Genetics

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Genetics
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Essential Question

• How do chromosomes get passed from one generation
  to the next?

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Genetics

• Genetics? the scientific study of heredity
• Gregor MendelAustrian monk
• Father of Genetics

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Must know terms

• Traitspecific characteristic varies from one
  individual to another example height
• Hybridoffspring of crosses between parents with
  different traits
• Dominantexpressed trait
• Recessivenon expressed trait present only in
  the absence of the dominant

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Must know terms

• Homozygousindividuals with two identical alleles
  for a particular trait true breeding
• Heterozygousindividuals with two different
  alleles for a particular traithybrid
• PhenotypePhysical characteristics
• GenotypeGenetic makeup

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Must know terms

• AlleleDifferent forms of a gene
• P generationParental generation
• F1 generationfirst generation after P
• F2 generationsecond generation after P
• Probabilityis the likelihood that a particular
  event will occur

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Monohybrid cross

• Mating of two individuals either homozygous or
  heterozygous
• Capital letters represent dominant traits
• Lower case letters represent recessive traits
• For heterozygous crosses ratio is 31 dominant to
  recessive

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Practice Problems
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Practice Problems
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Practice Problems
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Practice Problems
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Practice Problems
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Monohybrid Crosses

• In pea plants, spherical seeds (S) are dominant
  to dented seeds (s). In a genetic cross of two
  plants that are heterozygous for the seed shape
  trait, what fraction of the offspring should have
  spherical seeds?

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Monohybrid Crosses

• In a pea plants, tall plants (T) are dominant to
  short plants (t). In a genetic cross between two
  plants that are heterozygous for height, what
  fraction of the offspring should be short? What
  fraction of the offspring should be tall?

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Monohybrid Crosses

• In dogs, wire hair (S) is dominant to smooth (s).
  In a cross of a homozygous wire-haired dog with a
  smooth-haired dog, what will be the phenotype of
  the F1 generation

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Monohybrid Crosses

• In woodrats let's assume that the trait of
  bringing home shiny objects (H) is controlled by
  a single gene and is dominant to the trait of
  carrying home only dull objects (h). Suppose two
  heterozygous individuals are crossed. How many of
  each genotype would be expected if only 4
  offspring were produced?

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Monohybrid Crosses

• The ability to curl your tongue up on the sides
  (T, tongue rolling) is dominant to not being able
  to roll your tongue. A woman who can roll her
  tongue marries a man who cannot. Their first
  child has his father's phenotype. What are the
  genotypes of the mother, father, and child?

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Dihybrid Crosses

• Cross in which two hybrids are mated to test for
  dominant genes and recessive genes in two
  separate characteristics.
• For heterozygous crosses the ratio is 9331

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Dihybrid Crosses

• Wolves are sometimes observed to have black coats
  and blue eyes. Assume that normal coat color (N)
  is dominant to black (n) and brown eyes (B) are
  dominant to blue (b). Suppose the alpha male and
  alpha female of a pack (these are the dominant
  individuals who do most of the breeding) are
  black with blue eyes and normal colored with
  brown eyes, respectively. The female is also
  heterozygous for both traits. How many of the
  offspring (assume 16) living in the pack will
  have each of the following genotypes?

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Practice Problems
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Dihybrid Crosses

• Suppose that anoles prefer to mate with lizards
  who bob their heads fast (F) and have red throat
  patches (R) and that these two alleles are
  dominant to their counterparts, slow bobbing and
  yellow throats. A male lizard heterozygous for
  head bobbing and homozygous dominant for the red
  throat patch mates with a female that is also
  heterozygous for head bobbing but is homozygous
  recessive for yellow throat patches. How many of
  the F1 offspring have the preferred fast bobbing
  / red throat phenotype (assume 16 young)?

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Practice Problems
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Dihybrid Crosses

• Carrion beetles lay their eggs in dead animals
  and then bury them in the ground until they
  hatch. Assume that the preference for fresh meat
  (F) is dominant to the preference for rotted meat
  and that the tendency to bury the meat shallow
  (S) is dominant to the tendency to bury the meat
  deep. Suppose a female carrion beetle homozygous
  dominant for both traits mates with a male
  homozygous recessive for both traits. What will
  be the genotype of the F1 generation?

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Practice Problems