identify males and females, individuals affected
    by the trait being studied, and family
    relationships.

14
Section 12.1 Summary pages 309 - 314
Male
Parents
Siblings
Female
Pedigrees illustrate inheritance
Affected male
Known heterozygotes for recessive allele
Affected female
Mating
Death
15
Section 12.1 Summary pages 309 - 314
Pedigrees illustrate inheritance
Female
Male
I
1
2
II
2
1
3
4
5
  • In a pedigree, a circle represents a female a
    square represents a male.

III
1
4
2
3
?
IV
5
3
4
2
1
16
Section 12.1 Summary pages 309 - 314
Pedigrees illustrate inheritance
I
1
2
II
3
2
1
4
5
  • Highlighted circles and squares represent
    individuals showing the trait being studied.

III
1
4
2
3
?
IV
2
3
5
1
4
17
Section 12.1 Summary pages 309 - 314
Pedigrees illustrate inheritance
I
1
2
II
  • Circles and squares that are not highlighted
    designate individuals that do not show the trait.

2
3
1
4
5
III
1
4
2
3
?
IV
3
5
2
4
1
18
Section 12.1 Summary pages 309 - 314
Pedigrees illustrate inheritance
  • A half-shaded circle or square represents a
    carrier, a heterozygous individual.

19
Section 12.1 Summary pages 309 - 314
Pedigrees illustrate inheritance
  • A horizontal line connecting a circle and a
    square indicates that the individuals are
    parents, and a vertical line connects parents
    with their offspring.

I
1
2
II
4
3
2
1
5
III
1
4
2
3
?
IV
2
3
5
1
4
20
Section 12.1 Summary pages 309 - 314
Pedigrees illustrate inheritance
  • Each horizontal row of circles and squares in a
    pedigree designates a generation, with the most
    recent generation shown at the bottom.

I
1
2
II
1
3
2
4
5
III
1
2
4
3
?
IV
3
5
1
2
4
21
Section 12.1 Summary pages 309 - 314
Pedigrees illustrate inheritance
  • The generations are identified in sequence by
    Roman numerals, and each individual is given an
    Arabic number.

I
1
2
II
1
3
2
4
5
III
1
2
4
3
?
IV
3
5
1
2
4
22
Section 12.1 Summary pages 309 - 314
Simple Recessive Heredity
  • Most genetic disorders are caused by recessive
    alleles.

Cystic fibrosis
  • Cystic fibrosis (CF) is a fairly common genetic
    disorder among white Americans.

23
Section 12.1 Summary pages 309 - 314
Cystic fibrosis
  • 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 protein in the plasma
    membrane, cystic fibrosis results in the
    formation and accumulation of thick mucus in the
    lungs and digestive tract.

24
Section 12.1 Summary pages 309 - 314
Tay-Sachs disease
  • Tay-Sachs (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 lipid produced and stored in tissues of
    the central nervous system.
  • Because this lipid fails to break down properly,
    it accumulates in the cells.

25
Section 12.1 Summary pages 309 - 314
I
1
2
Typical Pedigree for
II
1
2
3
4
Tay-Sachs
III
3
1
2
IV
1
26
Section 12.1 Summary pages 309 - 314
Phenylketonuria
  • Phenylketonuria (fen ul kee tun YOO ree uh), also
    called (PKU), is a recessive disorder that
    results from the absence of an enzyme that
    converts one amino acid, phenylalanine, to a
    different amino acid, tyrosine.
  • Because phenylalanine cannot be broken down, it
    and its by-products accumulate in the body and
    result in severe damage to the central nervous
    system.

27
Section 12.1 Summary pages 309 - 314
Phenylketonuria
  • A PKU test is normally performed on all infants a
    few days after birth.
  • Infants affected by PKU are given a diet that is
    low in phenylalanine until their brains are fully
    developed.
  • Ironically, the success of treating
    phenylketonuria infants has resulted in a new
    problem.

28
Section 12.1 Summary pages 309 - 314
Phenylketonuria
  • If a female who is homozygous recessive for PKU
    becomes pregnant, the high phenylalanine levels
    in her blood can damage her fetusthe developing
    baby.
  • This problem occurs even if the fetus is
    heterozygous and would be phenotypically normal.

29
Section 12.1 Summary pages 309 - 314
Phenylketonuria
Phenylketonurics Contains Phenylalanine
30
Section 12.1 Summary pages 309 - 314
Simple Dominant Heredity
  • Many traits are inherited just as the rule of
    dominance predicts.
  • Remember that in Mendelian inheritance, a single
    dominant allele inherited from one parent is all
    that is needed for a person to show the dominant
    trait.

