Non-Mendelian Genetics:

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Non-Mendelian Genetics
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Vocabulary Terms

• 89. Pedigree
• 90. Sex-linked trait
• 91. Polygenic trait
• 92. Incomplete dominance
• 93. Codominance
• 94. Multiple alleles
• 95. mutation

Read 171-180
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Chromosomes and Human Genetics

• Human Chromosomes
• Types
• Sex Chromosomes 1 pair carry the genes that
  determine male and female features (also some
  non-sex traits)
• X and Y do not look alike but behave as a
  homologous pair at meiosis
• XX female, XY male
• Autosomes non-sex chromosomes (22 pairs)
  genes are unrelated to sex determination

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B. Determining Sex
MOM
X
X
X
X
X
X
X
DAD
X
Y
X
Y
Y
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II. Gene Location

• Linked Linkage Groups genes located so close
  together on a chromosome that the traits always
  seem to appear together
• Ex. Red hair and freckles
• Ex. Colorblindness and Hemophilia

X X
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• Sex-linked Traits genes on the sex chromosomes
• Expression of certain genes often appears more in
  one sex than the other
• Males require only one copy of a gene since they
  only have one X chromosome
• See Royal Families of Europe Pedigree
• Ex. Eye color in fruit flies, hemophilia,
  color-blindness

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Colorblindness Tests
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X-Linked/Sex Linkage do not write

• Genes present on the X chromosome exhibit unique
  patterns of inheritance due to the presence of
  only one X chromosome in males.
• X-linked disorders show up rarely in females
• X linked disorders show up in males whose mothers
  were carriers (heterozygotes)

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Practice Sex-linked Problems.

• What will the result of mating between a normal
  (non-carrier) female and a hemophiliac male?

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• A female carrier who is heterozygous for the
  recessive, sex-linked trait causing red-green
  colorblindness, marries a normal male. What
  proportions of their MALE progeny will have
  red-green colorblindness?

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• Hemophilia is inherited as an X-linked recessive.
  A woman has a brother with this defect and a
  mother and father who are phenotypically normal.
  What is the probability that this woman will be a
  carrier if she herself is phenotypically normal?

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• Hemophilia is inherited as an X-linked recessive.
  
• A man with Hemophilia has several children with a
  woman who has a normal phenotype and is NOT a
  carrier. What of the children have hemophilia?
  What are carriers?

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C. Gene Interactions

1. Polygenetic trait many genes influence a single
   trait (ex. Height, intelligence)
2. Pleiotropic effect one gene having many effects
   (ex. Gene to make testosterone)

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Pleiotropy
?

• Expression of a single gene has multiple
  phenotypic effects
• Marfan Syndrome abnormal gene that makes
  fibrillin (important in connective tissues)

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III. Genetic Analysis

• Karyotype visualized chromosomes stained,
  squashed, and photographed at metaphase
• - They are characteristic of the species or
  individual

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B. Pedigree chart showing family relationships
(see worksheet)
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Pedigree Analysis

• Method of tracking a trait through generations
  within a family.
• Good method of tracking sex-linked traits as well
  as autosomal traits.

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Sex-Linked Pedigree

• Shows gender bias with males exhibiting the trait
  more often than females

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Autosomal Dominant Pedigree

• Autosomal dominant traits do not skip a
  generation
• Autosomal dominant traits do not show gender bias

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Autosomal Recessive Pedigree

• Autosomal recessive traits skip a generation
• Autosomal recessive traits do not show gender bias

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IV. Non-Mendelian Genetics

• Incomplete Dominance blended inheritance
• Neither form of the gene is able to mask the
  other
• Ex. Snap dragon petal color
• R1R1 RED
• R1R2 PINK
• R2R2 - WHITE

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Incomplete Dominance

• Neither allele is dominant
• Heterozygotes are a blend of homozygous
  phenotypes no distinct expression of either
  allele

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Try these

• In a plant species, if the B1 allele (blue
  flowers) and the B2 allele (white flowers) are
  incompletely dominant (B1 B2 is light blue), what
  offspring ratio is expected in a cross between a
  blue-flowered plant and a white-flowered plant?

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• What would be the phenotypic ratio of the flowers
  produced by a cross between two light blue
  flowers?

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2. Codominance

• No dominance and both alleles are completely
  expressed
• Ex. Cat color
• C1C1 Tan
• C1C2 Tabby (black and tan spotted)
• C2C2 - Black

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Try These

• Cattle can be red (RR all red hairs), white (WW
  all white hairs), or roan (RW red white
  hairs together.
• Predict the phenotypic ratios of offspring when a
  homozygous white cow is crossed with a roan bull.
  

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• What should the genotypes phenotypes for parent
  cattle be if a farmer wanted only cattle with red
  fur?

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• A cross between a black cat a tan cat produces
  a tabby pattern (black tan fur together).
• What pattern of inheritance does this illustrate?
  
