Mendel and His Peas

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Mendel and His Peas

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Objectives

• Explain the difference between cross and self
  pollination
• Explain the relationship between traits and
  heredity
• Describe the experiments of Gregor Mendel
• Explain the difference between dominant and
  recessive traits

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Heredity is

• The passing of traits from parent to offspring,
  and it is very complicated
• Different people have different traits, such as
  eye color, hair color, and ear lobes that do not
  attach directly to their head
• Where do people get these different traits?
• Many traits are inherited from parents and passed
  from parents to offspring through genes, which
  are a set of instructions for an inherited trait

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Gregor Mendel

• Born in 1882 on a farm in Austria
• Studied science at a monastery
• He discovered the principles of heredity in the
  monastery garden. Known as the Father of Genetics
• His research was mostly on plants
• He noticed that often a trait appeared in one
  generation (parents) and not present in the next
  generation (offspring)

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Anther
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Filament
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Pistil
Female Reproduction organ
A Wild Strawberry Flower
Male Reproduction organ
http//www.countrysideinfo.co.uk/flower.htm
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http//hordeum.oscs.montana.edu/home/documents/bb.
jpg
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Pollination

• Transfer of pollen from the anthers of the stamen
  to the stigma of the pistil.

Fertilization

• The union of one egg cell and one sperm cell.

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Pollination Video Clips

• http//www.fotosearch.com/DGV741/620009/ (Bee on
  flower)
• http//video.google.com/videoplay?docid5294323989
  667289565 (Importance of Honey Bees in
  pollination)
• The Pollination Song
• http//www.mbgnet.net/bioplants/pollination.html

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Self-Pollinating Peas

• Mendel wanted to find out more about patterns
  that traits take on from generation to generation
• To keep it simple, he focused on only one kind of
  organism peas
• Peas are self-pollinating, which means they have
  both male and female reproductive structures
• These are true breeding plants

Animation of self-pollination http//www.fs.fed.us
/wildflowers/pollinators/images/selfpollination.gi
f
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True Breeding

• All offspring have the same traits
• Examples
• True breeding plants with purple flowers will
  always produce purple flowers
• True breeding plants with long stems will always
  produce plants with long stems

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Cross-Pollination

• Peas can also cross-pollinate
• In cross-pollination pollen from one plant
  fertilizes the ovule of a flower on a different
  plant
• This can occur from insect travel or by wind

Cross-Pollination Animation http//www.fs.fed.us/w
ildflowers/pollinators/images/xpollination_ani.gif

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Cross-pollination
http//cache.eb.com/eb/image?id95388rendTypeId3
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Cross-Pollination by man
http//hordeum.oscs.montana.edu/home/documents/met
hods1.htm
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Mendel Studied Characteristics

• A characteristic is a feature that has different
  forms in a population. Examples hair color, eye
  color
• The different forms of a characteristic is called
  a trait . Examples red hair, blue eyes
• Mendel used peas to mix and match traits of
  different characteristics.

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Mendels First Experiments

• Mendel crossed true breeding pea plants to study
  7 characteristics
• The offspring from the cross of 2 true breeding
  plants are called the first generation plants
• In his experiment, one trait was always present
  and one trait seemed to disappear

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Dominant and Recessive Traits

• Dominant Trait the trait that was always
  present in the first generation
• Recessive Trait - all other traits seem to fade
  into the background, and are not shown in the
  first generation
• Dominant and Recessive traits appear in all
  organisms

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Mendels Second Experiment

• Mendel allowed first generation plants to
  self-pollinate
• The recessive trait reappeared in the second
  generation.
• He did the same with each of the other 6
  characteristics, in each case the recessive trait
  reappeared.

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Ratios in Mendels Experiments

• Mendel tried to figure out the ratio of dominant
  traits to recessive traits
• A ratio is a relationship between 2 numbers that
  is often expressed as a fraction (not always
  31 or 3 to 1)

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Mendel - Gone But Not Forgotten

• Each pea plant has 2 sets of instructions for
  each characteristic
• Each parent would donate 1 set of instructions
• Mendel published his results but it was 30 years
  after his death before he was recognized for his
  work.

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Traits and Inheritance

• Gene a set of instructions for a trait.
• Gene is made up of 2 or more parts called
  alleles. One comes from the biological mother
  and one from the biological father.
• Allele different forms of a gene.
• Dominant alleles are written with a capital
  letter.
• Recessive alleles are written with a lower case
  letter.

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Genes

• Chromosomes are in the nucleus of the cell.
• Chromosomes are made up of DNA.
• Genes are a section of DNA
• Alleles are part of a gene given to an organism
  from each parent.

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Human Chromosomes
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Female Chromosomes Matched
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Male Chromosomes Matched
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Alleles
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Phenotype

• Is an organisms appearance
• Written in words
• Example purple or white flowers
• Example brown eyes, blue eyes, hazel eyes. Green
  eyes

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Genotype

• Letters that represent the alleles for each
  trait.
• Dominant traits are written with capital letters
• Recessive traits are written with lower case
  letters.
• Homozygous an organism with either 2 Dominant or
  2 Recessive allele. True breed.
• Example TT (Tall plant) tt (short plant)
• Heterozygous an organism with one Dominant
  allele and one Recessive allele.
• Example Tt (Tall plants)

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Punnett Square

• Used to calculate the possible outcomes of a
  genetic cross.
• The alleles from both parents are placed