31
Section 12.1 Summary pages 309 - 314
Simple dominant traits
  • A cleft chin, widows peak hairline, hitchhikers
    thumb, almond shaped eyes, thick lips, and the
    presence of hair on the middle section of your
    fingers all are examples of dominant traits.

32
Section 12.1 Summary pages 309 - 314
Huntingtons disease
  • Huntingtons disease is a lethal genetic disorder
    caused by a rare dominant allele.
  • It results in a breakdown of certain areas of the
    brain.

33
Section 12.1 Summary pages 309 - 314
Huntingtons disease
  • Ordinarily, a dominant allele with such severe
    effects would result in death before the affected
    individual could have children and pass the
    allele on to the next generation.
  • But because the onset of Huntingtons disease
    usually occurs between the ages of 30 and 50, an
    individual may already have had children before
    knowing whether he or she is affected.

34
Section 12.1 Summary pages 309 - 314
Typical Pedigree of Huntingtons Disease
I
1
2
II
1
2
5
4
3
III
1
2
3
4
5
35
Section 1 Check
Question 1
I
1
2
What does this pedigree tell you about
those who show the recessive phenotype for the
disease?
II
1
2
3
4
III
3
1
2
IV
1
36
Section 1 Check
I
The pedigree indicates that showing the recessive
phenotype for the disease is fatal.
1
2
II
1
2
3
4
III
3
1
2
IV
1
37
Section 1 Check
Question 2
What must happen for a person to show a
recessive phenotype?
Answer
The person must inherit a recessive allele for
the trait from both parents.
38
Section 1 Check
Question 3
Which of the following diseases is the
result of a dominant allele?
A. Huntingtons disease
B. Tay-Sachs disease
C. cystic fibrosis
D. phenylketonuria
The answer is A.
39
12.2 Section Objectives page 315
Section 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.

40
Section 12.2 Summary pages 315 - 322
Complex Patterns of Inheritance
  • Patterns of inheritance that are explained by
    Mendels experiments are often referred to as
    simple.
  • However, many inheritance patterns are more
    complex than those studied by Mendel.

41
Section 12.2 Summary pages 315 - 322
Incomplete dominance Appearance of a third
phenotype
  • When inheritance follows a pattern of dominance,
    heterozygous and homozygous dominant individuals
    both have the same phenotype.
  • When traits are inherited in an incomplete
    dominance pattern, however, the phenotype of
    heterozygous individuals is intermediate between
    those of the two homozygotes.

42
Section 12.2 Summary pages 315 - 322
Incomplete dominance Appearance of a third
phenotype
  • For example, if a homozygous red-flowered
    snapdragon plant (RR) is crossed with a
    homozygous white-flowered snapdragon plant (R'
    R'), all of the F1 offspring will have pink
    flowers.

43
Section 12.2 Summary pages 315 - 322
Incomplete dominance Appearance of a third
phenotype
Red
White
All pink
Red (RR)
Pink (RR)
White (RR)
Pink (RR)
All pink flowers
1 red 2 pink 1 white
44
Section 12.2 Summary pages 315 - 322
Incomplete dominance Appearance of a third
phenotype
  • The new phenotype 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 defective
    enzyme that makes no pigment.

45
Section 12.2 Summary pages 315 - 322
Incomplete dominance Appearance of a third
phenotype
  • 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.

46
Section 12.2 Summary pages 315 - 322
Incomplete dominance Appearance of a third
phenotype
Red
White
All pink
Red (RR)
Pink (RR)
White (RR)
Pink (RR)
All pink flowers
1 red 2 pink 1 white
47
Section 12.2 Summary pages 315 - 322
Codominance Expression of both alleles
  • Codominant alleles cause the phenotypes of both
    homozygotes to be produced in heterozygous
    individuals. In codominance, both alleles are
    expressed equally.

48
Section 12.2 Summary pages 315 - 322
Multiple phenotypes from multiple alleles
  • Although each trait has only two 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
    multiple alleles.

49
Section 12.2 Summary pages 315 - 322
Sex determination
  • In humans the diploid number of chromosomes is
    46, or 23 pairs.
  • There are 22 pairs of homologous chromosomes
    called autosomes. Homologous autosomes look
    alike.
  • The 23rd pair of chromosomes differs in males and
    females.

