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Chapter 11 Complex Chapter 11 Complex Inheritance and Human Inheritance and Human

HeredityHeredity11.1 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 scientific Mendel’s work went unnoticed by the scientific

community for about 30 years then it was community for about 30 years then it was rediscovered in the early 1900s.rediscovered in the early 1900s.

At that time many scientists were interested in At that time many scientists were interested in the cause of diseases and noticed that some the cause of diseases and noticed that some diseases “ran in families”.diseases “ran in families”.

Alkaptonuria was the first identified (recessive) Alkaptonuria was the first identified (recessive) genetic disorder. Alkaptonuria, from an genetic disorder. Alkaptonuria, from an enzyme deficiency, causes black acidic urine enzyme deficiency, causes black acidic urine and later in life affects bones and joints.and later in life affects bones 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 matingrepresent mating

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 trait has a parent with the trait then this trait is then this trait is dominant. If non-affected dominant. If non-affected parents produce an parents produce an offspring with the trait 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