Mendel

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Mendel Genetics

• Chapter 11-1 and 11-2

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Gregor Mendel

• Gregor Mendel- (1843) an Austrian monk who
  developed the principal of dominance by
  experimenting with pea plants in a monastery
  garden

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Fertilization

• Fertilization- when male and female reproductive
  cells (sperm and egg) join
• Because plants have both male and female
  reproductive cells, they are able to fertilize
  themselves (self pollination)
• True-breeding- if allowed to self-pollinate, they
  would produce offspring identical to themselves

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Mendels Experiments

• Mendel wanted to produce offspring from different
  plant parents
• To do this, he had to keep the plants from
  self-pollinating
• He did this by cutting away the male parts of the
  plant, and then dusting the plant with pollen
  from another plant (cross-pollination)
• Figure 11-3

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Cross Pollination
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Genes Dominance

• Trait- a specific characteristic that varies from
  one individual to another (examples seed color,
  plant height)
• Mendel studied seven traits in pea plants

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Genes Dominance

• P1 Generation- parental generation/ original
  plants
• F1 Generation- first filial first generation
  of offspring offspring of P1
• F2 Generation- second filial second
  generation offspring of F1

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Genes Dominance

• Because of cross-pollination, the F1 generation
  Mendel created were hybrids
• Hybrids- offspring of parents with different
  traits

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Genes Dominance

• After cross-pollinating the P1 generation, Mendel
  observed the offspring (F1 Generation)
• All of the offspring had the character of only
  one of the parents!

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Mendels Conclusions

• Biological inheritance is determined by factors
  passed from one generation to the next
• The principal of dominance- some alleles are
  dominant and some are recessive

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First Conclusion

• Biological inheritance is determined by factors
  passed from one generation to the next
• Scientists call these chemical factors genes
• Genes exist in two contrasting forms (example
  gene for plant height can be short or tall)
• Different forms of genes are called alleles

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Second Conclusion

• The principal of dominance- some alleles are
  dominant and some are recessive
• An organism with a dominant allele will always
  exhibit that form of the trait
• Example in the gene for plant height, tall is
  the dominant allele. Any plants having at least
  one tall allele will grow tall.

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Segregation

• Mendel wanted to know what happened to recessive
  alleles after the first cross
• He crossed the F1 generation with each other to
  produce an F2 generation by self-pollination
• Figure 11-4

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Results of the F1 Cross

• After crossing the F1 generation, Mendel observed
  that recessive traits appeared in ¼ of the
  offspring

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Explaining the F1 Cross

• How do recessive alleles appear in the F2
  generation and not the F1 generation?
• Segregation- separation of alleles
• Dominant and recessive alleles are segregated in
  the formation of sex cells
• Gametes- haploid sex cells carries only one copy
  of each gene (example one gamete gets the short
  allele, the other gets the tall allele)

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Punnett Squares

• Used to predict and compare the genetic variation
  that will result from a cross

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Punnett Square Vocabulary

• Homozygous- two identical alleles for a
  particular trait (example TT or tt)
• Heterozygous- two different alleles for a
  particular trait (example Tt)

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Punnett Square Vocabulary

• Phenotype- physical characteristics
• Genotype- genetic makeup
• Organisms can have the same phenotype, but
  different genotypes!