Fundamentals of Genetics

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Fundamentals of Genetics

• Chapter 9

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Heredity

• The passing of traits from parents to offspring
• Traits are characteristics like hair color, pea
  plant height, the ability to roll your tongue,
  blood type
• Traits are controlled by genes, which are found
  on chromosomes
• GeneticsThe study of heredity

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Gregor Mendel

• The Father of Genetics
• Austrian monk in charge of the gardens at the
  monastery
• He was interested in pea plants

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Gregor Mendel cont.

• Specifically, why did the plants have different
  traits?
• For example--why did some have green seeds and
  some have yellow seeds
• He experimented with the plants. His accidental
  choice of pea plants served as the foundation for
  future genetic studies

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Pea Plant Traits
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Why was Mendel Successful with the Peas?

• Easy to control their pollination
• He used pure-breeding, contrasting varieties
• Pure/True Breedingif allowed to self fertilize,
  will only produce offspring exactly like them
• Studied one characteristic at time for many
  generations
• Used statistics to analyze his results
• Obtained large number of offspring

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Gregor Mendel cont.

• So what exactly did Mendel do? Very basically,
  he mated different plants together, counted the
  types of offspring produced, and then looked for
  patterns.

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Mendels Experiment

• First he crossed (mated) a true breeding round
  seed with a true breeding wrinkle seed plant
• This was his parental (P) generation)

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Mendels Experiment cont

• All the offspring in his first generation (F1)
  were
• ROUND
• He was surprised because the wrinkled trait
  seemed to have disappeared in the F1 offspring

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Mendels Experiment cont

• Next he allowed an F1 offspring to fertilize
  itself
• Round X Round
• The resulting
• offspring were
• ¾ round
• ¼ wrinkled
• This is the F2 gen.

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Mendels Experiment cont

• He was surprised again, the wrinkled trait hadnt
  disappear, it must have been hidden
• Hidden in the F1 plant
• It then reappeared in some of the F2 plants
• Mendel repeated the experiment for other traits
• Seed color, flower position, plant height

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Mendels Conclusions

• Each organism has two genes controlling each
  trait. One gene comes from the mother, the other
  comes from the father

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Terminology

• Dominantone gene in a pair that prevents the
  other gene from being expressed/shown
• A dominant gene is a printed, capital letter
• Recessivegene that is hidden by the dominant
  gene
• A recessive gene is a cursive, lower case letter

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Terminology cont.

• Homozygoustwo genes in the pair are identical
  (aka purebred)
• ExamplesTT or tt
• Heterozygoustwo genes in a pair are different
  (aka hybrid)
• ExampleTt

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Terminology cont.

• GenotypeThe genetic makeup of an organism
• Examples TT, Tt or tt
• PhenotypeThe physical appearance of an organism
• Tall, short, purple

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Terminology cont.

• Alleledifferent choices of phenotype for a
  gene
• Your trait could be hair color and your alleles
  could be beige, blonde, brown, black and red

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Law of Segregation

• Remember that genes occur in pairs
• Each gamete receives only one allele of each pair
  (in other words, the alleles segregate)
• So if you have Aa 50 of the eggs will receive
  the A and the other 50 will receive the a

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Law of Segregation cont.

• If you have an organism with H H
• 50 will get H
• 50 will get H
• Or 100 of the eggs/sperm will get an H

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Law of Independent Assortment

• Another law belonging to Mendel
• Will be addressed at another time

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So Lets Go Back to Mendels Experiment
RR
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hybrids
Rr
Rr
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RR
Rr
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