50
Section 12.2 Summary pages 315 - 322
Sex determination
  • These two chromosomes, which determine the sex of
    an individual, are called sex chromosomes and are
    indicated by the letters X and Y.

51
Section 12.2 Summary pages 315 - 322
Sex determination
  • If you are female, your 23rd pair of chromosomes
    are homologous, XX.

X
X
Female
  • If you are male, your 23rd pair of chromosomes
    XY, look different.

Y
X
Male
52
Section 12.2 Summary pages 315 - 322
Sex determination
  • Males usually have one X and one Y chromosome and
    produce two kinds of gametes, X and Y.
  • Females usually have two X chromosomes and
    produce only X gametes.
  • It is the male gamete that determines the sex of
    the offspring.

53
Section 12.2 Summary pages 315 - 322
XY Male
Sex determination
X
Y
X
XX Female
XY Male
XX Female
X
XY Male
XX Female
54
Section 12.2 Summary pages 315 - 322
Sex-linked inheritance
  • Traits controlled by genes located on sex
    chromosomes are called sex-linked traits.
  • The alleles for sex-linked traits are written as
    superscripts of the X or Y chromosomes.
  • Because the X and Y chromosomes are not
    homologous, the Y chromosome has no corresponding
    allele to one on the X chromosome and no
    superscript is used.

55
Section 12.2 Summary pages 315 - 322
Sex-linked inheritance
  • 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.

56
Section 12.2 Summary pages 315 - 322
Sex-linked inheritance
White-eyed male (XrY)
F2
Females
Red-eyed female (XRXR)
all red eyed
Males
1/2 red eyed
1/2 white eyed
F1 All red eyed
57
Section 12.2 Summary pages 315 - 322
Sex-linked inheritance
  • The genes that govern sex-linked traits follow
    the inheritance pattern of the sex chromosome on
    which they are found.

Click here to view movie.
58
Section 12.2 Summary pages 315 - 322
Polygenic inheritance
  • Polygenic inheritance 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.
  • Uppercase and lowercase letters are used to
    represent the alleles.

59
Section 12.2 Summary pages 315 - 322
Polygenic inheritance
  • However, the allele represented by an uppercase
    letter is not dominant. All heterozygotes are
    intermediate in phenotype.
  • In polygenic inheritance, each allele represented
    by an uppercase letter contributes a small, but
    equal, portion to the trait being expressed.

60
Section 12.2 Summary pages 315 - 322
Polygenic inheritance
  • The result is that the phenotypes usually show a
    continuous range of variability from the minimum
    value of the trait to the maximum value.

61
Section 12.2 Summary pages 315 - 322
Environmental Influences
  • The genetic makeup of an organism at
    fertilization determines only the organisms
    potential to develop and function.
  • As the organism develops, many factors can
    influence how the gene is expressed, or even
    whether the gene is expressed at all.
  • Two such influences are the organisms external
    and internal environments.

62
Section 12.2 Summary pages 315 - 322
Influence of external environment
  • Temperature, nutrition, light, chemicals, and
    infectious agents all can influence gene
    expression.

63
Section 12.2 Summary pages 315 - 322
Influence of external environment
  • In arctic foxes temperature has an effect on the
    expression of coat color.

64
Section 12.2 Summary pages 315 - 322
Influence of external environment
  • External influences can also be seen in leaves.
    Leaves can have different sizes, thicknesses, and
    shapes depending on the amount of light they
    receive.

65
Section 12.2 Summary pages 315 - 322
Influence of internal environment
  • The internal environments of males and females
    are different because of hormones and structural
    differences.
  • An organisms age can also affect gene function.

66
Section 2 Check
Question 1
What is the difference between simple
Mendelian inheritance and codominant inheritance?
67
Section 2 Check
In Mendelian inheritance, heterozygous
individuals will display the inherited dominant
trait of the homozygotes. When traits are
inherited in a codominant pattern the phenotypes
of both homozygotes are displayed equally in the
heterozygotes.
68
Section 2 Check
Question 2
Which of the following does NOT have an
effect on male-pattern baldness?
A. hormones
B. internal environment
C. sex-linked inheritance
D. incomplete dominance
The answer is D.
69
Section 2 Check
Question 3
If the offspring of human mating have a
50-50 chance of being either male or female, why
is the ratio not exactly 11 in a small
population?
Answer
The ratio is not exactly 11 because the laws of
probability govern fertilization.
70
12.3 Section Objectives page 323
Section 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.

