Genetics

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Genetics

• The study of heredity

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Gregor Mendel

• Mendel was an Austrian monk.
• Mendel formulated two fundamental laws of
  heredity in the early 1860's.
• He had studied science and mathematics (including
  statistics) at the University of Vienna.
• Mendels knowledge of statistics later proved
  valuable in his research on Heredity the
  transmission of characteristics from Parent to
  Offspring.
• Mendel's work was unrecognized until 1900.

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Genetics Vocabulary

• Monohybrid cross - cross involving a single pair
  of genes, one trait
• P parents
• F1 kids
• F2 grandkids

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• Law of Segregation Each organism contains two
  factors for each trait factors segregate in the
  formation of gametes. When two gametes combine
  during fertilization, the offspring have two
  factors controlling a specific trait.
• Law of Independent Assortment states that
  factors for different characteristics are
  distributed to gametes independently.

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Genetics Vocabulary

• Gene - the unit of heredity a section of DNA
  sequence encoding a single protein
• Alleles - two genes that occupy the same position
  on homologous chromosomes and cover the same
  trait
• Locus - a fixed location on a strand of DNA where
  a gene or one of its alleles is located
• Trait observed
• expression of the gene
• (Physical manifestation
• of information)

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F1 Crosses
Seed Shape
Flower Position
Seed Coat Color
Seed Color
Pod Color
Plant Height
Pod Shape
Round
Yellow
Gray
Smooth
Green
Axial
Tall
Wrinkled
Green
White
Constricted
Yellow
Terminal
Short
Round
Yellow
Gray
Smooth
Green
Axial
Tall
In the first generation of each experiment, how
do the characteristics of the offspring compare
to the parents characteristics?
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Genetics Vocabulary

• Dominant - the trait that appears in the
  heterozygous condition.
• Dominant allele ? capital letter Height
  ex T tall
• Recessive - the trait that is masked in the
  heterozygous condition.
• Recessive allele ? lowercase letter
• Height ex t short

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Mendels 3rd Law Principle of Dominance

• 2. Some alleles are

DOMINANT
recessive
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Genetics Vocabulary

• Homozygous - having identical genes (one from
  each parent) for a particular characteristic.
• Heterozygous - having two different genes for a
  particular characteristic.

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Genotype Phenotype
Genotype Phenotype
Genetic makeup Cant see Height ex TT, Tt, or tt (letter code) Physical characteristic/appearance Can see Depends on genotype Height ex tall or short
Question Can two organisms have the same
phenotype but have different genotypes? Explain.
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Traits exist because of 2 alleles

• Every trait has 2 _______ that determines its
  phenotype.
• AA or Aa or aa
• AA Homozygous Dominant
• Aa Heterozygous
• aa ___________ __________
• It is because of this, that the recessive trait
  can disappear in the F1 generation.

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Genetics Vocabulary

• Punnett squares - used to aid in predicting the
  probability that certain traits will be inherited
  by offspring
• Probability - is the likelihood that a specific
  event will occur or is the likely outcome a given
  event will occur from random chance

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Monohybrid Crosses

• 1. Determine the dominant and recessive trait

Will be stated in the problem ie. Black is
dominant to white in bunnies
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• 2. Assign letters for the trait

Dominant trait gets the capital letter Recessive
traits gets the lower case letter B black b
white
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• 3. Determine genotype for parents

White male bb Heterozygous black female Bb
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• 4. Put parents on the square

Bb x bb B b b b


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Punnett square holds offspring genotypes
B b b b Genotype
letter code

• 5. Determine genotype of offspring

Bb bb
Bb bb
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• 6. Determine genotype ratio

Count offspring in the Punnett square genotype
ratio 2Bb2bb
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Phenotype what they look like Count offspring
in the Punnett square phenotype ratio 2
black2 white If ratio doesnt add up to total
number of boxes in the punnett square youve made
a mistake

• 7. Determine phenotype ratio

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Practice Problems

• A pure-breed white flower crosses with a
  pure-breed purple flower. Purple is dominant to
  white.
• Show the punnett square
• What is the genotype of the F1 generation
• What is the phenotype of the F1 generation

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Genotype Pp Phenotype Purple
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More practice

• A homozygous black rat is crossed with a
  heterozygous black rat.
• B black b brown
• Show the punnett square
• What are the genotypes of F1?
• What are the genotype ratio of F1?

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Genotypes BB and Bb Genotype Ratio 2BB2Bb
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More practice

• If you had a black rat how could you tell its
  genotype was homozygous or heterozygous?

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Use a test cross cross with a pure breed
(homozygous) recessive and look at the F1
generation
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Possible Answer Formats

• - chance out of total possible
• 1 out of 4 25
• Fraction
• 1 out of 4 1/4
• Ratio ratio adds up to total possible
• 1 out of 4 13