• What percent of kittens would have tan fur if a
  tabby cat is crossed with a black cat?

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3. Multiple Alleles

• More than 2 alleles for one trait
• Ex. Eye color, hair color, blood type, guinea pig
  fur color
• ABO blood groups
• Each individual is A, B, AB, or O phenotype
• Phenotype controlled by marker on RBC
• IA and IB alleles are dominant to the i allele
• IA and IB alleles are codominant to each other

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Blood Types

• Blood Type
• A
• B
• AB
• O

• Genotype
• IAIA , IAi
• IBIB , IBi
• IAIB
• ii

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Try These

1. If a male is homozygous for blood type B and a
   female is heterozygous for blood type A, what are
   the possible blood types in the offspring?

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1. Is it possible for a child with Type O blood to
   be born to a mother who is type AB? Why or why
   not?

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1. A child is type AB. His biological mother is
   also type AB. What are the possible phenotypes
   of his biological father?

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V. Genetic Conditions

• Genetic Abnormality rare condition with little
  or no ill effects
• - Ex. Six fingers, albino, colorblindness

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2. Genetic Disorders

• Inherited condition that results in a medical
  problem
• - Ex. Huntingtons Disease, Sickle Cell Anemia,
  Hemophilia, Muscular Dystrophy

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3. Genetic Disease

• A genetic condition that makes the individual
  susceptible to infection (bacterial or viral)
• - Ex. Cystic fibrosis, Down syndrome, SCID
  (severe combined immunodeficiency disease
  bubble boy)

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VI. Mutations

• Definition any change in the DNA
• Possible outcomes good, bad, or no effect
• Location
• Somatic Cell (body cell) can lead to cancer
• Sex Cell reproductive organ effecting gametes

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Observed vs. Expected Ratios

• Observed Ratio what you actually get from two
  organisms having offspring all girls
• Expected Ratio based on your punnett square
  results what you would expect to get half
  girls and half boys
• Example using dice

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Human Genetics Test Topics

• Sex-linked Traits
• Incomplete Dominance/ Codominance
• Multiple Alleles (blood typing problems)
• Genetic Conditions
• Sex Chromosomes vs. Autosomes
• Pedigrees/Karyotypes
• Observed vs. Expected Ratios
• LOTS OF GENETICS PROBLEMS SHOW WORK!!!

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Human Genetics Test Review Questions

• My daughter is type A, my grandson is type B.
  What are the blood type(s) that the father would
  have to be in order for my grandson to be type B?
  

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• Red-green color blindness is X-linked in humans.
• If a male is red-green color blind, and both
  parents have normal color vision, which of the
  male's grandparents is most likely to be
  red-green color blind?
• A. maternal grandmother
• B. maternal grandfather
• C. paternal grandmother
• D. paternal grandfather
• E. either grandfather is
  equally likely

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• Suppose a child is of blood type A and the mother
  is of type 0. What type or types may the father
  belong to?

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• Suppose a father and mother claim they have been
  given the wrong baby at the hospital. Both
  parents are blood type A. The baby they have been
  given is blood type O. What evidence bearing on
  this case does this fact have?

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• Hemophilia is a sex-linked recessive trait. Cross
  a hemophiliac female with a normal male. Of all
  their offspring, what is the probability they
  will produce a hemophiliac daughter? (H normal
  blood, h hemophilia)

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• A man with Type A blood marries a woman with Type
  B blood. They have a type O child. What is the
  probability of their 15th child having type O
  blood?

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• A man whose father is type B and whose mother is
  type A, has a blood type of A. He marries a type
  A woman, whose parents had the same blood types
  as his parents. What are the genotypes of the
  man and the woman and what is the probability
  that their first child will be blood type A?

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• Coat color in cats is a codominant trait. Cats
  can be black, yellow or calico. A calico cat has
  black and yellow splotches. In order to be
  calico. the cat must have an allele for the black
  color and an allele for the yellow color. Show a
  cross between a calico cat and a yellow cat.
  What are the possible genotypes and phenotypes of
  the offspring?

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• A mother and father with normal color vision
  produce six male children, two of whom exhibit
  red-green colorblindness. Their five female
  children exhibit normal color vision. Ignoring
  the fact that these parents ought to seek some
  family planning advice, explain the inheritance
  of red-green colorblindness in their male
  children.

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A nurse at a hospital removed the wrist tags of
three babies in the maternity ward. She needs to
figure out which baby belongs to which parents,
so she checks their blood types. Using the chart
below, match the baby to its correct parents.
Show the crosses to prove your choices
Parents Blood Types Baby Blood type
Mr. Hartzel O    
Mrs. Hartzel A Jennifer O
Mr. Simon AB Rebecca A
Mrs. Simon AB Holly B
Mr. Peach O
Mrs. Peach O
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