71
Section 12.3 Summary pages 323 - 329
Codominance in Humans
  • Remember that in codominance, 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
    sickle-cell disease.

72
Section 12.3 Summary pages 323 - 329
Sickle-cell disease
  • In an individual who is homozygous for the
    sickle-cell allele, the oxygen-carrying protein
    hemoglobin differs by one amino acid from normal
    hemoglobin.
  • This defective hemoglobin forms crystal-like
    structures that change the shape of the red blood
    cells. Normal red blood cells are disc-shaped,
    but abnormal red blood cells are shaped like a
    sickle, or half-moon.

73
Section 12.3 Summary pages 323 - 329
Sickle-cell disease
  • The change in shape occurs in the bodys narrow
    capillaries after the hemoglobin delivers oxygen
    to the cells.

Normal red blood cell
Sickle cell
74
Section 12.3 Summary pages 323 - 329
Sickle-cell disease
  • Abnormally shaped blood cells, slow blood flow,
    block small vessels, and result in tissue damage
    and pain.

Normal red blood cell
Sickle cell
75
Section 12.3 Summary pages 323 - 329
Sickle-cell disease
  • Individuals who are heterozygous for the allele
    produce both normal and sickled hemoglobin, an
    example of codominance.
  • Individuals who are heterozygous are said to have
    the sickle-cell trait because they can show some
    signs of sickle-cell-related disorders if the
    availability of oxygen is reduced.

76
Section 12.3 Summary pages 323 - 329
Multiple Alleles Govern Blood Type
  • Mendels laws of heredity also can be applied to
    traits that have more than two alleles.
  • The ABO blood group is a classic example of a
    single gene that has multiple alleles in humans.

77
Section 12.3 Summary pages 323 - 329
Multiple Alleles Govern Blood Type
Human Blood Types
Genotypes
Surface Molecules
Phenotypes
A
A
lA lA or lAli
B
B
lB lB or lBi
lA lB
A and B
AB
None
ii
O
78
Section 12.3 Summary pages 323 - 329
The importance of blood typing
  • Determining blood type is necessary before a
    person can receive a blood transfusion because
    the red blood cells of incompatible blood types
    could clump together, causing death.

79
Section 12.3 Summary pages 323 - 329
The ABO Blood Group
  • The gene for blood type, gene l, codes for a
    molecule that attaches to a membrane protein
    found on the surface of red blood cells.
  • The lA and lB alleles each code for a different
    molecule.
  • Your immune system recognizes the red blood cells
    as belonging to you. If cells with a different
    surface molecule enter your body, your immune
    system will attack them.

80
Section 12.3 Summary pages 323 - 329
Phenotype A
Surface molecule A
  • The lA allele is dominant to i, so inheriting
    either the lAi alleles or the lA lA alleles from
    both parents will give you type A blood.
  • Surface molecule A is produced.

81
Section 12.3 Summary pages 323 - 329
Phenotype B
Surface molecule B
  • The lB allele is also dominant to i.
  • To have type B blood, you must inherit the lB
    allele from one parent and either another lB
    allele or the i allele from the other.
  • Surface molecule B is produced.

82
Section 12.3 Summary pages 323 - 329
Phenotype AB
Surface molecule B
  • The lA and lB alleles are codominant.
  • This means that if you inherit the lA allele from
    one parent and the lB allele from the other, your
    red blood cells will produce both surface
    molecules and you will have type AB blood.

Surface molecule A
83
Section 12.3 Summary pages 323 - 329
Phenotype O
  • The i allele is recessive and produces no surface
    molecules.
  • Therefore, if you are homozygous ii, your blood
    cells have no surface molecules and you have
    blood type O.

84
Section 12.3 Summary pages 323 - 329
Sex-Linked Traits in Humans
  • Many human traits are determined by genes that
    are carried on the sex chromosomes most of these
    genes are located on the X chromosome.
  • The pattern of sex-linked inheritance is
    explained by the fact that males, who are XY,
    pass an X chromosome to each daughter and a Y
    chromosome to each son.

85
Section 12.3 Summary pages 323 - 329
Sex-Linked Traits in Humans
  • Females, who are XX, pass one of their X
    chromosomes to each child.

Female
Male
Male
Female
Sperm
Eggs
Eggs
Sperm
Male
Male
Female
Female
Female
Female
Male
Male
86
Section 12.3 Summary pages 323 - 329
Sex-Linked Traits in Humans
  • If a son receives an X chromosome with a
    recessive allele, the recessive phenotype will be
    expressed because he does not inherit on the Y
    chromosome from his father a dominant allele that
    would mask the expression of the recessive allele.
  • Two traits that are governed by X-linked
    recessive inheritance in humans are red-green
    color blindness and hemophilia.

