Genetics and Heredity

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Genetics and Heredity

• Genetics is the study of heredity
• Heredity is how different genes are passed down
  from parents to children

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Genes

• Your GENES,
• not your JEANS.
• A gene is a segment of DNA that codes for a
  certain trait

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Genetics Terminology Genome, Chromosomes Genes

• ________ -Complete complement of an organisms
  DNA.
• Cellular DNA is organized in ___________.
• ______ have specific places on chromosomes.

From the Virtual Cell Biology Classroom on
ScienceProfOnline.com
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Gregor Mendel (lived in 1800s)

• Austrian monk who taught natural science
• Interested in how traits are passed on
• Crossbred snow pea plants to figure it out
• Is known as The father of Genetics
• Genetics- the study of heredity

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The work of Gregor Mendel

• Earlier Notions of Inheritance
• Blending
• Spermists
• Ovists
• Mendel was first to show both parents contribute
  equally

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Father of Genetics

• Mendel performed breeding experiments with garden
  peas
• Found mathematical patterns of inheritance
• His work was not appreciated until 1900, 16 years
  after his death

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Mendels work

• Why breed peas?
• They were available in many varieties,
  inexpensive, short life cycle, simple procedures,
  easy to grow.
• The use of plants also allowed strict control
  over the mating.
• He chose to study only characters that varied in
  an either-or rather than a more-or-less
  manner.

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Why peas?

• -not too many traits to keep track of
• -Pea traits-pea color, pea shape, plant height,
  pod shape, pod color, flower color, flower
  position

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• Mendel crossed purple flowers with white flowers.
  (Purebreds)
• - all of the resulting flowers were purple
• Then he let the F1s self-fertilize.
• Result in F2 generation
• -  75 of the flowers purple
• 25 of the flowers white
  Explain!

F1
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Interpreting Mendels Data
Parent Cross F1 generation F2 generation Actual Ratio Probability Ratio
Round x wrinkled 100 round 5,474 round 1,850 wrink. 2.961 31
Yellow x green pea 100 yellow 6,022 yell 2,001 green 3.011 31
Long x short stem 100 long stem 787 long 277 short 2.841 31
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Mendels Observations

• dominant vs recessive
• Before genes and meiosis were known, Mendel
  theorized inheritance factors
• are in the pollen and ova of peas as alternate
  forms for different traits.
• occur in pairs, (equal contribution from both
  parents)
• separate during gamete formation and pair up
  again at fertilization

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• Mendel's Laws
• 1. Law of Dominance
• 2. Law of Segregation
• 3. Law of Independent Assortment

Image Gregor Mendel, Mendel's Principles of
Heredity A Defense by Bateson, William.
From the Virtual Cell Biology Classroom on
ScienceProfOnline.com
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1. Mendels Law of _________
In a cross of parents that are pure for
contrasting traits, only one form of the trait
will appear in the next generation. 
Offspring that are hybrid for a trait will have
only the dominant trait in the phenotype.
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Mendels Law of Segregation

• Each hereditary characteristic is controlled by
  two factors (alleles) that separate and pass into
  reproductive cells (gametes).

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2. Mendels Law of ________
Table showing how the genes exchange according to
segregation or independent assortment during
meiosis and how this translates into Mendel's
laws.

• Alternative versions of genes (alleles) result in
  variations in inherited characteristics.
• For each character, an organism inherits 2
  alleles (one from each parent).
• The alleles for each character segregate
  (separate) during gamete production (_______).
• Alleles for a trait are recombined at
  fertilization, becoming genotype for the traits
  of the offspring.

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Mendels Law of Independent Assortment

• Pairs of inheritance factors (alleles) segregate
  independently of each other when sex cells
  (gametes) are formed.

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3. Mendels Law of _____ ______
Diagram of how the genes exchange according to
segregation or independent assortment during
meiosis and how this translates into Mendel's
laws.

• Alleles for different traits are distributed to
  sex cells ( offspring) independently of one
  another.
• Show me a video!
• RememberMendel came up with this stuff
  BEFORE we know about the existence of DNA, genes,
  chromosomes!

Image Independent assortment and segregation
diagram, Mariana Ruiz.
From the Virtual Cell Biology Classroom on
ScienceProfOnline.com
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Mendels Laws

• 1. Law of Dominance
• - In a cross of parents that are pure for
• contrasting traits, only one form of the
• trait will appear in the next generation.
•  
• - Offspring that are hybrid for a trait will
• have only the dominant trait in the phenotype.
• 2. Law of Segregations
• - During the formation of gametes (eggs or
  sperm), the two alleles (hereditary units)
  responsible for a trait separate from each
  other. 
• - Alleles for a trait are then "recombined" at
  fertilization, producing the genotype for the
  traits of the offspring.
• 3. Law of Independent Assortment
• - Alleles for different traits are distributed
  to sex cells ( offspring) independently of one
  another.

Image Gregor Mendel, Mendel's Principles of
Heredity A Defense by Bateson, William
From the Virtual Cell Biology Classroom on
ScienceProfOnline.com
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Mendelian Inheritance in Humansdominant
recessive

• Tongue Roller (T)
• Free Earlobes (F)
• Dimples (D)
• Widows Peak (P)

• Cant roll tongue (t)
• Attached lobes (f)
• No dimples (d)
• Straight hairline (w)

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Genetics and Probability

• Discuss
• Coin flipping
• Card picking
• Punnett Square probability vs actuality

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Some Vital Vocab.

• Genetics
• Gene vs Chromosome
• Alleles
• Dominant vs Recessive

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Some Vital Vocab.

• Genotype vs Phenotype
• Homozygous vs Heterozygous
• Diploid vs Haploid
• Mitosis vs Meiosis
• Zygote

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Problem Solving from Mendelian Genetics

• Consider inheritance patterns for
• Cystic Fibrosis
• Sickle Cell Anemia
• Huntingtons disease
• Hemophelia
• Colorblindness pedigree

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Exceptions to Complete Dominance

• Polygenic Traits
• Intermediate Expression (aka incomplete
  dominance)
• Multiple Alleles
• Several described at this link!