Chapter 11 Complex Inheritance and Human Heredity

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Chapter 11 Complex Inheritance and Human Heredity

• 11.1 Basic Patterns of Human Inheritance

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Recessive Genetic Disorders

• Mendels work went unnoticed by the scientific
  community for about 30 years then it was
  rediscovered in the early 1900s.
• At that time many scientists were interested in
  the cause of diseases and noticed that some
  diseases ran in families.
• Alkaptonuria was the first identified (recessive)
  genetic disorder. Alkaptonuria, from an enzyme
  deficiency, causes black acidic urine and later
  in life affects bones and joints.

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Recessive 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 2

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Dominant Genetic Disorders
99.9 of population is homozygous recessive for
achondroplasia
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Huntingtons Disease

• Affects the nervous system
• Latent disorder affects age 30 to 50
• Gradual loss of brain function (holes in brain)
• Genetic test available
• Result of allele mutation at tip of chromosome 4

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Achondroplasia

• Most common form of dwarfism
• 75 of individuals born to parents of average
  size, result of new mutation
• Lethal spontaneous abortion in homozygous
  dominant genotype

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Pedigree Analysis
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Pedigree Analysis

• Are females
• Are males
• Shaded in circles and squares are affected
  individuals
• Roman Numerals (I IV) are generations
• Lines across represent mating
• Lines down represent offspring

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Pedigree Analysis

• Count the number of affected males and affected
  females. If most males and few or no females
  most likely sex linked trait.
• Look at the affected individuals. If every
  individual with the trait has a parent with the
  trait then this trait is dominant. If
  non-affected parents produce an offspring with
  the trait then it is recessive.
• Determine the phenotype and genotype of every
  individual

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Pedigree Analysis

• Count the number of affected males and affected
  females. If most males and few or no females
  most likely sex linked trait.
• Look at the affected individuals. If every
  individual with the trait has a parent with the
  trait then this trait is dominant. If
  non-affected parents produce an offspring with
  the trait then it is recessive.
• Determine the phenotype and genotype of every
  individual

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Pedigree Analysis

• Affected males 1
• Affected females 2 (not sex linked)
• No affected individual has parent with the trait,
  means recessive
• All affected individuals would be homozygous
  recessive, aa
• All parents of affected individuals would be
  heterozygous, Aa
• Siblings of affected individuals would be
  heterozygous (Aa) or homozygous dominant (AA)

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Pedigree Analysis
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Chapter 11 Complex Inheritance and Human Heredity

• 11.2 Complex Patterns of Inheritance

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Incomplete Dominance

• Many scientists repeated Mendels work expecting
  to get similar results with different species.
  Carl Correns crossed white snapdragons with red
  snapdragons
• According to Mendelian genetics, results would
  have yielded 100 dominant phenotype (red or
  white)
• Correns found 100 pink

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Incomplete Dominance

• Incomplete Dominance is the appearance of an
  intermediate phenotype
• Both alleles are expressed producing both the red
  and white proteins which gives the appearance of
  pink

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Codominance

• Both phenotypes of the two homozygotes are
  expressed
• See red and white (not pink)

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Codominance

• Both phenotypes of the two homozygotes are
  expressed
• See red hairs and white hairs (not pink)

Roan Cattle
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Codominance

• Sickle cell disease most common genetic disorder
  in African Americans (1 in 400).
• In heterozygous condition both normal (round) and
  sickle red blood cells are produced
• Few disease symptoms in heterozygous individual

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Codominance

• Sickle cells do not effectively carry oxygen,
  cause blockage in blood vessels, pain and
  fatigue.
• Heterozygous condition protects against malaria
  (see p.303)

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Multiple Alleles

• More than two alleles
• Human blood groups have three alleles ABO
• Blood Types Genotypes
• A IA IA or IAi
• B IB IB or IBi
• AB IA IB
• O ii
• Both IA and IB are dominant to i and are
  codominant to each other

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Multiple Alleles

• Multiple alleles can demonstrate a hierarchy of
  dominance.
• In rabbits, four alleles code for coat color C,
  cch, ch, and c.
• C is dominant to cch, ch, and c.
• cch is dominant to ch and c.
• ch is dominant to c.
• c is recessive to all

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Multiple Alleles
Chinchilla
?
Albino
Light gray
Dark gray
Himalayan
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Epistasis

• Variety is the result of one allele hiding the
  effects of another allele.

eebb
eeB_
E_bb
E_B_
No dark pigment present in fur
Dark pigment present in fur
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Sex Determination

• Sex chromosomes determine an individuals gender.
  