87
Section 12.3 Summary pages 323 - 329
Red-green color blindness
  • People who have red-green color blindness cant
    differentiate these two colors. Color blindness
    is caused by the inheritance of a recessive
    allele at either of two gene sites on the X
    chromosome.

88
Section 12.3 Summary pages 323 - 329
Hemophilia An X-linked disorder
  • Hemophilia A is an X-linked disorder that causes
    a problem with blood clotting.
  • About one male in every 10 000 has hemophilia,
    but only about one in 100 million females
    inherits the same disorder.

89
Section 12.3 Summary pages 323 - 329
Hemophilia An X-linked disorder
  • Males inherit the allele for hemophilia on the X
    chromosome from their carrier mothers. One
    recessive allele for hemophilia will cause the
    disorder in males.
  • Females would need two recessive alleles to
    inherit hemophilia.

90
Section 12.3 Summary pages 323 - 329
Polygenic Inheritance in Humans
  • Although many of your traits were inherited
    through simple Mendelian patterns or through
    multiple alleles, many other human traits are
    determined by polygenic inheritance.

91
Section 12.3 Summary pages 323 - 329
Skin color A polygenic trait
  • In the early 1900s, the idea that polygenic
    inheritance 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 intermediate skin colors.

92
Section 12.3 Summary pages 323 - 329
Skin color A polygenic trait
  • This graph shows the expected distribution of
    human skin color if controlled by one, three, or
    four genes.

Number of Genes Involved in Skin Color
Expected distribution- 4 genes
Observed distribution of skin color
Expected distribution- 1 gene
Number of individuals
Expected distribution- 3 genes
Light
Right
Range of skin color
93
Section 12.3 Summary pages 323 - 329
Changes in Chromosome Numbers
  • What would happen if an entire chromosome or part
    of a chromosome were missing from the complete
    set?
  • As you have learned, abnormal numbers of
    chromosomes in offspring usually, but not always,
    result from accidents of meiosis.
  • Many abnormal phenotypic effects result from such
    mistakes.

94
Section 12.3 Summary pages 323 - 329
Abnormal numbers of autosomes
  • Humans who have an extra whole or partial
    autosome are trisomicthat is, they have three of
    a particular autosomal chromosome instead of just
    two. In other words, they have 47 chromosomes.
  • To identify an abnormal number of chromosomes, a
    sample of cells is obtained from an individual or
    from a fetus.

95
Section 12.3 Summary pages 323 - 329
Abnormal numbers of autosomes
  • Metaphase chromosomes are photographed the
    chromosome pictures are then enlarged and
    arranged in pairs by a computer according to
    length and location of the centromere.

96
Section 12.3 Summary pages 323 - 329
Abnormal numbers of autosomes
  • This chart of chromosome pairs is called a
    karyotype, and it is valuable in identifying
    unusual chromosome numbers in cells.

97
Section 12.3 Summary pages 323 - 329
Down syndrome Trisomy 21
  • Down syndrome is the only autosomal trisomy in
    which affected individuals survive to adulthood.
  • It occurs in about one in 700 live births.

98
Section 12.3 Summary pages 323 - 329
Down syndrome Trisomy 21
  • Down syndrome is a group of symptoms that results
    from trisomy of chromosome 21.
  • Individuals who have Down syndrome have at least
    some degree of mental retardation.
  • The incidence of Down syndrome births is higher
    in older mothers, especially those over 40.

99
Section 12.3 Summary pages 323 - 329
Abnormal numbers of sex chromosomes
  • Many abnormalities in the number of sex
    chromosomes are known to exist.
  • An X chromosome may be missing (designated as XO)
    or there may be an extra one (XXX or XXY). There
    may also be an extra Y chromosome (XYY).

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Section 12.3 Summary pages 323 - 329
Abnormal numbers of sex chromosomes
  • Any individual with at least one Y chromosome is
    a male, and any individual without a Y chromosome
    is a female.
  • Most of these individuals lead normal lives, but
    they cannot have children and some have varying
    degrees of mental retardation.

