11-3 Exploring Mendelian Genetics

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11-3 Exploring Mendelian Genetics
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Independent Assortment

• The two- factor Cross F1
• The two- factor Cross F2

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The two- factor Cross F1

• Mendel crossed true- breeeding plants that
  produces only round yellow peas (Genotype RRYY)
  with plants that produces wrinkled green peas
  (Genotype rryy)

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The two- factor Cross F1

• Offspring produces round yellow peas.

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The two- factor Cross F1

• It provides hybrids plants needed for the next
  cross the F1 plants to produce the F2
  generation.

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How is the genotype of the offspring different
from the homozygous dominant parent?
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The two- factor Cross F2

• How would the alleles segregate when the F1
  plants were crossed to each other to produce an
  F2 generation?
• Each plant in the F1 generation was formed by the
  fusion of a gamete carrying the dominant RY
  allele with another gamete carrying the recessive
  ry alleles.
• Would they segregate independently so that any
  combination of alleles was possible?

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• It produced 556 seeds.
• In a variation of
• 315 were round and yellow
• 32 were wrinkle and green
• 209 with other combinations of alleles not found
  in parents.

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Independent Assortment

• Genes that segregate independently genes for
  seed shape and seed color in pea plants do not
  influence each others inheritance.

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The principle of independent assortment states
that genes for different traits can segregate
independently during the formation of gametes.
Independent assortment helps account for the many
genetic variations observed in plants, animals,
and other organisms.
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A summary of Mendels Principles

• The inheritance of biological characteristics is
  determined by individual unit known as genes.
  Genes are passed from parents to their offspring.
• In cases in which two or more forms (alleles) of
  the gene for a single trait exist, some forms of
  the gene may be dominant and other may be
  recessive.

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A summary of Mendels Principles (2)

• In most sexually reproducing organisms, each
  adult has two copies of each gene one from each
  parent. These genes are segregate from each other
  when gametes are formed.
• The alleles for different genes usually segregate
  independently of one another.

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Exceptions in Mendels work

• Some alleles are neither dominant nor recessive,
  and many traits are controlled by multiple
  alleles or multiple genes.

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Incomplete Dominance

• This complication is shown on four oclock
  plants.
• The F1 generation produced by a cross between
  red- flowered (RR) and white- flowered (WW) and
  have pink (RW) plants.

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Incomplete Dominance

• One allele is not completely dominant over
  another
• Heterozygous phenotype is somewhere in between
  the two homozygous phenotypes.

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Codominance

• Both alleles contribute to the phenotype.
• Heterozygous chicken have a color described as
  erminette speckled with black and white
  feathers.

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Multiple Allele

• Many genes have more than two alleles.
• More than two possible alleles exist in a
  population.
• A rabbits coat color is determined by a single
  gene that has at least four different alleles.

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Polygenic Trait

• Traits controlled by two or more genes.
• Often show a wide range of phenotypes.
• The wide range of skin color in humans comes
  partly because more than four different genes
  probably control this trait.

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Applying Mendels Principles

• In 1900 Thomas Hunt Morgan he was looking for a
  model of organism that was small, easy to keep in
  lab and produce large number of offspring.
• Fruit fly Drosophila melangaster

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Fruit fly Drosophila melangaster

• It produces plenty of offspring as many as 100.
• Morgan tested all of Mendels principles

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The basic principles of Mendelian genetics can be
used to study the inheritance of human traits and
to calculate the probability of certain traits
appearing in the next generation.
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Genetics and the Environment

• Characteristics are determined by the interaction
  between genes and the environment.
• Genes affect a sunflower plants height and the
  color of the flower
• Some characteristics are also influenced by
  climate, soil conditions and water availability.

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