• Human males are XY females XX
• Autosomes are the nonsex chromosomes
• Humans have 22 pairs of autosomes

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Dosage Compensation

• The X chromosome is more than three times larger
  than the Y chromosome has more than three times
  more information
• Females (XX) have two copies of this information
  while males (XY) have only one copy of the X
  chromosome
• In females one of the X chromosomes stops
  working which X is a random event and becomes a
  Barr Body

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Dosage Compensation

• Barr bodies form from the inactivated extra X
  chromosome in females
• Colors of the calico cat are caused by the random
  inactivation of a particular X chromosome (orange
  on one X and black on the other X chromosome)

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Sex-Linked Traits

• The X and Y chromosomes are not homologous (do
  not pair carry different information)
• Males only have one X chromosome only one allele
  for each trait only need one recessive to show
  the trait
• Males show the sex linked traits much more often
  than females

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Sex-Linked Traits

• Red Green Color Blindness
• 8 of United States males affected
• Red and green colors look like shades of brown
• Are you color blind?

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Sex-Linked Traits

• Hemophilia is characterized by delayed blood
  clotting.
• Common in Royal Families of Europe due to
  intermarriage

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Polygenic Traits

• Poly many genic genes
• Many genes needed to determine a trait
• Most human traits are polygenic

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Environmental Influences

• Environment has an influence on phenotype
• Sunlight without enough sunlight most flowering
  plants do not bear flowers
• Water many plants lose their leaves in response
  to lack of water.
• others diet, exercise

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Environmental Influences

• Temperature Siamese cats tail, feet, ears and
  nose are dark in response to cooler temperatures
  the black pigment production is responsive to
  temperature

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Twin Studies

• Helps scientists separate genetic contributions
  from environmental contributions

• Traits that appear frequently in identical twins
  are at least partially controlled by heredity.

• Traits expressed differently in identical twins
  are strongly influenced by environment.
• Interesting information from identical twins
  separated at birth in Minnesota Twin Studies

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Chapter 11 Complex Inheritance and Human Heredity

• 11.3 Chromosomes and Human Heredity

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Karyotype Studies

• Karyotype is a micrograph (picture) of
  chromosomes at metaphase arranged by size in
  homologous pairs.
• Twenty-two pairs of autosomes are the same for
  males and females.
• Males have one X chromosome and one Y chromosome
  (not paired) and females have two X chromosomes
  (paired).
• Karyotypes are useful for detecting chromosome
  abnormalities

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Karyotype Studies
Chromosome smear
Karyotype
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Telomeres

• Telomeres protective end caps on the chromosomes
  made of DNA and proteins.
• Short repetitive nonessential DNA sequences
• Prevent one chromosome form binding to another
  chromosome (not sticky)

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Telomeres

• Absolutely essential for chromosome function
• Telomeres decrease in size (length) as an
  organism ages and may play a role in aging and
  cancer.
• Cancer cells have increased length of telomeres
  compared to adult cells.
• Telomere function is an intense field of research

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Nondisjunction

• Failure of chromosomes to separate during cell
  division
• Results in one cell getting too many chromosomes
  and one cell not getting enough.
• If nondisjunction occurs during meiosis the
  resulting gametes could form an organism with
  every cell having an incorrect chromosome number.

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Down Syndrome

• Results of parental gamete nondisjunction
  resulting in trisomy (three chromosomes ) of
  chromosome 21.
• Symptoms include mental retardation, distinctive
  facial features, short stature, heart defects,
  sexually underdeveloped, sterile, more likely to
  develop leukemia and Alzheimer's, shorter life
  span

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Down Syndrome
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Down Syndrome

• Incidence of Down Syndrome increases with
  increasing age of the mother
• Risk increases to 6 for mothers over age 45
• Recommended fetal testing for mothers age 35 and
  older

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Other Trisomys

• Patau syndrome trisomy 13 1/5000 serious eye,
  brain and circulatory problems lifespan less
  than 1 year
• Edwards syndrome trisomy 18 1/10,000 effects
  every body organ lifespan less than 1 year

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Nondisjunction of Sex Chromosomes Male

• Klinefelter syndrome (XXY) 1/2000 males sex
  organs, testes abnormally small sterile
  feminine body characteristics (breast
  enlargement, fat deposition) normal intelligence
• (XYY) taller than average male not
  characterized by a syndrome some suggest
  increased aggression

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Nondisjunction of Sex Chromosomes Female

• (XXX) 1/1000 normal due to X inactivitation
  only distinguishable by karyotype
• Turner syndrome Monosomy X (XO) 1/5000 female
  with no maturation of sex organs no secondary
  sex characteristics short sterile normal
  intelligence with spatial learning disabilities

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Fetal Testing

• Amniocentesis removal amniotic fluid with
  sloughed fetal cells at 14th -16th week for
  diagnosis of chromosomal abnormalities 1 risk
  of complications

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Fetal Testing

• Chorionic villus sampling removal of placental
  sample at 8th -10th week quicker results less
  accurate less than 1 risk of complications

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Fetal Testing

• Fetal blood sampling sample of fetal blood can
  detect increased number of genetic abnormalities
  medication can be given to fetus before birth
  greater risk to fetus