101
Section 3 Check
Question 1
Which of the following inherited diseases
would a black American be most likely to
inherit? (TX Obj 2 6C)
A. cystic fibrosis
B. Tay-Sachs disease
C. phenylketonuria
D. sickle-cell disease
The answer is D.
102
Section 3 Check
Question 2
Trisomy usually results from _______. (TX
Obj 2 6C)
A. polygenic inheritance
B. incomplete dominance
C. nondisjunction
D. twenty-two pairs of chromosomes
The answer is C.
103
Section 3 Check
Question 3
How do red blood cells of phenotype O
differ from the cells of the other phenotypes?
Answer
Red blood cells of phenotype O display no surface
molecules.
104
Chapter Summary 12.1
Mendelian Inheritance of Human Traits
  • A pedigree is a family tree of inheritance.
  • Most human genetic disorders are inherited as
    rare recessive alleles, but a few are inherited
    as dominant alleles.

105
Chapter Summary 12.2
When Heredity Follows Different Rules
  • Some alleles can be expressed as incomplete
    dominance or codominance.
  • There may be many alleles for one trait or many
    genes that interact to produce a trait.
  • Cells have matching pairs of homologous
    chromosomes called autosomes.
  • Sex chromosomes contain genes that determine the
    sex of an individual.

106
Chapter Summary 12.2
When Heredity Follows Different Rules
  • Inheritance patterns of genes located on sex
    chromosomes are due to differences in the number
    and kind of sex chromosomes in males and in
    females.
  • The expression of some traits is affected by the
    internal and external environments of the
    organism.

107
Chapter Summary 12.3
Complex Inheritance of Human Traits
  • The majority of human traits are controlled by
    multiple alleles or by polygenic inheritance.
    The inheritance patterns of these traits are
    highly variable.
  • Sex-linked traits are determined by inheritance
    of sex chromosomes. X-linked traits are usually
    passed from carrier females to their male
    offspring. Y-linked traits are passed only from
    male to male.

108
Chapter Summary 12.3
Complex Inheritance of Human Traits
  • Nondisjunction may result in an abnormal number
    of chromosomes. Abnormal numbers of autosomes
    usually are lethal.
  • A karyotype can identify unusual numbers of
    chromosomes in an individual.

109
Chapter Assessment
Question 1
Which of the following is NOT a sex-linked trait?
(TX Obj 2 6C)
A. hemophilia
B. sickle-cell disease
C. male patterned baldness
D. red-green color blindness
The answer is B.
110
Chapter Assessment
Question 2
Human eye color is determined by _______.
A. the influence of hormones
B. sex-linked inheritance
C. codominance
D. polygenic inheritance
The answer is D.
111
Chapter Assessment
Question 3
What are blood phenotypes based on?
Answer
Blood phenotypes are based on a molecule that
attaches to a membrane protein found on the
surface of red blood cells.
112
Chapter Assessment
Question 4
Cob length in corn is the result of _______.
A. sex-linked inheritance
B. incomplete dominance
C. polygenic inheritance
D. simple dominance
The answer is C.
113
Chapter Assessment
Question 5
A cleft chin is the result of _______.
A. simple dominance
B. incomplete dominance
C. polygenic inheritance
D. sex-linked inheritance
The answer is A.
114
Chapter Assessment
Question 6
What is the difference between simple Mendelian
inheritance and inheritance by incomplete
dominance?
115
Chapter Assessment
In Mendelian inheritance, heterozygous
individuals will display the inherited dominant
trait of the homozygotes. However, when traits
are inherited in an incomplete dominance pattern,
the phenotype of heterozygous individuals is
intermediate between those of the two homozygotes.
116
Chapter Assessment
Question 7
If a trait is Y-linked, males pass the Y-linked
allele to _______ of their daughters.
A. a quarter
B. half
C. all
D. none
117
Chapter Assessment
The answer is D. Y-linked traits are only passed
to males.
118
Chapter Assessment
Question 8
What is necessary for a person to show a dominant
trait?
Answer
The person must inherit at least a single
dominant allele from one parent for the trait to
appear.
119
Chapter Assessment
Question 9
Why is sickle-cell disease considered to be an
example of codominant inheritance?
Answer
Individuals who are heterozygous for the
sickle-cell allele produce both normal and
sickled hemoglobin. This is an example of
codominance.
120
Chapter Assessment
Question 10
What sex is an XXY individual?
Answer
Any individual with at least one Y chromosome is
a male.
121
Chapter Assessment
Photo Credits
  • Aaron Haupt
  • Digital Stock
  • Horizons Companies
  • Russ Lappa
  • Scott Cunningham
  • Alton Biggs

122
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