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Chapter 11 Complex Chapter 11 Complex Inheritance and Human Inheritance and Human
HeredityHeredity
11.1 Basic Patterns of Human 11.1 Basic Patterns of Human InheritanceInheritance
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Recessive Genetic DisordersRecessive Genetic Disorders Mendel’s work went unnoticed by the Mendel’s work went unnoticed by the
scientific community for about 30 years then scientific community for about 30 years then it was rediscovered in the early 1900s.it was rediscovered in the early 1900s.
At that time many scientists were interested At that time many scientists were interested in the cause of diseases and noticed that in the cause of diseases and noticed that some diseases “ran in families”.some diseases “ran in families”.
Alkaptonuria was the first identified Alkaptonuria was the first identified (recessive) genetic disorder. Alkaptonuria, (recessive) genetic disorder. Alkaptonuria, from an enzyme deficiency, causes black from an enzyme deficiency, causes black acidic urine and later in life affects bones acidic urine and later in life affects bones and joints.and joints.
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Recessive Genetic DisordersRecessive Genetic Disorders A recessive trait is
expressed when the individual is homozygous recessive for the trait.
Both parents would need to have at least one recessive allele.
Usually the parents are heterozygous (carriers) for the disorder.
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Cystic Fibrosis
Affects the mucus-producing glands, digestive enzymes, and sweat glands
Chloride ions are not absorbed into the cells of a person with cystic fibrosis but are excreted in the sweat.
Without sufficient chloride ions in the cells, a thick mucus is secreted
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Cystic Fibrosis
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Cystic Fibrosis
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Albinism
Caused by altered genes, resulting in the absence of the skin pigment melanin in hair and eyes
White hair. Very pale skin Pink pupils
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Albinism
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Tay-Sachs Disease
Caused by the absence of the enzymes responsible for breaking down fatty acids called gangliosides
Gangliosides accumulate in the brain, inflating brain nerve cells and causing mental deterioration.
Death by age 2Death by age 2
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Dominant Genetic DisordersDominant Genetic Disorders
99.9% of population is homozygous recessive for achondroplasia
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Huntington’s DiseaseHuntington’s Disease Affects the nervous Affects the nervous
systemsystem Latent disorder Latent disorder
affects age 30 to 50affects age 30 to 50 Gradual loss of Gradual loss of
brain function brain function (“holes” in brain)(“holes” in brain)
Genetic test Genetic test availableavailable
Result of allele Result of allele mutation at tip of mutation at tip of chromosome #4chromosome #4
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AchondroplasiaAchondroplasia
Most common form Most common form of dwarfismof dwarfism
75% of individuals 75% of individuals born to parents of born to parents of average size, result average size, result of new mutationof new mutation
Lethal spontaneous Lethal spontaneous abortion in abortion in homozygous homozygous dominant genotypedominant genotype
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Pedigree AnalysisPedigree Analysis
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Pedigree AnalysisPedigree Analysis Are femalesAre females
Are malesAre males Shaded in circles and Shaded in circles and
squares are affected squares are affected individualsindividuals
Roman Numerals (Roman Numerals (I – I – IVIV) are generations) are generations
Lines across Lines across represent represent
matingmating Lines down Lines down
represent offspringrepresent offspring
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Pedigree AnalysisPedigree Analysis Count the number of Count the number of
affected males and affected males and affected females. If most affected females. If most males and few or no males and few or no females most likely sex females most likely sex linked trait.linked trait.
Look at the affected Look at the affected individuals. If every individuals. If every individual with the trait individual with the trait has a parent with the has a parent with the trait then this trait is trait then this trait is dominant. If non-dominant. If non-affected parents produce affected parents produce an offspring with the trait an offspring with the trait then it is recessive.then it is recessive.
Determine the phenotype Determine the phenotype and genotype of every and genotype of every individualindividual
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Pedigree AnalysisPedigree Analysis Affected males: 1 Affected males: 1 Affected females: 2 (not Affected females: 2 (not
sex linked)sex linked) No affected individual No affected individual
has parent with the trait, has parent with the trait, means recessivemeans recessive
All affected individuals All affected individuals would be homozygous would be homozygous recessive, aarecessive, aa
All parents of affected All parents of affected individuals would be individuals would be heterozygous, Aaheterozygous, Aa
Siblings of affected Siblings of affected individuals would be individuals would be heterozygous (Aa) or heterozygous (Aa) or homozygous dominant homozygous dominant (AA)(AA)
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Pedigree AnalysisPedigree Analysis