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PowerPoint Lecture Outlines
to accompany
Hole’s Human
Anatomy and Physiology
Eleventh Edition
Shier w Butler w Lewis
Chapter
24
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
1
Chapter 24
Genetics and Genomics
Genetics – study of inheritance of characteristics
Genome – complete set of genetic instructions
Genomics – field in which the body is studied in terms of
multiple, interacting genes
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From Gene to Protein:
Cystic Fibrosis
• when the gene
coding for CFTR
protein is mutant,
cystic fibrosis results
• CFTR protein folds
into a channel that
regulates the flow of
Cl- into and out of
cells lining the
respiratory tract,
pancreas, and
elsewhere
3
From Protein to Person:
Cystic Fibrosis
• when CFTR is
abnormal, it traps
Cl- in cells
• water in cells
forms very thick
mucus
4
Chromosomes and Genes Come in
Pairs
23 pairs of chromosomes
• pairs 1-22 are autosomes
• pair 23 are sex chromosomes
Normal karyotype
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Genotype and Phenotype
Genotype
• particular combination of genes
• alleles are variant forms of the same gene
• homozygous – identical alleles
• heterozygous – different alleles
• wild type allele – produces most common or normal
phenotype
Phenotype
• way that genes are expressed
• blue eyes, presence of a protein, etc
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Dominant and Recessive
Inheritance
Dominant allele masks the phenotype of the recessive allele
Recessive allele is expressed only if in a double dose (homozygous)
Autosomal conditions are carried on a nonsex chromosome
Sex-linked conditions are carried on a sex chromosome
X-linked conditions are carried on the X chromosome
Y-linked conditions are carried on the Y chromosome
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Autosomal Recessive Disorder
• cystic fibrosis is an
example
• sexes are affected with
equal frequencies
• offspring probabilities
• 25% homozygous
dominant
• 50% heterozygous
• 25% homozygous
recessive
• punnet square and a
pedigree are useful ways
to express genetic
information
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Autosomal Dominant Disorder
• Huntington
disease is an
example
• a person with one
HD allele develops
the disease
• both sexes are
equally affected
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Different Dominance Relationships:
Incomplete Dominance
• heterozygote has a
phenotype
intermediate between
homozygous
dominant and
homozygous recessive
• familial
hypercholesterolemia
is an example
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Different Dominance Relationships:
Codominance
• different alleles are both expressed
• ABO blood type is an example
• three alleles of ABO blood typing are IA, IB, I
• a person with type A may have the genotype IA i or IA IA
• a person with type B may have the genotype IB i or IB IB
• a person with type AB must have the genotype IA IB
• a person with type O blood must have the genotype ii
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Gene Expression:
Penetrance and Expressivity
Complete penetrance
• everyone who inherits the disease causing alleles
has some symptoms
Imcomplete penetrance
• some individuals do not express the phenotype
even though they inherit the alleles (example
polydactyly)
Variable expression
• symptoms vary in intensity in different people
• two extra digits versus three extra digits in
polydactyly
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Gene Expression:
Pleiotrophy and Genetic
Heterogeneity
Pleiotropy
• single genetic disorder producing several symptoms
• Marfan syndrome is an example
• people affected produce several symptoms that vary
Genetic Heterogeneity
• same phenotype resulting from the actions of different
genes
• hereditary deafness is an example
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Complex Traits
Most if not all characteristics and disorders considered
“inherited” actually reflect input from the environment
as well as genes.
Polygenic traits
• determined by more than one gene
• height, skin color, eye color
Multifactorial traits
• traits molded by one or more genes plus
environmental factors
• height and skin color
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Variations in Height
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Variations in Skin Color
Mid-range colors are more common
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Variations in Eye Color
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Sex Determination
• an egg contributes
an X chromosome
• a sperm contributes
either an X or a Y
chromosome
• A gene on the Y
chromosome, SRY,
determines sex
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Sex Chromosomes and Their
Genes
X chromosome
• has over 1,500 genes
• most genes on the X chromosome do not have
corresponding alleles on the Y chromosome
Y chromosome
• has only 231 protein-encoding genes
• some genes are unique only to the Y chromosome
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Sex-linked Genes
• Y-linked genes are transmitted only from father to son
• X-linked genes are transmitted from father to daughter
or from mother to daughter or son
• Hemophilia A is a sex-linked disorder
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Hemophilia A
• passed from mother (heterozygote) to son
• each son has a 50% chance of receiving the recessive allele from the
mother
• each son with one recessive allele will have the disease
• each son has no allele on the Y chromosome to mask the recessive allele
• each daughter has a 50% chance of receiving the recessive allele from the
mother
• each daughter with one recessive allele will be a carrier
• each daughter with one recessive allele does not develop the disease
because she has another X chromosome with a dominant allele
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Gender Effects on Phenotype
Sex-limited trait
• affects a structure or function of the body that
is present in only males or only females
• examples are beards or growth of breasts
Sex-influenced inheritance
• an allele is dominant in one sex and recessive in the
other
• baldness is an example
• heterozygous males are bald but heterozygous females
are not
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Chromosomal Disorders
Polyploidy
• extra set of chromosomes
• most embryos die
Aneuploidy
• missing a chromosome or having an extra chromosome
• results from nondisjunction
• trisomy is the condition of having an extra chromosome
• monosomy is the condition of missing a chromosome
Euploid is a normal chromosome number
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Causes of Aneuploidy
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Prenatal Tests
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Prenatal Tests
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Gene Therapy
• group of experimental techniques that alter, replace, silence,
or augment a gene’s function to improve, delay or prevent
symptoms
• heritable gene therapy
• introduces the genetic change into a sperm, egg, or
zygote
• changes passed to future generations
• common in plants; not done in humans
• nonheritable gene therapy
• targets only affected cells
• changes not passed to future generations
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Gene Therapy Targets
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Clinical Application
Down Syndrome
• most common autosomal aneuploid
• trisomy 21
• signs and symptoms include
• short stature
• mental retardation
• protruding tongue
• heart defects
• kidney defects
• suppressed immune systems
• digestive disorders
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